A systematic literature review of 10 years of research on sex/gender and pain perception - part 2: do biopsychosocial factors alter pain sensitivity differently in women and men?

The role of gonadal hormones in regulating opioid antinociception

Opioids are the most prescribed drugs for the alleviation of pain. Both clinical and preclinical studies have reported strong evidence for sex-related divergence regarding opioid analgesia. There is an increasing amount of evidence indicating that gonadal hormones regulate the analgesic efficacy of opioids. This review presents an overview of the importance of gonadal steroids in modulating opioid analgesic responsiveness and focuses on elaborating what is currently known regarding the underlyingmechanism. We sought to identify the link between gonadal hormones and the effect of oipiod antinociception.

Associations between pain intensity, pain sensitivity, demographics, psychological factors, disability, physical activity, pain phenotype and COVID-19 history in low back pain: An observational study

BACKGROUND AND PURPOSE

Knowledge of the factors affecting pain intensity and pain sensitivity can inform treatment targets and strategies aimed at personalizing the intervention, conceivably increasing its positive impact on patients. Therefore, this study aimed to investigate the association between demographic factors (sex and age), body mass index (BMI), psychological factors (anxiety and depression, kinesiophobia and catastrophizing), self-reported physical activity, pain phenotype (symptoms of central sensitization, and nociceptive or neuropathic pain), history of COVID-19 and pain intensity and sensitivity in patients with chronic non-specific low back pain (LBP).

METHODS

This was a cross-sectional secondary analysis with 83 participants with chronic non-specific LBP recruited from the community between August 2021 and April 2022. BMI, pain intensity (Visual Analog Scale), pain sensitivity at the lower back and at a distant point [pressure pain threshold], catastrophizing (Pain Catastrophizing Scale), kinesiophobia (Tampa Scale for Kinesiophobia), anxiety and depression (Hospital Anxiety and Depression Scale), pain phenotype (Central Sensitization Inventory and PainDetect Questionnaire), physical activity (International Physical Activity Questionnaire), and disability (Roland Morris Disability Questionnaire) were assessed. Multiple linear regression analyses with pain intensity and sensitivity as the dependent variables were used.

RESULTS

The model for pain intensity explained 34% of its variance (Adjusted R2 = -0.343, p < 0.001), with depression and anxiety (p = 0.008) and disability (p = 0.035) reaching statistical significance. The model for pain sensitivity at the lower back, also explained 34% of its variance (Adjusted R2 = 0.344, p < 0.001) at the lower back with sex, BMI, and kinesiophobia reaching statistical significance (p < 0.05) and 15% of the variance at a distant body site (Adjusted R2 = 0.148, p = 0.018) with sex and BMI reaching statistical significance (p < 0.05).

DISCUSSION

This study found that different factors are associated with pain intensity and pain sensitivity in individuals with LBP. Increased pain intensity was associated with higher levels of anxiety and depression and disability and increased pain sensitivity was associated with being a female, higher kinesiophobia, and lower BMI.

Weak Relationships Between Psychological Factors and Experimental Pain Outcomes in Pain-Free Individuals: An Aggregate Analysis of 8 Studies

Although psychological factors such as anxiety, depression, and pain catastrophizing are known to influence pain outcomes in chronic pain populations, there are mixed results regarding whether they influence experimental pain outcomes in pain-free individuals. The objectives of this study were to determine the associations between psychological factors and experimental pain outcomes in pain-free adolescents and adults. Relationships between anxiety, depression, and pain catastrophizing and experimental pain outcomes across 8 different studies (total N = 595) were examined in different populations of pain-free adult and adolescent participants. Analyses were conducted with and without controlling for sex, age, and race. Studies were analyzed separately and as part of an aggregate analysis. Individual study analyses resulted in 136 regression models. Of these, only 8 models revealed a significant association between psychological factors and pain outcomes. The significant results were small and likely due to Type 1 error. Controlling for demographic factors had minimal effect on the results. The aggregate analyses revealed weak relationships between anxiety and pressure pain threshold (Fisher's z = -.10 [-.19, -.01]), anxiety and cold pain intensity ratings (Fisher's z = .18 [.04, .32]), and pain catastrophizing and pressure pain threshold (Fisher's z = -.14 [-.26, -.02]). Sample size calculations based on the aggregate analyses indicated that several hundred participants would be required to detect true relationships between these psychological factors and pain measures. The overall negative findings suggest that in pain-free individuals, anxiety, depression, and pain catastrophizing are not meaningfully related to experimental pain outcomes. PERSPECTIVE: Psychological variables have been shown to predict pain outcomes in chronic pain populations but these relationships may not generalize to pain-free populations. An analysis of 595 pain-free individuals across 8 studies in our lab revealed that anxiety, depression, and pain catastrophizing were not meaningfully related to experimental pain outcomes.

Healthy women show more experimentally induced central sensitization compared with men

ABSTRACT

Women more often experience chronic pain conditions than men. Central sensitization (CS) is one key mechanism in chronic pain that can differ between the sexes. It is unknown whether CS processes are already more pronounced in healthy women than in men. In 66 subjects (33 women), a thermal CS induction protocol was applied to the dorsum of one foot and a sham protocol to the other. Spatial extent [cm 2 ] of secondary mechanical hyperalgesia (SMH) and dynamic mechanical allodynia were assessed as subjective CS proxy measures, relying on verbal feedback. Changes in nociceptive withdrawal reflex magnitude (NWR-M) and response rate (NWR-RR) recorded through surface electromyography at the biceps and rectus femoris muscles were used as objective CS proxies. The effect of the CS induction protocol on SMH was higher in women than in men (effect size 2.11 vs 1.68). Nociceptive withdrawal reflex magnitude results were statistically meaningful for women (effect size 0.31-0.36) but not for men (effect size 0.12-0.29). Differences between men and women were not meaningful. Nociceptive withdrawal reflex response rate at the rectus femoris increased in women after CS induction and was statistically different from NWR-RR in men (median differences of 13.7 and 8.4% for 120 and 140% reflex threshold current). The objective CS proxy differences indicate that dorsal horn CS processes are more pronounced in healthy women. The even larger sex differences in subjective CS proxies potentially reflect greater supraspinal influence in women. This study shows that sex differences are present in experimentally induced CS in healthy subjects, which might contribute to women's vulnerability for chronic pain.

Principles of musculoskeletal sport injuries for epidemiologists: a review

BACKGROUND

Musculoskeletal injuries are a common occurrence in sport. The goal of sport injury epidemiology is to study these injuries at a population level to inform their prevention and treatment.

MAIN BODY

This review provides an overview of musculoskeletal sport injuries and the musculoskeletal system from a biological and epidemiologic perspective, including injury mechanism, categorizations and types of sport injuries, healing, and subsequent injuries. It is meant to provide a concise introductory substantive background of musculoskeletal sport injuries for epidemiologists who may not have formal training in the underlying anatomy and pathophysiology.

CONCLUSION

An understanding of sport injuries is important for researchers in sport injury epidemiology when determining how to best define and assess their research questions and measures.

How to make calibration less painful-A proposition for an automatic, reliable and time-efficient procedure

In behavioral and neurophysiological pain studies, multiple types of calibration methods are used to quantify the individual pain sensation stimuli. Often, studies lack a detailed calibration procedure description, data linearity, and quality quantification and omit required control for sex pain differences. This hampers study repetition and interexperimental comparisons. Moreover, typical calibration procedures require a high number of stimulations, which may cause discomfort and stimuli habituation among participants. To overcome those shortcomings, we present an automatic calibration procedure with a novel stimuli estimation method for intraepidermal stimulation. We provide an in-depth data analysis of the collected self-reports from 70 healthy volunteers (37 males) and propose a method based on a dynamic truncated linear regression model (tLRM). We compare its estimates for the sensation (t) and pain (T) thresholds and mid-pain stimulation (MP), with those calculated using traditional estimation methods and standard linear regression models. Compared to the other methods, tLRM exhibits higher R2 and requires 36% fewer stimuli applications and has significantly higher t intensity and lower T and MP intensities. Regarding sex differences, t and T were found to be lower for females compared to males, regardless of the estimation method. The proposed tLRM method quantifies the calibration procedure quality, minimizes its duration and invasiveness, and provides validation of linearity between stimuli intensity and subjective scores, making it an enabling technique for further studies. Moreover, our results highlight the importance of control for sex in pain studies.

Assessing Risk Factors and Comorbidities in the Treatment of Chronic Pain: A Narrative Review

PURPOSE OF REVIEW

Chronic pain affects a significant portion of the population globally, making it a leading cause of disability. Understanding the multifaceted nature of chronic pain, its various types, and the intricate relationship it shares with risk factors, comorbidities, and mental health issues like depression and anxiety is critical for comprehensive patient care. Factors such as socioeconomic status (SES), age, gender, and obesity collectively add layers of complexity to chronic pain experiences and pose management challenges.

RECENT FINDINGS

Low SES presents barriers to effective pain care, while gender differences and the prevalence of chronic pain in aging adults emphasize the need for tailored approaches. The association between chronic pain and physical comorbidities like cardiovascular disease, chronic obstructive pulmonary disease (COPD), and diabetes mellitus reveals shared risk factors and further highlights the importance of integrated treatment strategies. Chronic pain and mental health are intricately linked through biochemical mechanisms, profoundly affecting overall quality of life. This review explores pharmacologic treatment for chronic pain, particularly opioid analgesia, with attention to the risk of substance misuse and the ongoing opioid epidemic. We discuss the potential role of medical cannabis as an alternative treatment with a nuanced perspective on its impact on opioid use. Addressing the totality and complexity of pain states is crucial to individualizing chronic pain management. With different types of pain having different underlying mechanisms, considerations should be made when approaching their treatment. Moreover, the synergistic relationship that pain states can have with other comorbidities further complicates chronic pain conditions.

Identifying clusters of objective functional impairment in patients with degenerative lumbar spinal disease using unsupervised learning

OBJECTIVES

The five-repetition sit-to-stand (5R-STS) test was designed to capture objective functional impairment (OFI), and thus provides an adjunctive dimension in patient assessment. It is conceivable that there are different subsets of patients with OFI and degenerative lumbar disease. We aim to identify clusters of objectively functionally impaired individuals based on 5R-STS and unsupervised machine learning (ML).

METHODS

Data from two prospective cohort studies on patients with surgery for degenerative lumbar disease and 5R-STS times of ≥ 10.5 s-indicating presence of OFI. K-means clustering-an unsupervised ML algorithm-was applied to identify clusters of OFI. Cluster hallmarks were then identified using descriptive and inferential statistical analyses.

RESULTS

We included 173 patients (mean age [standard deviation]: 46.7 [12.7] years, 45% male) and identified three types of OFI. OFI Type 1 (57 pts., 32.9%), Type 2 (81 pts., 46.8%), and Type 3 (35 pts., 20.2%) exhibited mean 5R-STS test times of 14.0 (3.2), 14.5 (3.3), and 27.1 (4.4) seconds, respectively. The grades of OFI according to the validated baseline severity stratification of the 5R-STS increased significantly with each OFI type, as did extreme anxiety and depression symptoms, issues with mobility and daily activities. Types 1 and 2 are characterized by mild to moderate OFI-with female gender, lower body mass index, and less smokers as Type I hallmarks.

CONCLUSIONS

Unsupervised learning techniques identified three distinct clusters of patients with OFI that may represent a more holistic clinical classification of patients with OFI than test-time stratifications alone, by accounting for individual patient characteristics.

Interindividual variability in cold-pressor pain sensitivity is not explained by peripheral vascular responding and generalizes to a C-nociceptor-specific pain phenotype

ABSTRACT

Pain sensitivity of healthy subjects in the cold-pressor (CP) test was proposed to be dichotomously distributed and to represent a pain sensitivity trait. Still, it has not been systematically explored which factors influence this pain sensitivity readout. The aim of this study was to distinguish potential contributions of local tissue-related factors such as perfusion and thermoregulation or gain settings in nociceptive systems. Cold-pressor-sensitive and CP-insensitive students screened from a medical student laboratory course were recruited for a CP retest with additional cardiovascular and bilateral local vascular monitoring. In addition, comprehensive quantitative sensory testing according to Deutscher Forschungsverbund Neuropathischer Schmerz standards and a sustained pinch test were performed. Cold pressor was reproducible across sessions (Cohen kappa 0.61 ± 0.14, P < 0.005). At 30 seconds in ice water, CP-sensitive subjects exhibited not only more pain (78.6 ± 26.3 vs 29.5 ± 17.5, P < 0.0001) but also significantly stronger increases in mean arterial blood pressure (12.6 ± 9.3 vs 5.6 ± 8.1 mm Hg, P < 0.05) and heart rate (15.0 ± 8.2 vs 7.1 ± 6.2 bpm, P < 0.005), and lower baroreflex sensitivity, but not local or vasoconstrictor reflex-mediated microcirculatory responses. Cold-pressor-sensitive subjects exhibited significantly lower pain thresholds also for cold, heat, and blunt pressure, and enhanced pain summation, but no significant differences in Aδ-nociceptor-mediated punctate mechanical pain. In conclusion, differences in nociceptive signal processing drove systemic cardiovascular responses. Baroreceptor activation suppressed pain and cardiovascular responses more efficiently in CP-insensitive subjects. Cold-pressor sensitivity generalized to a pain trait of C-fiber-mediated nociceptive channels, which was independent of local thermal and vascular changes in the ice-water-exposed hand. Thus, the C-fiber pain trait reflects gain setting of the nociceptive system.

Pharmacological Prescribing and Satisfaction with Pain Treatment Among Non-Hispanic Black Men with Chronic Pain

Introduction

Pharmacological strategies are often central to chronic pain management; however, pain treatment among non-Hispanic Black men may differ because of their disease profiles and healthcare interactions. However, less is known about pain medication prescribing and patients' satisfaction with pain treatment and management among non-Hispanic Black men with self-reported chronic pain.

Purpose

This study assessed factors associated with non-Hispanic Black men being prescribed/recommended narcotics/opioids for chronic pain and their satisfaction with pain treatment/management.

Methods

Data were analyzed from 286 non-Hispanic Black men with chronic pain who completed an internet-delivered questionnaire. Participants were recruited nationwide using a Qualtrics web-based panel. Logistic regression was used to identify factors associated with being prescribed/recommended narcotics/opioids for pain management treatment. Then, ordinary least squares regression was used to identify factors associated with their satisfaction level with the pain treatment/management received.

Results

On average, participants were 56.2 years old and 48.3% were prescribed/recommended narcotics/opioids for chronic pain. Men with more chronic conditions (Odds Ratio [OR] = 0.57, P = 0.043) and depression/anxiety disorders (OR = 0.53, P = 0.029) were less likely to be prescribed/recommended narcotics/opioids. Men who were more educated (OR = 2.09, P = 0.044), reported more frequent chronic pain (OR = 1.28, P = 0.007), and were allowed to participate more in decisions about their pain treatment/management (OR = 1.11, P = 0.029) were more likely to be prescribed/recommended narcotics/opioids. On average, men with more frequent chronic pain (B = -0.25, P = 0.015) and pain problems (B = -0.16, P = 0.009) were less satisfied with their pain treatment/management. Men who were allowed to participate more in decisions about their pain treatment/management reported higher satisfaction with their pain treatment/management (B = 0.55, P < 0.001).

Conclusion

Playing an active role in pain management can improve non-Hispanic Black men's satisfaction with pain treatment/management. This study illustrates the importance of patient-centered approaches and inclusive patient-provider interactions to improve chronic pain management.

Pain Education in the Wellness, Training Performance, and Pain Intensity of Youth Athletes: An Experimental Study

BACKGROUND

Although pain management programs reduce pain and improve wellness perception in the general population, few studies have explored these effects in athletes. This study evaluated the effects of an educational program about pain neuroscience on wellness, training performance, and pain in youth athletes. Differences according to sex were also explored.

METHODS

For 12 weeks, 52 athletes were randomly assigned to an intervention group (IG: educational program about healthy sports habits and pain neuroscience) or a control group (CG: education on healthy sports habits only). Before the start of the study and weekly until its end, wellness, training performance, and pain intensity were monitored via a questionnaire.

RESULTS

After the intervention, IG decreased stress (p = 0.028) compared to the baseline, and a higher number of training sessions were performed without health problems (76.6%) compared to the number in the CG (63.0%) (χ2 = 8.31, p = 0.004). Regarding pain, the IG perceived lower pain than the CG did (p = 0.028). Females in the IG had lower pain than those in the CG did (p < 0.05), without differences in other variables or in males (p > 0.05).

CONCLUSIONS

An educational program that includes pain neuroscience may help youth athletes improve their wellness status, pain intensity perception, and training session performance.

Sex moderates the association between quantitative sensory testing and acute and chronic pain after total knee/hip arthroplasty

OBJECTIVES

Acute postsurgical pain (APSP) may persist over time and become chronic. Research on predictors for APSP and chronic postsurgical pain (CPSP) has produced inconsistent results. This observational study aimed to analyze psychological and psychophysical variables associated with APSP and CPSP after total knee or hip arthroplasty, and to explore the role of sex.

METHODS

Assessments were conducted before surgery, 48 h, and 3 months postsurgery, including questionnaires (sociodemographic, pain related, and psychological) and quantitative sensory testing (QST). Hierarchical linear regression models analyzed potential predictors of APSP and CPSP, and moderation analyses evaluated the role of sex.

RESULTS

The study included 63 participants undergoing total knee (34, 54%) or hip (29, 46%) arthroplasty. Thirty-one (49.2%) were female and 32 (50.8%) were male. APSP (48 h) was associated with impaired conditioned pain modulation (CPM) (β = 0.301, p = 0.019). CPSP (3 months) was associated with being female (β = 0.282, p = 0.029), longer presurgical pain duration (β = 0.353, p = 0.006), knee arthroplasty (β = -0.312, p = 0.015), higher APSP intensity (β = 373, p = 0.004), and impaired CPM (β = 0.126, p = 0.004). In multivariate analysis, these clinical variables were significant predictors of CPSP, unlike sex, and CPM (adj. R 2 = 0.349). Moderation analyses showed that wind-up ratio (WUR) was a significant predictor of APSP in men (WUR × sex: b = -1.373, p = 0.046) and CPM was a significant predictor of CPSP in women (CPM × sex: b = 1.625, p = 0.016).

CONCLUSIONS

Specific QST parameters could identify patients at risk for high-intensity APSP and CPSP, with sex as a moderator. This has important clinical implications for patient care, paving the way for developing tailored preventive pain management strategies.

Sex differences in COVID-19 symptom severity and trajectories among ambulatory adults

Background

The ongoing COVID-19 pandemic has led to hundreds of millions of infections worldwide. Although differences in COVID-19 hospitalization rates between males and females have been described, many infections in the general population have been mild, and the severity of symptoms during the course of COVID-19 in non-hospitalized males and females is not well understood.

Methods

We conducted a case-ascertained study to examine household transmission of SARS-CoV-2 infections in Nashville, Tennessee, between April 2020 and April 2021. Among enrolled ambulatory adult participants with laboratory-confirmed SARS-CoV-2 infections, we assessed the presence and severity of symptoms (total, systemic, and respiratory) daily using a symptoms severity questionnaire, from illness onset and throughout the 2-week follow-up period. We compared the mean daily symptom severity scores (0-3: none, mild, moderate, and severe) and change in symptoms between males and females using a multivariable linear mixed effects regression model.

Results

The analysis included 223 enrolled adults with SARS-CoV-2 infection (58% females, mostly white, non-Hispanic) from 146 households with 2917 total daily symptom reports. The overall mean severity of total symptoms reported over the illness period was 1.04 and 0.90 for females and males, respectively. Mean systemic and respiratory scores were higher for females than for males (p < 0.001). In multivariable analyses, females reported more severe total and systemic symptoms during the illness period compared with males. However, no significant differences in reported respiratory symptoms were observed.

Conclusions

Our findings indicate that among ambulatory adults with SARS-CoV-2 infections, females reported slightly higher symptom severity during their illness compared with males.

Sex Differences in Pain and Quantitative Sensory Testing in Patients With Rheumatoid Arthritis

OBJECTIVE

Women with rheumatoid arthritis (RA) have higher pain and worse functional outcomes compared to men, even when treated with similar medications. The objective of this study was to identify sex differences in pain intensity, pain interference, and quantitative sensory tests (QST), which are independent of inflammation, in patients with RA.

METHODS

This study is a post hoc analysis of participants in the Central Pain in Rheumatoid Arthritis cohort. Pain intensity was assessed using a 0-10 numeric rating scale. Pain interference was measured using a Patient-Reported Outcomes Measurement Information System computerized adaptive test. QST included pressure pain detection thresholds, temporal summation, and conditioned pain modulation. Women and men were compared using multiple linear regression, adjusted for age, education, race, research site, depression, obesity, RA disease duration, swollen joint count, and C-reactive protein.

RESULTS

Mean ± SD pain intensity was 5.32 ± 2.29 among women with RA, compared to 4.60 ± 2.23 among men with RA (adjusted difference 0.83 [95% confidence interval (95% CI) 0.14, 1.53]). Women with RA had lower pressure pain detection thresholds at the trapezius (adjusted difference -1.22 [95% CI -1.73, -0.72]), wrist (adjusted difference -0.57 [95% CI -1.07, -0.06]), and knee (adjusted difference -1.10 [95% CI -2.00, -0.21]). No statistically significant differences in pain interference, temporal summation, and conditioned pain modulation were observed.

CONCLUSION

Women reported higher pain intensity and lower pressure pain detection thresholds (higher pain sensitivity) than men. However, pain interference, temporal summation, and conditioned pain modulation did not differ between men and women.

Epidemiology of non-oncological high-impact chronic pain in Ecuadorian adults in 2022

Background: There are limited data on non-oncological high-impact chronic pain (HICP) in Ecuador; we report the epidemiological characteristics of HICP. Materials & methods: In this cross-sectional study, we included a random sample of adult individuals who had cell phones. Results & conclusion: The weighted prevalence of HICP was 9.0%: 12.3% for women and 5.6% for men (p = 0.001). HICP was more frequently localized in the lower back and affected the economically active population. Nonsteroidal anti-inflammatory drugs were more commonly used; however, 61% of patients indicated that the effectiveness of their management was low. Overall, HICP had a negative impact on daily life activities. The effectiveness of the current treatment was low and should include an integrated approach.

Factors Associated With Residual Disease in Axial Spondyloarthritis: Results From a Clinical Practice Registry

OBJECTIVE

To explore residual disease, defined as substantial symptoms and disease burden despite a remission or low disease activity (LDA) state, in patients with axial spondyloarthritis (axSpA), and to determine which factors are associated with residual disease.

METHODS

For this cross-sectional observational study, 1 timepoint per patient was used from SpA-Net, a web-based monitoring registry for SpA. Patients with an Ankylosing Spondylitis Disease Activity Score (ASDAS) < 2.1 (LDA) were included. Indicators of residual disease (outcomes) included fatigue (primary outcome), pain, physical functioning, health-related quality of life (HRQOL), and peripheral symptoms. Sex was the primary explanatory factor for residual disease. Other explanatory factors included demographics and disease-related factors. Associations between these factors and presence and extent of residual disease were explored using logistic and linear regression.

RESULTS

In total, 267 patients in an LDA state were included. Mean age was 50.6 (SD 14.3) years and 100 (37.5%) were female. Residual disease occurred frequently (n = 114 [42.7%] had fatigue scores > 4/10; n = 34 [17.8%] had pain scores > 4/10), including in those in remission (ASDAS < 1.3). Physical HRQOL was reduced in 27% and moderate/poor in 33%. Multivariable regression analyses showed that reported fatigue was more severe and prevalent in female patients (fatigue severity [0-10]: Bfemale = 0.78, 95% CI 0.18-1.38; fatigue > 4/10: ORfemale = 3.29, 95% CI 1.74-6.20). Other indicators of residual disease (ie, pain, peripheral symptoms, physical HRQOL) were also more severe and/or more prevalent in females.

CONCLUSION

Residual disease is frequent in patients with axSpA who are in an LDA state, including remission, and it is particularly prevalent in female patients. Future studies should address how to manage or prevent residual disease in axSpA.

Communication of pain intensity and unpleasantness through magnitude ratings: Influence of scale type, but not gender of the participant

BACKGROUND

A critical aspect for most human pain research is the ability of participants to communicate their first-person, experiential perspective to a third-person observer. This communication is frequently accomplished via pain ratings. The scale type can influence the communication of pain experiences and can contribute to gender differences in pain. This study examined the role of gender on pain ratings using noxious and innocuous stimuli across two types of rating scales.

METHODS

Healthy participants (n = 46) underwent noxious heat, auditory and visual stimulation paradigms. Pain intensity and unpleasantness ratings were collected using the visual analogue scale (VAS) and numerical rating scale (NRS). To determine if one rating scale allows a better report of small differences between different stimulus intensities, the sensitivity to small differences was calculated.

RESULTS

Significant effects for rating scale were found for all stimulus modalities (noxious heat, auditory and visual, p < 0.001) with higher intensity and unpleasantness ratings for the NRS compared to the VAS. Overall, no effects of gender or interactions with gender were found. No differences in rating scale and gender were detected for sensitivity to small differences between stimuli.

CONCLUSIONS

These findings confirm differences in rating scale usage; however, the different usage might not contribute significantly to gender differences in pain.

SIGNIFICANCE

There are differences in the usage of rating scales in which ratings for auditory, visual and noxious somatosensory stimuli are higher with NRS compared to VAS. Choosing a rating scale for research or clinical use should take this different item functioning into account.

Has the COVID-19 outbreak altered the prevalence of low back pain among physiotherapy students?

OBJECTIVE

To evaluate the prevalence of low back pain (LBP) among physiotherapy students during the COVID-19 lockdown in the State of Israel.

PARTICIPANTS/METHODS

One hundred and sixty four physiotherapy students from all four-year student levels were invited to participate. One hundred and thirty-seven students (83.5%) were recruited in the study with 79 females (57.7%) and 58 males (42.3%). We used a structured anonymous questionnaire that sought standard information on age, height, weight, sports activity and low back pain (LBP) prevalence during three periods.

RESULTS

No significant differences were noted in the prevalence of LBP between the lockdown period compared to 12-month period in all four-year levels. More so, our findings showed that LBP prevalence among physiotherapy students was greater during the 12-month period compared to the lifetime period.

CONCLUSIONS

This study indicates that COVID-19 lockdown has no negative impact on the prevalence of LBP among physiotherapy students.

The impact of sleep disturbance on pain perception: A systematic review examining the moderating effect of sex and age

Females have increased pain sensitivity and are more vulnerable to chronic pain conditions. Sleep disturbances are comorbid with chronic pain and exacerbate pain symptoms. Different types of sleep disturbance affect pain perception distinctly, but it is not clear if these effects are equal in men and women. This systematic review investigated potential differences in how sleep disturbance affects pain in males and females. We searched EBSCO, MEDLINE, Psych INFO, Science Direct, and Web of Science from January 2001 to November 2022 and found 38 studies with 978 participants. Separate random-effects models were used to estimate the pooled effect sizes based on standardized mean differences (SMDs) of experimental sleep disturbance paradigms on various pain outcomes. Sex moderated the effect of sleep disturbance on pain facilitation (SMD = 0.13; 95%CI: 0.004 to 0.022; p=.009) and pain inhibition (SMD = 0.033; 95%CI: 0.011 to 0.054; p=.005), with increased facilitation and decreased inhibition in females, but the opposite effect in males. Further, age moderated the effects of total sleep deprivation (SMD = -0.194; 95%CI -0.328 to -0.060; p=.008) on pain sensitivity and fragmented sleep (SMD = -0.110; 95%CI: 0.148 to -0.072; p<.001) on pain threshold. While the moderating effect of sex and age on the sleep-pain relationship was small, these factors need to be considered in future sleep-pain research.

Photobiomodulation Therapy on the Palliative Care of Temporomandibular Disorder and Orofacial/Cervical Skull Pain: Preliminary Results from a Randomized Controlled Clinical Trial

The main symptoms of temporomandibular disorders (TMDs) are pain from musculoskeletal and/or joint-in the head and neck region-and complaints of difficulty in mandibular movements. The photobiomodulation therapy (PBMT) has been reported as a promising treatment in the management of these symptoms. The objective of this research was to assess the effect of PBMT immediately after irradiation on TMDs symptoms under a prospective clinical trial, randomized, triple-blinded, placebo-controlled, and with two parallel arms. According to the RDC/TMD, maximum mouth opening (MMO) and pain in the orofacial/cervical muscles and temporomandibular joint (TMJ) were recorded. One hundred forty-five participants (71 placebo and 74 PBMT experimental) were analyzed after irradiation protocols (sham-PBMT or PBMT) at the orofacial/cervical skull musculature and at the TMJ. The results showed a reduction in the total pain score (p = 0.026), a reduction in the number of painful points (p = 0.013), and an increase in the MMO (p = 0.016) in the PBMT protocol group when compared to the placebo protocol (sham-PBMT). The PBMT was shown to be effective in reducing orofacial/cervical skull pain immediately after the irradiation. It is clinically relevant and should be taken into consideration by professionals who are dedicated to treating this pathology because, in addition to bringing comfort to patients who need dental treatment, it also consists of a low-cost and low technical complexity clinical approach.

Differing Effects of Nociception and Pain Memory on Isometric Muscle Strength in Participants With and Without a History of Injury: A Quasi-Experimental Study

OBJECTIVE

The goals of this study are to establish whether mechanical pressure pain, short-term memory recall of a painful stimulus, or long-term memory of a previous painful lower limb injury alters isometric muscle strength and whether there was a difference in responses between participants with and without a previous history of injury.

DESIGN

Fifty-nine pain-free participants (29 with previous injury and 30 without) participated in this study. Tibialis anterior isometric muscle strength was compared pre- and post-noxious mechanical stimulus with instructions to recall pain (short- and long-term).

RESULTS

Short- and long-term pain recall produced a significant reduction in muscle strength (short-term: F (1,57) = 160.472, P < 0.001; long-term: F (1,57) = 128.899, P < 0.001). A greater decrease was experienced with short- and long-term pain memory than exposure to mechanical pain (mechanical pain: -14.8% or -32.98 kg, 95% confidence interval [CI], -41.57 to -24.19; short-term: -24.1% or -52.70 kg, 95% CI = -60.98 to -44.34; long-term: -20.3% or -44.63 kg, 95% CI = -52.77 to -36.95). There was no significant difference in responses associated with an injury history.

CONCLUSIONS

Findings suggest that recalled pain memory can impact motor responses and calls attention to the role of past injury history in the rehabilitation process.

Changes in sex hormones and their interactions are related to pain perception between different menstrual subphases

Whether sex hormones are related to pain perception across the menstrual cycle is unclear. We examined changes in experimental pain perception in healthy young females between the early to midfollicular subphase (emF) and the midluteal subphase (mL) and explored the role of sex hormones. Sixty-six participants were involved in the study. We tested pressure pain, cold pain, ischemic pain, and needle pain, while at the same time we measured sex hormones levels in two menstrual subphases. Only the right ulna pressure test showed a significant reduction in pain threshold (PPTh3) during the mL. The absolute change of PPTh3 (PPTh3mL - PPTh3emF) was related to the absolute change of prolactin. The relative change of the range of pain tolerance for pressure pain of the right ulna (RPT3rc) was related to the relative change of progesterone (Prc) and estradiol (E2rc) levels, and the interaction effects showed that at Prc ≤ 30, E2rc was positively correlated with RPT3rc. The same, the relative change of pressure pain tolerance of the pulp of the middle finger on the right hand (PPTo4rc) was related to E2rc and Prc, and the results of the interaction between E2rc and Prc suggest that when E2rc is ≤0.8, Prc is positively correlated with PPTo4rc. Two different formulas were applied in this study and showed inconsistent results. Most pain tests showed no difference between the two subphases of the menstrual cycle. Only the relative changes of the PPTo4 and RPT3 are related to the E2rc and Prc, respectively, between menstrual subphases in an interactive way in healthy young women.

Pain chronification impacts whole-brain functional connectivity in women with hip osteoarthritis during pain stimulation

OBJECTIVE

Previous neuroimaging studies have shown that patients with chronic pain display altered functional connectivity across distributed brain areas involved in the processing of nociceptive stimuli. The aim of the present study was to investigate how pain chronification modulates whole-brain functional connectivity during evoked clinical and tonic pain.

METHODS

Patients with osteoarthritis of the hip (n = 87) were classified into 3 stages of pain chronification (Grades I-III, Mainz Pain Staging System). Electroencephalograms were recorded during 3 conditions: baseline, evoked clinical hip pain, and tonic cold pain (cold pressor test). The effects of both factors (recording condition and pain chronification stage) on the phase-lag index, as a measure of neuronal connectivity, were examined for different frequency bands.

RESULTS

In women, we found increasing functional connectivity in the low-frequency range (delta, 0.5-4 Hz) across pain chronification stages during evoked clinical hip pain and tonic cold pain stimulation. In men, elevated functional connectivity in the delta frequency range was observed in only the tonic cold pain condition.

CONCLUSIONS

Across pain chronification stages, we found that widespread cortical networks increase their synchronization of delta oscillations in response to clinical and experimental nociceptive stimuli. In view of previous studies relating delta oscillations to salience detection and other basic motivational processes, our results hint at these mechanisms playing an important role in pain chronification, mainly in women.

Cannabidiol modulates chronic neuropathic pain aversion behavior by attenuation of neuroinflammation markers and neuronal activity in the corticolimbic circuit in male Wistar rats

Chronic neuropathic pain (CNP) is a vast world health problem often associated with the somatosensory domain. This conceptualization is problematic because, unlike most other sensations that are usually affectively neutral and may present emotional, affective, and cognitive impairments. Neuronal circuits that modulate pain can increase or decrease painful sensitivity based on several factors, including context and expectation. The objective of this study was to evaluate whether subchronic treatment with Cannabidiol (CBD; 0.3, 3, and 10 mg/kg intraperitoneal route - i.p., once a day for 3 days) could promote pain-conditioned reversal, in the conditioned place preference (CPP) test, in male Wistar rats submitted to chronic constriction injury (CCI) of the sciatic nerve. Then, we evaluated the expression of astrocytes and microglia in animals treated with CBD through the immunofluorescence technique. Our results demonstrated that CBD promoted the reversal of CPP at 3 and 10 mg/kg. In CCI animals, CBD was able to attenuate the increase in neuronal hyperactivity, measured by FosB protein expression, in the regions of the corticolimbic circuit: anterior cingulate cortex (ACC), complex basolateral amygdala (BLA), granular layer of the dentate gyrus (GrDG), and dorsal hippocampus (DH) - adjacent to subiculum (CA1). CBD also prevented the increased expression of GFAP and IBA-1 in CCI animals. We concluded that CBD effects on CNP are linked to the modulation of the aversive component of pain. These effects decrease chronic neuronal activation and inflammatory markers in regions of the corticolimbic circuit.

Topical ophthalmic anesthetics for corneal abrasions

BACKGROUND

Despite potential analgesic benefits from topical ophthalmic amides and esters, their outpatient use has become of concern because of the potential for abuse and ophthalmic complications.

OBJECTIVES

To assess the effectiveness and safety of topical ophthalmic anesthetics compared with placebo or other treatments in persons with corneal abrasions.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE; Embase.com; Latin American and Caribbean Health Sciences (LILACS); ClinicalTrials.gov; and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP), without restriction on language or year of publication. The search was performed on 10 February 2023.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of topical ophthalmic anesthetics alone or in combination with another treatment (e.g. nonsteroidal anti-inflammatory drugs (NSAIDs)) versus a non-anesthetic control group (e.g. placebo, non-treatment, or alternative treatment). We included trials that enrolled participants of all ages who had corneal abrasions within 48 hours of presentation.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodology.

MAIN RESULTS

We included nine parallel-group RCTs with a total of 556 participants (median number of participants per study: 45, interquartile range (IQR) 44 to 74), conducted in eight countries: Australia, Canada, France, South Korea, Turkey, New Zealand, UK, and USA. Study characteristics and risk of bias Four RCTs (314 participants) investigated post-traumatic corneal abrasions diagnosed in the emergency department setting. Five trials described 242 participants from ophthalmology surgery centers with post-surgical corneal defects: four from photorefractive keratectomy (PRK) and one from pterygium surgery. Study duration ranged from two days to six months, the most common being one week (four RCTs). Treatment duration ranged from three hours to one week (nine RCTs); the majority were between 24 and 48 hours (five RCTs). The age of participants was reported in eight studies, ranging from 17 to 74 years of age. Only one participant in one trial was under 18 years of age. Of four studies that reported funding sources, none was industry-sponsored. We judged a high risk of bias in one trial with respect to the outcome pain control by 48 hours, and in five of seven trials with respect to the outcome complications at the furthest time point. The domain for which we assessed studies to be at the highest risk of bias was missing or selective reporting of outcome data. Findings The treatments investigated included topical anesthetics compared with placebo, topical anesthetic compared with NSAID (post-surgical cases), and topical anesthetics plus NSAID compared with placebo (post-surgical cases). Pain control by 24 hours In all studies, self-reported pain outcomes were on a 10-point scale, where lower numbers represent less pain. In post-surgical trials, topical anesthetics provided a moderate reduction in self-reported pain at 24 hours compared with placebo of 1.28 points on a 10-point scale (mean difference (MD) -1.28, 95% confidence interval (CI) -1.76 to -0.80; 3 RCTs, 119 participants). In the post-trauma participants, there may be little or no difference in effect (MD -0.04, 95% CI -0.10 to 0.02; 1 RCT, 76 participants). Compared with NSAID in post-surgical participants, topical anesthetics resulted in a slight increase in pain at 24 hours (MD 0.82, 95% CI 0.01 to 1.63; 1 RCT, 74 participants). One RCT compared topical anesthetics plus NSAID to placebo. There may be a large reduction in pain at 24 hours with topical anesthetics plus NSAID in post-surgical participants, but the evidence to support this large effect is very uncertain (MD -5.72, 95% CI -7.35 to -4.09; 1 RCT, 30 participants; very low-certainty evidence). Pain control by 48 hours Compared with placebo, topical anesthetics reduced post-trauma pain substantially by 48 hours (MD -5.68, 95% CI -6.38 to -4.98; 1 RCT, 111 participants) but had little to no effect on post-surgical pain (MD 0.41, 95% CI -0.45 to 1.27; 1 RCT, 44 participants), although the evidence is very uncertain. Pain control by 72 hours One post-surgical RCT showed little or no effect of topical anesthetics compared with placebo by 72 hours (MD 0.49, 95% CI -0.06 to 1.04; 44 participants; very low-certainty evidence). Proportion of participants with unresolved epithelial defects When compared with placebo or NSAID, topical anesthetics increased the number of participants without complete resolution of defects in trials of post-trauma participants (risk ratio (RR) 1.37, 95% CI 0.78 to 2.42; 3 RCTs, 221 participants; very low-certainty evidence). The proportion of placebo-treated post-surgical participants with unresolved epithelial defects at 24 to 72 hours was lower when compared with those assigned to topical anesthetics (RR 0.14, 95% CI 0.01 to 2.55; 1 RCT, 30 participants; very low-certainty evidence) or topical anesthetics plus NSAID (RR 0.33, 95% CI 0.04 to 2.85; 1 RCT, 30 participants; very low-certainty evidence). Proportion of participants with complications at the longest follow-up When compared with placebo or NSAID, topical anesthetics resulted in a higher proportion of post-trauma participants with complications at up to two weeks (RR 1.13, 95% CI 0.23 to 5.46; 3 RCTs, 242 participants) and post-surgical participants with complications at up to one week (RR 7.00, 95% CI 0.38 to 128.02; 1 RCT, 44 participants). When topical anesthetic plus NSAID was compared with placebo, no complications were reported in either treatment arm up to one week post-surgery (risk difference (RD) 0.00, 95% CI -0.12 to 0.12; 1 RCT, 30 participants). The evidence is very uncertain for safety outcomes. Quality of life None of the included trials assessed quality of life outcomes.

AUTHORS' CONCLUSIONS

Despite topical anesthetics providing excellent pain control in the intraoperative setting, the currently available evidence provides little or no certainty about their efficacy for reducing ocular pain in the initial 24 to 72 hours after a corneal abrasion, whether from unintentional trauma or surgery. We have very low confidence in this evidence as a basis to recommend topical anesthetics as an efficacious treatment modality to relieve pain from corneal abrasions. We also found no evidence of a substantial effect on epithelial healing up to 72 hours or a reduction in ocular complications when we compared anesthetics alone or with NSAIDs versus placebo.

Spanish version of the pain beliefs questionnaire: Translation, cross-cultural adaptation, validation, and psychometric properties in a working population

BACKGROUND

Chronic musculoskeletal pain is a major health problem and a common cause of disability in the workplace. Beliefs related to musculoskeletal pain may influence its onset and perpetuation. Consequently, tools designed to identify potentially harmful beliefs are needed. However, the Pain Beliefs Questionnaire (PBQ) is not available for individuals speaking European-Spanish.

OBJECTIVES

To translate and culturally adapt the original English version of the PBQ into European-Spanish and evaluate its psychometric properties among Spanish workers with and without chronic musculoskeletal pain.

DESIGN

Study on measurement properties.

METHODS

A translation and cultural adaptation process was based on a forward-backward translation process. One hundred fifty-one active workers were included. Participants completed the PBQ (composed of the organic and psychological subscales), the Pain Catastrophizing Scale (PCS), and the Hospital Anxiety and Depression Scale (HADS). Finally, thirty participants completed the PBQ again two weeks later for test-retest reliability.

RESULTS

The PBQ showed adequate internal consistency (Cronbach's alpha: 0.72-0.73), good item response stability (weighted Kappa: 0.65-0.90), and reliability (Intraclass Correlation Coefficient: 0.72-0.80). A positive correlation was found between the PCS and the organic subscale (r = 0.403). However, no significant correlations were found between the HADS and the PBQ subscales. Workers with chronic musculoskeletal pain showed greater scores in the organic subscale and lower scores in the psychological subscale than workers without pain.

CONCLUSION

The Spanish version of the PBQ was linguistically accurate and acceptable for use by workers with and without musculoskeletal pain.

Association between early nonpharmacological management and follow-up for low back pain in the veterans health administration

Background

Low back pain (LBP) is a common reason individuals seek healthcare. Nonpharmacologic management (NPM) is often recommended as a primary intervention, and earlier use of NPM for LBP shows positive clinical outcomes. Our purpose was to evaluate how timing of engagement in NPM for LBP affects downstream LBP visits during the first year.

Methods

This study was a secondary analysis of an observational cohort study of national electronic health record data. Patients entering the Musculoskeletal Diagnosis/Complementary and Integrative Health Cohort with LBP from October 1, 2016 to September 30, 2017 were included. Exclusive patient groups were defined by engagement in NPM within 30 days of entry ("very early NPM"), between 31 and 90 days ("early NPM"), or not within the first 90 days ("no NPM"). The outcome was time, in days, to the final LBP follow-up after 90 days and within the first year. Cox proportional hazards regression was used to model time to final follow up, controlling for additional demographic and clinical covariables.

Results

The study population included 44,175 patients, with 16.7% engaging in very early NPM and 13.1% in early NPM. Patients with very early NPM (5.2 visits, SD=4.5) or early NPM (5.7 visits, SD=4.6) had a higher mean number of LBP visits within the first year than those not receiving NPM in the first 90 days (3.2 visits, SD = 2.5). The very early NPM (HR=1.50, 95% CI: 1.46-1.54; median=48 days, IQR=97) and early NPM (HR=1.27, 95% CI: 1.23-1.30; median=88 days, IQR=92) had a significantly shorter time to final follow-up than the no NPM group (median=109 days, IQR=150).

Conclusions

Veterans Health Administration patients receiving NPM for LBP within the first 90 days after initially seeking care demonstrate a significantly faster time to final follow-up visit within the first year compared to those who do not.

Connecting dots in disorders of gut-brain interaction: the interplay of stress and sex hormones in shaping visceral pain

Visceral pain and stress are tightly intertwined bodily and emotional phenomena, which enable a flexible adaptation to environmental challenges by activating a response repertoire to restore homeostasis along the gut-brain axis. However, visceral pain and stress can persist widely independent of the initial cause, acquiring independent disease values and posing major health burdens as predominant features in disorders of gut-brain interaction (DGBI). Epidemiological data consistently documents an increased prevalence for women to suffer from chronic visceral pain, possibly shaped by sex hormones and modulated by stress and its biological and psychosocial correlates. Yet, mechanisms underlying the complex interactions between altered visceroception, stress and sex remain widely elusive, especially in clinical populations with DGBI. We herein selectively review mechanisms of interactions between stress and sex in the complex pathophysiology of DGBI. A particular emphasis is laid on visceral pain, in which stress constitutes a major risk factor as well as mediator, and sex-related differences are particularly pronounced. Building on the neurobiology of stress and mechanisms of gut-brain interactions, we highlight putative target mechanisms via which visceral pain and stress may converge with sex effects into a triad. Accommodating a global demographic shift, we propose a lifespan perspective in future research, which may enable a more fine-tuned evaluation of this complex interplay exerting distinct challenges during vulnerable developmental phases. This viewpoint may advance our understanding of pathophysiological processes and can ultimately inspire novel tailored prevention strategies and therapeutic approaches in the treatment of chronic visceral pain and DGBI across the lifespan.

Neurophysiological and Psychosocial Mechanisms of Fibromyalgia: A Comprehensive Review and Call for An Integrative Model

Research into the neurobiological and psychosocial mechanisms involved in fibromyalgia has progressed remarkably in recent years. Despite this, current accounts of fibromyalgia fail to capture the complex, dynamic, and mutual crosstalk between neurophysiological and psychosocial domains. We conducted a comprehensive review of the existing literature in order to: a) synthesize current knowledge on fibromyalgia; b) explore and highlight multi-level links and pathways between different systems; and c) build bridges connecting disparate perspectives. An extensive panel of international experts in neurophysiological and psychosocial aspects of fibromyalgia discussed the collected evidence and progressively refined and conceptualized its interpretation. This work constitutes an essential step towards the development of a model capable of integrating the main factors implicated in fibromyalgia into a single, unified construct which appears indispensable to foster the understanding, assessment, and intervention for fibromyalgia.

Prospective paired crossover evaluation of potential impact of investigator gender on perceived pain intensity early after acute or scheduled surgery

BACKGROUND

Postoperative pain is common but often difficult to assess, and there are many potential confounders. Over the last decades, the gender of investigator as well as participant has been found to influence pain perception in both preclinical and clinical studies. However, to our knowledge this has not been studied in various postoperative patients. Objectives of this study were to test the hypotheses that pain intensity levels early after acute or scheduled in- or out-hospital surgery are lower when evaluated by a female investigator, and higher when reported by a female patient.

METHODS

In this prospective observational paired crossover study, two investigators of opposite genders independently obtained individually reported pain intensity levels with a visual analogue scale in a mixed cohort of adult postoperative study patients at Skåne University Hospital in Malmö, Sweden.

RESULTS

In total, 245 (129 female) study patients were included and then one female excluded. The study patients rated their intensity of postoperative pain lower when evaluated by a female than by a male investigator (P = 0.006), where the male patients constituted the significant difference (P < 0.001). Pain intensity levels did not differ between female and male study patients (P = 0.210).

CONCLUSIONS

Main findings of lower pain intensity reported by males to a female than to a male investigator early after surgery in this paired crossover study in mixed postoperative patients, indicate that potential impact of investigator gender on pain perception should be considered and further evaluated in clinical bedside practice. Trial registration Retrospectively registered in the ClinicalTrials.gov research database on 24th June 2019 with TRN number NCT03968497.

Sex differences in migraine attack characteristics: A longitudinal E-diary study

OBJECTIVE

In this prospective cohort study, characteristics of perimenstrual and non-perimenstrual migraine attacks in women were compared with migraine attacks in men.

BACKGROUND

Women report longer migraine attacks and more accompanying symptoms than men in cross-sectional questionnaire studies, but this has not been confirmed in longitudinal studies. Supposed differences could result from different characteristics specific to perimenstrual migraine attacks, or of attacks in women in general.

METHODS

This cohort study was performed among patients with migraine who were treated at the Leiden Headache Clinic. We assessed differences in migraine attack characteristics between men and women who were prospectively followed by a previously validated electronic headache diary. The primary outcome was "attack" duration. Differences between perimenstrual (Days -2 to +3 of the menstrual cycle) and non-perimenstrual attacks in women versus attacks in men were corrected for age, chronic migraine, and medication overuse headache.

RESULTS

A total of 1347 women and 284 men were included, reflecting the preponderance of women in migraine prevalence. Crude median (first and third quartile [Q1-Q3]) attack duration in men was 32.1 [17.7-53.6] h, compared to 36.7 [21.9-62.4] h for non-perimenstrual migraine attacks and 44.4 [17.9-79.0] h for perimenstrual migraine attacks in women. After correction for confounding, perimenstrual migraine attacks were 1.62 (95% confidence interval [CI] 1.47-1.79; p < 0.001) and non-perimenstrual 1.15 (95% CI 1.05-1.25; p = 0.003) times longer compared to migraine attacks in men. The mean relapse percentage in men was 9.2%, compared to 12.6% for non-perimenstrual migraine attacks, and 15.7% for perimenstrual migraine attacks. Relapse risk was greater for perimenstrual (odds ratio [OR] 2.39, 95% CI 1.93-2.95; p < 0.001), but not for non-perimenstrual (OR 1.18, 95% CI 0.97-1.45; p = 0.060) attacks. Migraine attacks in women were more often accompanied by photophobia, phonophobia, and nausea, but less often aura.

CONCLUSION

Compared to attacks in men, both perimenstrual and non-perimenstrual migraine attacks are of longer duration and are more often accompanied by associated symptoms. A sex-specific approach to migraine treatment and research is needed.

A nationwide survey on producer and veterinarian perceptions of the painfulness of procedures and disease states in dairy and beef cattle

Failure to adequately manage pain in cattle causes suffering and is thus a welfare concern for the livestock industry. The objectives of this study were to summarize caregiver perceptions of the painfulness of various procedures and disease conditions in cattle. This survey also assessed factors that impact the perception of painfulness and determined relationships between pain perception and mitigation in producers and veterinarians in the United States beef and dairy cattle industries. An online survey was distributed via organization listservs and social media groups representing beef and dairy veterinarians and producers. The survey included questions about respondent demographics and pain perception and frequency of pain mitigation use for a variety of common husbandry procedures and disease conditions in cattle less than 2 months, 2-12 months, and greater than 12 months of age. Descriptive statistics were generated, and ordinal logistic regressions were used to assess the relationship between perceived pain level, frequency of pain mitigation use, and respondent demographic factors (e.g., gender, age, and role). There was a relatively low percentage of respondents that identified there was "no pain" associated with the listed procedures and conditions. Across the majority of procedures and conditions and cattle age categories, men perceived procedures to be less painful than women (P < 0.05). Veterinarians and producer-veterinarians perceived procedures to be more painful than producers (P < 0.05) for the majority of procedures and conditions. There were some differences identified between respondent age groups in pain perception but the trends were not consistent across procedures and conditions. There was a significant positive linear trend, with greater perceived pain associated with greater likelihood of providing local and systemic analgesia for all procedures and conditions across all cattle age categories (P ≤ 0.02). Perception of pain is complex and multifactorial, and it influences the likelihood to treat pain in cattle. This research highlighted the importance of understanding how these factors may play a role in increasing the use of pain mitigation within the beef and dairy industries.

Prevalence of pain and its treatment among older adults in India: a nationally representative population-based study

ABSTRACT

There were no estimates of the prevalence of pain and its treatment in the older population of India obtained from face-to-face interviews with a nationally representative sample. We addressed this evidence gap by using data on 63,931 individuals aged 45 years and older from the 2017/2018 Longitudinal Ageing Study in India. We identified pain from an affirmative response to the question: Are you often troubled by pain? We also identified those who reported pain that limited usual activities and who received treatment for pain. We estimated age- and sex-adjusted prevalence of pain, pain limiting usual activity and treatment, and compared these estimates across states and sociodemographic groups. We used a multivariable probit model to estimate full adjusted differences in the probability of each outcome across states and sociodemographic groups. We estimated that 36.6% (95% confidence interval [CI]: 35.3-37.8) of older adults in India were often troubled by pain and 25.2% (95% CI: 24.2-26.1) experienced pain limiting usual activity. We estimated that 73.3% (95% CI: 71.9-74.6) of those often troubled by pain and 76.4% (95% CI: 74.9-78.0) of those with pain that limited usual activity received treatment. There was large variation in each outcome across states. Fully adjusted prevalence of pain and pain limiting usual activity were higher among individuals who were female, older, less educated, rural residents, and poorer. Prevalence of treatment among those troubled by pain was lower among socially disadvantaged groups.

Prevalence of and factors associated with unmanageable pain levels in people with knee or hip osteoarthritis: a cross-sectional population-based study

BACKGROUND

Pain due to knee and / or hip osteoarthritis (HKOA) is the most common symptom for seeking healthcare. Pain interferes on daily activities, social and occupational participation in people with HKOA. The goal of this study is to estimate the prevalence of unmanageable pain levels (UPL) among people with HKOA), characterize this population and identify factors associated with UPL, and compare therapeutic strategies used by people with UPL versus manageable pain levels (MPL).

METHODS

We analysed data from the EpiReumaPt study (n = 10,661), that included a representative sample of the Portuguese population. Among these, 1081 participants had a validated diagnosis of HKOA by a rheumatologist.. Sociodemographic, lifestyle and health-related data were collected in a structured interview. Pain intensity (NPRS) data were collected in a medical appointment. Painmedication (last month), physiotherapy and surgery were considered as therapies for pain management. UPL was defined as a mean pain intensity in the previous week of ≥5 points on 11-point numeric pain rating scale. The factors associated with UPL were analyzed with logistic regression (p < 0.05, 95%CI). The effect of unmanageable pain levels was assessed by the HOOS/KOOS activities of daily living and quality of life subscales. Symptoms of anxiety and depression were assessed by the Hospital Anxiety and Depression Scale (HADS). Analysis was completed with linear and logistic regression. All analysis were weighted.

RESULTS

The estimated prevalence of UPL among people with HKOA was 68.8%. UPL was associated with being female (odds ratio (OR) = 2.36, p < 0.001), being overweight (OR = 1.84, p = 0.035) or obese (OR = 2.26, p = 0.006), and having multimorbidity (OR = 2.08, p = 0.002). People with UPL reported worse performance in activities of daily living and lower quality of life (β = - 21.28, p < 0.001 and β = - 21.19, p < 0.001, respectively) than people with MPL. People with UPL consumed more NSAIDs (22.0%, p = 0.003), opioids (4.8%, p = 0.008), paracetamol (2.7%, p = 0.033), and overall analgesics (7.3%, p = 0.013) than people with MPL. A higher proportion of people with UPL underwent physiotherapy (17.5%, p = 0.002) than people with MPL.

CONCLUSION

Two-thirds of people with HKOA in Portugal have poor management of their pain levels. Clinical and lifestyle factors, that are highly presented in individuals with HKOA, are associated with unmanageable pain. Our results highlighting the need for further research and implementation of effective interventions to improve pain, function and quality of life in people with HKOA.

Pain and aging: A unique challenge in neuroinflammation and behavior

Chronic pain is one of the most common, costly, and potentially debilitating health issues facing older adults, with attributable costs exceeding $600 billion annually. The prevalence of pain in humans increases with advancing age. Yet, the contributions of sex differences, age-related chronic inflammation, and changes in neuroplasticity to the overall experience of pain are less clear, given that opposing processes in aging interact. This review article examines and summarizes pre-clinical research and clinical data on chronic pain among older adults to identify knowledge gaps and provide the base for future research and clinical practice. We provide evidence to suggest that neurodegenerative conditions engender a loss of neural plasticity involved in pain response, whereas low-grade inflammation in aging increases CNS sensitization but decreases PNS sensitivity. Insights from preclinical studies are needed to answer mechanistic questions. However, the selection of appropriate aging models presents a challenge that has resulted in conflicting data regarding pain processing and behavioral outcomes that are difficult to translate to humans.

Does the pain sensitivity questionnaire correlate with tourniquet pain in patients undergoing ankle surgery?

Background

Tourniquet pain is the most prominent problem in ankle surgery, and there is no proper method to predict it. It was reported that pain sensitivity questionnaires could evaluate the pain sensitivity of subjects. Its potential to predict tourniquet pain in ankle surgery is constructive and meaningful.

Methods

One hundred and twenty patients undergoing ankle surgery were included in this study. The pain sensitivity questionnaire (PSQ) and self-rating anxiety scale (SAS) were completed before the operation. The methods included an ultrasound-guided popliteal sciatic, a femoral nerve block, and a proximal thigh tourniquet. The pressure of the tourniquet was set according to the systolic blood pressure (SBP + 100 mmHg). A visual analogue scale (VAS) was used to assess the tourniquet pain. Also, the onset time of tourniquet pain ≥4 VAS units was recorded.

Results

The PSQ-total and PSQ-minor scores were significantly correlated with the onset time when the tourniquet pain ≥4 VAS units (r = -0.763, r = -0.731, P < 0.001). The PSQ-total score <6.5 group gave significantly lower ratings for items 3, 4, 14, and 16 in the PSQ survey compared to the PSQ-total score ≥6.5 group (P < 0.05). Patients with high pain sensitivity have a higher need for analgesic drugs (P < 0.001). PSQ-total score ≥6.5 (OR = 185.8, 95% CI = 39.8-1,437.6, P < 0.001), sex (male, OR = 0.11, 95% CI = 0.018-0.488, P < 0.05), and age (OR = 0.92, 95% CI = 0.842-0.995, P < 0.05) were risk factors for reporting a tourniquet pain ≥4 VAS units within 30 min.

Conclusion

The PSQ score is found to be correlated with intraoperative tourniquet pain. In addition, sex and age also affect the time of having intraoperative tourniquet pain.

Can we characterize A-P/IAP behavioural phenotypes in people with chronic pain?

Two behavioural phenotypes in healthy people have been delineated based on their intrinsic attention to pain (IAP) and whether their reaction times (RT) during a cognitively-demanding task are slower (P-type) or faster (A-type) during experimental pain. These behavioural phenotypes were not previously studied in chronic pain populations to avoid using experimental pain in a chronic pain context. Since pain rumination (PR) may serve as a supplement to IAP without needing noxious stimuli, we attempted to delineate A-P/IAP behavioural phenotypes in people with chronic pain and determined if PR can supplement IAP. Behavioural data acquired in 43 healthy controls (HCs) and 43 age-/sex-matched people with chronic pain associated with ankylosing spondylitis (AS) was retrospectively analyzed. A-P behavioural phenotypes were based on RT differences between pain and no-pain trials of a numeric interference task. IAP was quantified based on scores representing reported attention towards or mind-wandering away from experimental pain. PR was quantified using the pain catastrophizing scale, rumination subscale. The variability in RT was higher during no-pain trials in the AS group than HCs but was not significantly different in pain trials. There were no group differences in task RTs in no-pain and pain trials, IAP or PR scores. IAP and PR scores were marginally significantly positively correlated in the AS group. RT differences and variability were not significantly correlated with IAP or PR scores. Thus, we propose that experimental pain in the A-P/IAP protocols can confound testing in chronic pain populations, but that PR could be a supplement to IAP to quantify attention to pain.

Psychosocial resources predict frequent pain differently for men and women: A prospective cohort study

INTRODUCTION

Psychosocial resources, psychological and social factors like self-efficacy and social support have been suggested as important assets for individuals with chronic pain, but the importance of psychosocial resources for the development of pain is sparsely examined, especially sex and gender differences. The aim of this study was to investigate associations between psychosocial resources and sex on the development of frequent pain in a general population sample, and to deepen the knowledge about sex and gender patterns.

METHODS

A sample from the Swedish Health Assets Project, a longitudinal cohort study, included self-reported data from 2263 participants, 53% women, with no frequent pain at baseline. The outcome variable was frequent pain at 18-months follow-up. Psychosocial resources studied were general self-efficacy, instrumental and emotional social support. Log binomial regressions in a generalised linear model were used to calculate risk ratios (RRs), comparing all combinations of men with high psychosocial resources, men with low psychosocial resources, women with high psychosocial resources and women with low psychosocial resources.

RESULTS

Women with low psychosocial resources had higher risk of frequent pain at follow-up compared to men with high resources: general self-efficacy RR 1.82, instrumental social support RR 2.33 and emotional social support RR 1.94. Instrumental social support was the most important protective resource for women, emotional social support was the most important one for men. Results were discussed in terms of gender norms.

CONCLUSIONS

The psychosocial resources general self-efficacy, instrumental and emotional support predicted the risk of developing frequent pain differently among and between men and women in a general population sample. The results showed the importance of studying sex and gender differences in psychological and not least social predictors for pain.

Diffusion tensor imaging reveals sex differences in pain sensitivity of rats

Studies on differences in brain structure and function according to sex are reported to contribute to differences in behavior and cognition. However, few studies have investigated brain structures or used tractography to investigate gender differences in pain sensitivity. The identification of tracts involved in sex-based structural differences that show pain sensitivity has remained elusive to date. Here, we attempted to demonstrate the sex differences in pain sensitivity and to clarify its relationship with brain structural connectivity. In this study, pain behavior test and brain diffusion tensor imaging (DTI) were performed in male and female rats and tractography was performed on the whole brain using fiber tracking software. We selected eight brain regions related to pain and performed a tractography analysis of these regions. Fractional anisotropy (FA) measurements using automated tractography revealed sex differences in the anterior cingulate cortex (ACC)-, prefrontal cortex (PFC)-, and ventral posterior thalamus-related brain connections. In addition, the results of the correlation analysis of pain sensitivity and DTI tractography showed differences in mean, axial, and radial diffusivities, as well as FA. This study revealed the potential of DTI for exploring circuits involved in pain sensitivity. The behavioral and functional relevance's of measures derived from DTI tractography is demonstrated by their relationship with pain sensitivity.

Exploring the contributions of sex and traditionally genderized interpersonal-expressive traits to variability in post-trauma pain ratings

OBJECTIVES

Multiple intra- and inter-individual variabilities sculpt the experience of pain. However, integration of sex and gender has been under-explored in explanatory models of pain. This study aimed to examine the role of sex and traditionally genderized interpersonal-expressive traits, and their interactions in explaining the variability of pain ratings.

METHODS

Data from 113 participants following acute non-catastrophic musculoskeletal (MSK) injuries were included. Participants completed the Brief Pain Inventory (BPI) and the Gender, Pain and Expectations Scale (GPES). An independent T-test was used to compare differences in BPI subscales between the sexes. Pearson correlations explored the associations between BPI and GPES subscale scores for the overall sample and also for the sample when disaggregated by sex. Multiple linear regression was used to investigate the interaction of sex and gender traits in explaining the BPI scores.

RESULTS

No differences were found between the sexes in mean BPI Severity and Interference. Across sexes, Relationship-oriented was positively associated with greater BPI Severity (r = 0.20) and Emotive was positively associated with BPI Interference (r = 0.24). In sex-disaggregated analyses, these associations were significant in females only. Goal-oriented was associated with neither BPI Severity nor Interference. In multivariate regression, only Emotive was a significant predictor of BPI Interference.

DISCUSSION

The findings suggest that variances in pain-related interference are partially explained by scores on a scale measuring self-perceptions of Emotive qualities. Sex was not predictive of either pain outcome in both bivariate and multivariate analyses. Researchers and clinicians are encouraged to consider both sex- and gender-based variables when interpreting patient pain reports.

Data-Driven Path Analytic Modeling to Understand Underlying Mechanisms in COVID-19 Survivors Suffering from Long-Term Post-COVID Pain: A Spanish Cohort Study

Pain can be present in up to 50% of people with post-COVID-19 condition. Understanding the complexity of post-COVID pain can help with better phenotyping of this post-COVID symptom. The aim of this study is to describe the complex associations between sensory-related, psychological, and cognitive variables in previously hospitalized COVID-19 survivors with post-COVID pain, recruited from three hospitals in Madrid (Spain) by using data-driven path analytic modeling. Demographic (i.e., age, height, and weight), sensory-related (intensity or duration of pain, central sensitization-associated symptoms, and neuropathic pain features), psychological (anxiety and depressive levels, and sleep quality), and cognitive (catastrophizing and kinesiophobia) variables were collected in a sample of 149 subjects with post-COVID pain. A Bayesian network was used for structural learning, and the structural model was fitted using structural equation modeling (SEM). The SEM model fit was excellent: RMSEA < 0.001, CFI = 1.000, SRMR = 0.063, and NNFI = 1.008. The only significant predictor of post-COVID pain was the level of depressive symptoms (β=0.241, p = 0.001). Higher levels of anxiety were associated with greater central sensitization-associated symptoms by a magnitude of β=0.406 (p = 0.008). Males reported less severe neuropathic pain symptoms (−1.50 SD S-LANSS score, p < 0.001) than females. A higher level of depressive symptoms was associated with worse sleep quality (β=0.406, p < 0.001), and greater levels of catastrophizing (β=0.345, p < 0.001). This study presents a model for post-COVID pain where psychological factors were related to central sensitization-associated symptoms and sleep quality. Further, maladaptive cognitions, such as catastrophizing, were also associated with depression. Finally, females reported more neuropathic pain features than males. Our data-driven model could be leveraged in clinical trials investigating treatment approaches in COVID-19 survivors with post-COVID pain and can represent a first step for the development of a theoretical/conceptual framework for post-COVID pain.

Sex-related differences in experimental pain sensitivity in subjects with painful or painless neuropathy after surgical repair of traumatic nerve injuries

Higher pain intensities at all experimental stimuli but a tendency to faster recovery after cold conditioning stimuli were seen in women with neuropathy in comparison with men.

Introduction:

Sex-related influences represent a contributor to greater pain sensitivity and have a higher prevalence of many chronic pain conditions, including neuropathic pain (NP), among women.

Objectives:

The aim was to analyze how differences in ongoing pain, experimental pain intensity, and conditioned pain modulation (CPM) relate to sex in subjects with neuropathy after traumatic nerve injuries.

Methods:

Endogenous pain modulation was compared between male (n = 77) and female (n = 55) subjects and between subjects with NP (female = 31, male = 39) and pain-free subjects with posttraumatic neuropathy (female = 24, male = 38). Conditioned pain modulation was assessed by pain ratings to pressure stimuli before and after a noxious conditioning stimulus (CS) conducted with one arm submerged in cold water (4°C) for 1 minute. Time of recovery (Time off) of pain intensity from peak VAS_maxc after CS was recorded and compared between male and female patients.

Results:

Greater ongoing pain intensity was found among female patients compared with male patients and more experimental pain after pressure and cold induced pain. Summing all groups together, women had 0.8 times higher odds (20%) of recovering sooner than men after CS (95% CI = 0.65–2.9). No differences in CPM, time off, and psychosocial variables were seen between female and male patients (P < 0.05).

Conclusion:

Our hypothesis for sex differences in endogenous pain modulation was only supported by a shorter after-sensation time after cold CS in female patients. No sex differences in the magnitude of CPM effect were identified. Increased pain intensity for experimental pain, in both neuropathic pain and neuropathy without pain, was found in female patients.

Sex-Related Effects of Adrenergic Drugs on Conditioned Pain Modulation: A Randomized Controlled Cross-Over Double-Blind Trial

Objective

Endogenous pain inhibition can be investigated using conditioned pain modulation (CPM). CPM efficacy has been reported to be influenced by various factors, such as gender and cardiovascular (autonomic) activity. The aim of this study is to describe the effect of pharmacological manipulations of autonomic activity on CPM efficacy.

Methods

Thirty healthy participants were enrolled to assess CPM efficacy in 4 experimental sessions. The first session consisted of the determination of baseline CPM effectiveness. The three following sessions were performed in a randomized order and consisted of the injection of (1) esmolol, (2) ephedrine, or (3) placebo, before the conditioning stimulus. Pain intensity induced by using a contact heat stimulation thermode was compared before and after a cold-pressure conditioning stimulus to evaluate CPM effectiveness.

Results

Our results show that inhibiting sympathetic nervous activity with esmolol did not have a significant effect on CPM. Conversely, enhancing sympathetic nervous activity with ephedrine increased CPM effectiveness in healthy women but decreased it in men.

Conclusions

Increasing sympathetic activity with adrenergic agonists, such as ephedrine, could improve CPM effectiveness in women. It will be interesting to verify if the same results are present in patients suffering from chronic pain and if adrenergic agonists could have better therapeutic effects in women showing reduced CPM effectiveness.

Treatments for kinesiophobia in people with chronic pain: A scoping review

Kinesiophobia is associated with pain intensity in people suffering from chronic pain. The number of publications highlighting this relationship has increased significantly in recent years, emphasizing the importance of investigating and synthesizing research evidence on this topic. The purpose of this scoping review was to answer the following questions: (1) What types of interventions have been or are currently being studied in randomized controlled trials (RCTs) for the management of kinesiophobia in patients with chronic pain? (2) What chronic pain conditions are targeted by these interventions? (3) What assessment tools for kinesiophobia are used in these interventions? According to the studies reviewed, (1) physical exercise is the most commonly used approach for managing irrational fear of movement, (2) interventions for kinesiophobia have primarily focused on musculoskeletal pain conditions, particularly low back pain and neck pain, and (3) the Tampa Scale of Kinesiophobia is the most commonly used tool for measuring kinesiophobia. Future RCTs should consider multidisciplinary interventions that can help patients confront their irrational fear of movement while taking into account the patient’s personal biological, psychological, and social experiences with pain and kinesiophobia.

Pain Extent Is Not Associated with Sensory-Associated Symptoms, Cognitive or Psychological Variables in COVID-19 Survivors Suffering from Post-COVID Pain

We aimed to investigate the relationship between pain extent, as a sign of sensitization, and sensory-related, cognitive and psychological variables in hospitalized COVID-19 survivors with post-COVID pain. One hundred and forty-six (67 males, 79 females) previously hospitalized COVID-19 survivors with post-COVID pain completed demographic (age, sex, height, weight), sensory-related (Central Sensitization Inventory, Self-Report Leeds Assessment of Neuropathic Symptoms), cognitive (Pain Catastrophizing Scale, Tampa Scale for Kinesiophobia) and psychological (Hospital Anxiety and Depression Scale, Pittsburgh Sleep Quality Index) variables. Pain extent and frequency maps were calculated from pain drawings using customized software. After conducting a correlation analysis to determine the relationships between variables, a stepwise linear regression model was performed to identify pain extent predictors, if available. Pain extent was significantly and weakly associated with pain intensity (r = −0.201, p = 0.014): the larger the pain extent, the lower the pain intensity. No other significant association was observed between pain extent and sensory-related, cognitive, or psychological variables in individuals with post-COVID pain. Females had higher pain intensity, more sensitization-associated symptoms, higher anxiety, lower sleep quality, and higher kinesiophobia levels than males. Sex differences correlation analyses revealed that pain extent was associated with pain intensity in males, but not in females. Pain extent was not associated with any of the measured variables and was also not related to the presence of sensitization-associated symptoms in our sample of COVID-19 survivors with long-term post-COVID pain.

Stigma and Chronic Pain

Stigma is defined by the World Health Organization (WHO) as "a mark of shame, disgrace or disapproval that results in an individual being rejected, discriminated against and excluded from participating in a number of different areas of society". Extensive literature searches have documented stigma in the context of health. Among the physical health conditions that are associated with stigma, chronic pain deserves particular attention. Stigma experienced by individuals with chronic pain affects their entire life. Literature identifies multiple dimensions or types of stigma, including public stigma, structural stigma and internalized stigma. Recent literature supports the biopsychosocial model of pain, according to which biological, psychological and sociocultural variables interact in a dynamic manner to shape an individual's response to chronic pain. Chronic pain affects a higher proportion of women than men around the world. There is an inadequate education of health care professionals regarding pain assessment and their insecurity to manage patients with chronic pain. A first-line intervention strategy could be to promote pain education and to expand knowledge and assessment of chronic pain, as recently highlighted for headache disorders, paradigmatically for resistant or refractory migraine, whose diagnosis, without an adequate education to understand the possible fluctuations of the disease, may have profound psychological implications with the idea of insolvability and contribute to stigmatizing the patient.

Intra-rater and inter-rater reliability of pressure pain threshold assessment in stroke patients

BACKGROUND

As pain is a common symptom following a stroke, pressure pain threshold (PPT) assessment can be used to evaluate pain status or pain sensitivity of patients. However, the reliability of PPT test in stroke patients is still unknown.

AIM

To examine the intra- and inter-rater reliability of PPT measurements in poststroke survivors and explore their factors.

DESIGN

An observational study.

SETTING

The setting of the study is a rehabilitation hospital.

POPULATION

The population of the study was represented by a total of 54 patients after stroke.

METHODS

The study included 16 measured points on the affected and unaffected sides. PPT was assessed by two raters in turn. Intra- and inter-rater reliability was evaluated by intraclass correlation coefficients (ICC).

RESULTS

All intra-rater (ICC=0.84-0.97) and inter-rater (ICC=0.83-0.95) reliability for PPT assessment were good or excellent in stroke patients. Of the 16 points, 12 showed higher intra-rater ICC values than inter-rater, whereas no evident difference was observed between the affected and unaffected sides. Furthermore, patients who were male, ischemic, or with higher motor function generally performed higher ICC values than those who were female (24 out of 32 results), hemorrhagic (28 out of 32 results), or mobility dysfunction (26 out of 32 results), respectively.

CONCLUSIONS

PPT assessment with good or excellent reliability can be used in stroke patients. Neither of the two sides (affected or unaffected) affects PPT reliability, and intra-rater reliability is better than inter-rater reliability. In addition, gender, stroke type, and motor function can affect the reliability of measuring mechanical pain threshold in poststroke survivors.

CLINICAL REHABILITATION IMPACT

The pressure algometer can be used as a reliable and portable tool to assess the mechanical pain tolerance and sensory function in stroke patients in clinics.

Sex and gender differences in pain

Chronic pain affects 20% of adults and is one of the leading causes of disability worldwide. Women and girls are disproportionally affected by chronic pain. About half of chronic pain conditions are more common in women, with only 20% having a higher prevalence in men. There are also sex and gender differences in acute pain sensitivity. Pain is a subjective experience made up of sensory, cognitive, and emotional components. Consequently, there are multiple dimensions through which sex and gender can influence the pain experience. Historically, most preclinical pain research was conducted exclusively in male animals. However, recent studies that included females have revealed significant sex differences in the physiological mechanisms underlying pain, including sex specific involvement of different genes and proteins as well as distinct interactions between hormones and the immune system that influence the transmission of pain signals. Human neuroimaging has revealed sex and gender differences in the neural circuitry associated with pain, including sex specific brain alterations in chronic pain conditions. Clinical pain research suggests that gender can affect how an individual contextualizes and copes with pain. Gender may also influence the susceptibility to develop chronic pain. Sex and gender biases can impact how pain is perceived and treated clinically. Furthermore, the efficacy and side effects associated with different pain treatments can vary according to sex and gender. Therefore, preclinical and clinical research must include sex and gender analyses to understand basic mechanisms of pain and its relief, and to develop personalized pain treatment.

Clinical identification of the stimulus intensity to measure temporal summation of second pain

Temporal summation of second pain (TSSP) has been suggested as a psychophysical index for central sensitization, one of the critical mechanisms in the chronification of pain. However, there is no gold standard for protocols to measure TSSP. The purpose was to establish the stimulus intensity for measuring TSSP. Female patients with chronic myofascial temporomandibular disorders pain (n = 16) and healthy female volunteers with no pain (n = 15) participated. Pain thresholds (PT °C) were measured, and repetitive heat stimuli at three stimulus intensities (PT °C, PT + 1 °C, PT + 2 °C) were applied. TSSP parameters were quantified as TSSP magnitude (TSm) and TSSP frequency (TSf). In healthy female volunteers, pain ratings significantly decreased at PT °C (p < 0.050), besides TSm and TSf at PT + 2 °C were significantly higher than those at PT °C (p < 0.025). In chronic pain patients, pain ratings significantly increased at PT + 1 °C and PT + 2 °C (p < 0.050). At PT + 2 °C, TSm and TSf in chronic pain patients were significantly higher than those in healthy volunteers (p < 0.050). It could be helpful to measure TSSP with the stimulus intensity adjusted individually to the patient’s pain thresholds + 2 °C for assessing central sensitization.