The role of excess subcutaneous fat in pain and sensory sensitivity in obesity

Effect of Transcutaneous Auricular Vagus Nerve Stimulation on Conditioned Pain Modulation in Trigeminal Neuralgia Patients

INTRODUCTION

Conditioned pain modulation (CPM) is a quantitative estimation of the capacity for endogenous pain modulation. Reduced CPM enables chronic painful event development or exacerbates pre-existing pain symptoms. Emerging reports indicate that patients with trigeminal neuralgia (TN) have dysregulated endogenous pain modulation. Transauricular vagus nerve stimulation (taVNS) is known to alleviate both acute and chronic pain symptoms. Its role in modulation or management of TN remains unknown. Here, we evaluated the taVNS efficacy in modulating CPM among TN patients. Conclusions from this investigation may facilitate establishment of novel non-invasive adjunctive approaches to treating TN patients.

METHODS

All research work was conducted at the First Affiliated Hospital of the University of Science and Technology of China (Anhui Provincial Hospital). In all, we recruited 62 study participants, 31 TN patients and 31 healthy volunteers, for a 2-day experimental test. At the beginning of the experiment (Day 1), all subjects received 30 min of active taVNS. On Day 2, they received sham taVNS with the same duration and intensity. Meanwhile, technicians documented participant pressure pain thresholds (PPT) and CPM values at baseline, and at 15 and 30 min post-active or sham taVNS.

RESULTS

A 30-min active taVNS exposure substantially elevated the PPT and CPM effect (P < 0.05) among TN patients, and we also observed a notable rise in the PPT and CPM effect (P < 0.05) among healthy controls. Additionally, there were no serious adverse events from the administered treatment.

CONCLUSION

Exposure to 30 min of active taVNS strongly augmented the CPM effect and elevated the PPT among TN patients and healthy controls. These effects were not observed with sham stimulation. Despite the limitations inherent to survey studies, such as duration and compliance biases, we consider that taVNS is a promising, safe, and cost-effective therapy. In future investigations, we recommend assessment of long-term taVNS application and its effects on CPM and clinical pain.

TRIAL REGISTRATION

ChiCTR2300078673 ( www.Chictr.org.cn ).

Patient Satisfaction and Experience with CT-P17 Following Transition from Reference Adalimumab or Another Adalimumab Biosimilar: Results from the Real-World YU-MATTER Study

BACKGROUND AND OBJECTIVES

Biosimilars are cost-effective alternatives to reference products for patients with inflammatory bowel diseases (IBD) and chronic inflammatory rheumatic diseases (CIRD), but patient beliefs can affect adherence to the transition. This study aimed to explore patient experience and satisfaction after switching to CT-P17, a high-concentration (100 mg/mL), citrate-free adalimumab biosimilar.

PATIENTS AND METHODS

This observational, multicenter, prospective French study included adult patients with IBD or CIRD who switched to CT-P17 from reference adalimumab (R-ADA; 100 mg/mL) or a low-concentration adalimumab biosimilar (ADA-BioS; 50 mg/mL). Patients completed online questionnaires to assess treatment perceptions, satisfaction, and tolerance at study inclusion (under previous treatment) and over 3 months of CT-P17 treatment. The primary criterion was overall patient satisfaction, which was assessed with the question, "What is your global satisfaction with the CT-P17 injection?", using a 7-point Likert scale. Multivariate logistic regression analysis was performed to identify factors associated with increased treatment satisfaction after switching to CT-P17.

RESULTS

The total analysis population included 232 patients (IBD 72.0%, CIRD 28.0%). Median patient age was 57.0 years (interquartile range [IQR] 46.0-63.0), 50.4% were men, and median disease duration was 9 years (IQR 5-16). Approximately half of the cohort (51.2%) switched to CT-P17 from an ADA-BioS (including 19.4% from an ADA-BioS with citrate) and half (48.7%) from R-ADA. The proportion of patients who were satisfied with treatment was stable between baseline (under previous treatment) and 3 months (under CT-P17). More patients reported increased satisfaction after switching to CT-P17 from an ADA-BioS (22.7% vs 8.0% when switching from R-ADA; p = 0.002), or from an ADA-BioS containing citrate (28.9% vs 12.3% when switching from a citrate-free ADA-BioS; p = 0.008). Independent prognostic factors for increased satisfaction were previous treatment with an ADA-BioS (odds ratio [OR] 2.88 [95% confidence interval 1.17-7.08]; p = 0.021) and pain at the injection site under previous treatment (OR 1.26 [1.08-1.47]; p = 0.004). Significantly fewer patients reported pain, redness, itching, and hematoma after 3 months of CT-P17 treatment versus baseline (p < 0.001).

CONCLUSIONS

The majority of patients had stable or increased treatment satisfaction after switching from R-ADA or an ADA-BioS to CT-P17. In particular, switching to CT-P17 from a low-concentration ADA-BioS or an ADA-BioS containing citrate was associated with increased patient satisfaction. An improvement in overall tolerance with CT-P17 versus previous adalimumab treatment was also reported.

TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT05427942, registered June 22, 2022.

Pressure and cold pain threshold reference values in a pain-free older adult population

Background

More sex-specific pain sensitivity normative values from population-based cohorts in pain-free older adults are required. The aims of this study were (1) to provide sex- and age-specific normative values of pressure and cold pain thresholds in older pain-free adults and (2) to examine the association of potential correlates of pain sensitivity with pain threshold values.

Methods

This study investigated sex-specific pressure (lumbar spine, tibialis anterior, neck and dorsal wrist) and cold (dorsal wrist) pain threshold estimates for older pain-free adults aged 41-70 years. This cross-sectional study used participants (n = 212) from the Raine Study Gen1-26 year follow-up. The association of pain thresholds, with correlates including sex, test site, ethnicity, waist-hip ratio, smoking status, health-related quality of life, depression, anxiety and stress symptoms, sleep quality, socioeconomic status and physical activity levels, was examined.

Results

Values for pressure and cold pain thresholds for older pain-free adults are provided, grouped by vicennium, sex and test site (pressure). Statistically significant independent correlates of increased pressure pain sensitivity were test site, ethnicity and sex. Only lower waist/hip ratio was a statistically significant, independent correlate of increased cold pain sensitivity.

Conclusions

This study provides robust sex- and age-specific normative values for pressure pain threshold and cold pain threshold for an older adult pain-free population. Combined with existing values, these data provide an important resource in assisting interpretation of pain sensitivity in clinical pain disorders and provide insights into the complex association of pain sensitivity with correlates that can be used in research.

Towards more tolerable subcutaneous administration: Review of contributing factors for improving combination product design

Subcutaneous (SC) injections can be associated with local pain and discomfort that is subjective and may affect treatment adherence and overall patient experience. With innovations increasingly focused on finding ways to deliver higher doses and volumes (≥2 mL), there is a need to better understand the multiple intertwined factors that influence pain upon SC injection. As a priority for the SC Drug Development & Delivery Consortium, this manuscript provides a comprehensive review of known attributes from published literature that contribute to pain/discomfort upon SC injection from three perspectives: (1) device and delivery factors that cause physical pain, (2) formulation factors that trigger pain responses, and (3) human factors impacting pain perception. Leveraging the Consortium's collective expertise, we provide an assessment of the comparative and interdependent factors likely to impact SC injection pain. In addition, we offer expert insights and future perspectives to fill identified gaps in knowledge to help advance the development of patient-centric and well tolerated high-dose/high-volume SC drug delivery solutions.

Obesity Is Associated with Altered Rectal Sensitivity in Chronic Constipation

BACKGROUND

Defecation dysfunction may contribute to chronic constipation (CC), but the impact of obesity on anorectal physiology in CC remains unclear. We aimed to evaluate the relationship between obesity and anorectal function on physiologic testing in patients presenting with CC.

METHODS

This was a retrospective cohort study of consecutive adults who underwent high resolution anorectal manometry (HRAM) at a tertiary center for CC. Patient demographics, clinical history, surgical/obstetric history, medications, and HRAM results were reviewed. Patients were classified into obese (BMI > 30 kg/m2) vs non-obese (BMI < 30 kg/m2) groups at the time of HRAM. Fisher-exact/student t-test for univariate analyses and general linear regression for multivariable analysis were performed.

RESULTS

383 adults (mean 50.3 years; 85.8% female) with CC were included. On HRAM, patients with obesity had lower anal sphincter resting tone (37.3 vs 48.5 mmHg, p = 0.005) and maximum squeeze pressure (104.8 mmHg vs 120.0 mmHg, p = 0.043). No significant differences in dyssynergia (61% vs 53%, p = 0.294) and failed balloon expulsion (18% vs 25%, p = 0.381) were found between obese and non-obese groups. On balloon distention testing, the maximum tolerated (163.5 vs 147.6 mL, p = 0.042) and urge sensation (113.9 vs 103.7 mL, p = 0.048) volumes were significantly increased among patients with obesity. After adjusting for potential confounders, obesity remained independently associated with increased maximum tolerated volume (β-coefficient 13.7, p = 0.049).

CONCLUSION

Obesity was independently associated with altered rectal sensitivity among patients with CC. Altered rectal sensation may play an important role in CC among patients with obesity. Anorectal physiology testing should be considered to understand the pathophysiology and guide management.

Development and validation of machine learning based prediction model for postoperative pain risk after extraction of impacted mandibular third molars

Background

Predicting postoperative pain risk in patients with impacted mandibular third molar extractions is helpful in guiding clinical decision-making, enhancing perioperative pain management, and improving the patients' medical experience. This study aims to develop a prediction model based on machine learning algorithms to identify patients at high risk of postoperative pain after tooth extraction.

Methods

We conducted a prospective cohort study. Outpatients with impacted mandibular third molars were recruited and the outcome was defined as the NRS (Numerical Rating Scale) score of peak postoperative pain within 24 h after the operation ≥7, which is considered a high risk of postoperative pain. We compared the models built using nine different machine learning algorithms and conducted internal and time-series external validations to evaluate the model's predictive performances in terms of the area under the curve (AUC), accuracy, sensitivity, specificity, and F1-value.

Results

A total of 185 patients and 202 cases of impacted mandibular third molar data were included in this study. Five modeling variables were screened out using least absolute selection and shrinkage operator regression, including physician qualification, patient self-reported maximum pain sensitivity, OHI-S-CI, BMI, and systolic blood pressure. The overall performance of the random forest model was evaluated. The AUC, sensitivity, and specificity of the prediction model built using the random forest method were 0.879 (0.861-0.891), 0.857, and 0.846, respectively, for the training set and 0.724 (0.673-0.732), 0.667, and 0.600, respectively, for the time series validation set.

Conclusions

This study developed a machine learning-based postoperative pain risk prediction model for impacted mandibular third molar extraction, which is promising for providing a theoretical basis for better pain management to reduce postoperative pain after third molar extraction.

The PATIENT Approach: A New Bundle for the Management of Chronic Pain

BACKGROUND

Chronic pain is one of the most challenging diseases for physicians as its etiology and manifestations can be extremely varied. Many guidelines have been published and many therapeutic options are nowadays available for the different types of pain. Given the enormous amount of information that healthcare providers must handle, it is not always simple to keep in mind all the phases and strategies to manage pain. We here present the acronym PATIENT (P: patient's perception; A: assessment; T: tailored approach; I: iterative evaluation; E: education; N: non-pharmacological approach; T: team), a bundle which can help to summarize all the steps to follow in the management of chronic pain.

METHODS

We performed a PubMed search with a list of terms specific for every issue of the bundle; only English articles were considered.

RESULTS

We analyzed the literature investigating these topics to provide an overview of the available data on each bundle's issue; their synthesis lead to an algorithm which may allow healthcare providers to undertake every step of a patient's evaluation and management.

DISCUSSION

Pain management is very complex; our PATIENT bundle could be a guide to clinicians to optimize a patient's evaluation and treatment.

Facilitated Central Pain Mechanisms Across the Menstrual Cycle in Dysmenorrhea and Enlarged Pain Distribution in Women With Longer Pain History

Dysmenorrhea (DYS), or recurrent menstrual pain, is a highly prevalent pain condition among otherwise healthy women. However, the progression of DYS over time and the influence of the menstrual cycle phases need to be better understood. While the location and distribution of pain have been used to assess pain mechanisms in other conditions, they are unexplored in DYS. Thirty otherwise healthy women with severe DYS and 30 healthy control women were recruited into 3 subgroups (n = 10) according to the length of their menstrual history (<5, 5-15, or>15 years since menarche). The intensity and distribution of menstrual pain were recorded. Pressure pain thresholds at abdominal, hip, and arm sites, pressure-induced pain distribution, temporal summation of pain, and pain intensity after pressure cessation over the gluteus medius were assessed at 3 menstrual cycle phases. Compared with the healthy control women, those with DYS showed lower pressure pain thresholds in every site and menstrual cycle phase (P < .05), enlarged pressure-induced pain areas during menstruations (P < .01), and increased temporal summation and pain intensity after pressure cessation in the overall menstrual cycle (P < .05). Additionally, these manifestations were enhanced during the menstrual and premenstrual phases compared to ovulation in women with DYS (P < .01). Women with long-term DYS demonstrated enlarged pressure-induced pain distribution, enlarged menstrual pain areas, and more days with severe menstrual pain compared to the short-term DYS subgroup (P < .01). Pressure-induced and menstrual pain distributions were strongly correlated (P < .001). These findings suggest that severe DYS is a progressive condition underscored by facilitated central pain mechanisms associated with pain recurrence and exacerbation. PERSPECTIVE: Enlarged pressure-induced pain areas occur in DYS, associated with the length of the condition and the distribution of menstrual pain. Generalized hyperalgesia is present throughout the entire menstrual cycle and intensifies during premenstrual and menstrual phases.

Cutaneous warmth and hotness thresholds to radiation heat exposure at a distance of 10 cm from 17 body regions

The purpose of the present study was to evaluate body regional differences in cutaneous warmth and hotness thresholds in relation to radiant heat exposure. Fourteen male subjects participated in this study (age: 25 ± 5 y, height: 176.6 ± 5.5 cm, body weight: 70 ± 5.8 kg). Cutaneous warmth and hotness thresholds were measured on the forehead, neck, chest, abdomen, upper back, lower back, upper arm, forearm, palm, back of hand, front thigh, shin, top of foot, buttock, back thigh, calf, and sole. The forehead (34.8 ± 0.2 °C), lower back (34.1 ± 1.2 °C) and palm (34.3 ± 0.7 °C) had the highest warmth thresholds, whereas the foot (29.8 ± 1.9 °C) and sole (28.0 ± 2.1 °C) had the lowest values among the 17 regions (P<0.001). Higher warmth thresholds were related to higher initial skin temperatures (Tsk) (r=0.972, P<0.001). Increases in Tsk for detecting warmth sensation were smaller for the lower back with a rise of 0.2 ± 0.4 °C and the abdomen (0.3 ± 0.3 °C) than for the buttock (0.9 ± 0.8 °C) and sole (0.8 ± 0.6 °C) (P<0.05). Increases in Tsk for detecting hotness sensation ranged from 0.5 to 1.5 °C. Warmth and hotness thresholds on the abdomen or sole had significant relationships with body mass index, indicating that the overweight are less sensitive to detecting radiant heat on the abdomen or sole. Thermal thresholds from radiant heat exposure of 100 cm2 were lower than the values from conductive heat exposure of 6.25 cm2, which might be explained by the effect of spatial summation.

Spatial summation of thermal sensitivity is limited to small areas: Comparisons of the forehead, forearm, abdomen, and foot

The purpose of the present study was to examine if spatial summation in thermal sensitivity exists when stimulating areas larger than about 1% of body surface area (BSA) (approximately 200 cm2). We hypothesized that spatial summation would exist within a limited area and the effect would be insignificant for over the 1%BSA. Fifteen young males participated in this study and we measured their warmth and hot sensation thresholds on the four body regions (the forehead, forearm, abdomen, and instep) using the three sizes of radiant film heaters (10 × 10, 15 × 15, and 20 × 20 cm2 heating film area). The heating panel was kept at a distance of 10 cm from the skin and the surface temperature of the heating panel increased by 1 °C·s-1. The results showed that warmth and hot sensation thresholds were higher for the 100 cm2 condition than the 225 or 400 cm2 conditions (P < 0.05), but no differences were found between the 225 and 400 cm2 conditions. Secondly, the instep was most insensitive to the gradual increase of radiant heat among the four body regions for all three stimulating film sizes, even though the hot threshold was lowest for the instep because the initial foot temperature was lower than other skin temperatures. In summary, spatial summation in thermal sensitivity was found for the 100 and 225 cm 2 conditions, but not for the 225 and 400 cm2 conditions. These results suggest that spatial summation exists but limited to small stimulating areas, smaller than approximately 1% BSA.

The biopsychosocial impacts of anxiety on overactive bladder in women

AIMS

Links between emotional state and the bladder have long been recognized, as psychological comorbidity is a common feature of overactive bladder (OAB). However, how psychological factors might contribute to the development and severity of OAB remains unclear. Therefore, we sought to examine the effect of anxiety on OAB with a specific focus on bladder hypersensitivity.

METHODS

In a sample of 120 adult women with OAB, we compared those with at least mild anxiety (PROMIS Anxiety score ≥55) to those with lower anxiety. Analyses focused on patient-reported questionnaires assessing urinary symptom severity and quality of life, psychological stress symptoms, general somatic symptoms, and results of quantitative sensory testing (QST), including temporal summation to heat pain (TSP). TSP was used to index elevated C-fiber responsiveness (i.e., central sensitization).

RESULTS

Thirty-six (30%) women had at least mild anxiety. While there were no group differences for urinary symptom severity, more anxious women reported worse OAB-specific quality of life, greater psychological stress burden, higher stress reactivity, and greater somatic symptoms. On QST, there were no differences between anxiety groups for pain threshold (43.6 ± 3.1°C vs. 44.0 ± 3.1°C, p = 0.6) and tolerance (47.3 ± 1.5°C vs. 47.4 ± 1.6°C, p = 0.7). However, those with anxiety had significantly higher TSP than those without anxiety (6.0 ± 4.8 vs. 3.7 ± 3.9, p = 0.006), indicating greater central sensitization.

CONCLUSIONS

Women with OAB and at least mild anxiety symptoms reported greater psychosocial burdens (i.e., psychological stress, stress reactivity, OAB-specific QOL) and somatic symptom severity and demonstrated greater central sensitization on QST than those without anxiety. These findings support the hypothesis that anxiety and psychological stress impact hypersensitivity mechanisms that may underlie and contribute to OAB, although further research is needed to better understand how and to what extent.

Dense 3D pressure discomfort threshold (PDT) map of the human head, face and neck: A new method for mapping human sensitivity

When designing wearables that interface with the human head, face and neck, designers and engineers consider human senses, ergonomics and comfort. A dense 3D pressure discomfort threshold map could be helpful, but does not exist yet. Differences in pressure discomfort threshold for areas of the head, neck and face were recorded, to create a 3D pressure discomfort threshold map. Between 126 and 146 landmarks were placed on the left side of the head, face and neck of twenty-eight healthy participants (gender balanced). The positions of the landmarks were specified using an EEG 10-20 system-based landmark-grid on the head and a self-developed grid on the face and neck. A 3D scan was made to capture the head geometry and landmark coordinates. In a randomised order, pressure was applied on each landmark with a force gauge until the participant indicated experiencing discomfort. By interpolating all collected pressure discomfort thresholds based on their corresponding 3D coordinates, a dense 3D pressure discomfort threshold map was made. A relatively low-pressure discomfort threshold was found in areas around the nose, neck front, mouth, chin-jaw, cheek and cheekbone, possibly due to the proximate or direct location of nerves, blood veins and soft (muscular) tissue. Medium pressure discomfort was found in the neck back, forehead and temple regions. High pressure discomfort threshold was found in the back of the head and scalp, where skin is relatively thin and closely supported by bone, making these regions interesting for mounting or resting head, face and neck related equipment upon.

Effects of inactivated SARS-CoV-2 vaccination on male fertility: A retrospective cohort study

Numerous studies have revealed severe damage to male fertility from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, raising concerns about the potential adverse impact on reproductive function of the coronavirus disease 2019 (COVID-19) vaccine developed based on the virus. Interestingly, there are several researchers who have studied the impact of the COVID-19 mRNA vaccine since then but have come up with conflicting results. As a near-ideal candidate for mass immunization programs, inactivated SARS-CoV-2 vaccine has been widely used in many countries, particularly in less wealthy nations. However, little is known about its effect on male fertility. Here, we conducted a retrospective cohort study at a single large center for reproductive medicine in China between December 2021 and August 2022. Five hundred and nineteen fertile men with no history of laboratory-confirmed COVID-19 were included and categorized into four groups based on their vaccination status: unvaccinated group (n = 168), one-dose vaccinated group (n = 8), fully vaccinated group (n = 183), and booster group (n = 160). All of them underwent a semen analysis and most had serum sex hormone levels tested. There were no significant differences in all semen parameters and sex hormone levels between the unvaccinated group and either vaccinated group. To account for possible vaccination-to-test interval-specific changes, sub-analyses were performed for two interval groups: ≤90 and >90 days. As expected, most of the semen parameters and sex hormone levels remained unchanged between the control and vaccinated groups. However, participants in vaccinated group (≤90 days) have decreased total sperm motility and increased follicle-stimulating hormone level compared with the ones in unvaccinated group. Moreover, some trends similar to those found during COVID-19 infection and recovery were observed in our study. Fortunately, all values are within the normal range. In addition, vaccinated participants reported few adverse reactions. No special medical intervention was required, and no serious adverse reactions happened. Our study suggests that inactivated SARS-CoV-2 vaccination does not impair male fertility, possibly due to the low frequency of adverse effects. This information reassures young male population who got this vaccine worldwide, and helps guide future vaccination efforts.

Lean Mass is Associated with, but Does Not Mediate Sex Differences in Pressure Pain Sensitivity in Healthy Adults

Background

Sex differences exist in pain sensitivity, however, the underlying mechanism(s) that explain these differences are not fully understood. Pain sensitivity has been shown to be influenced by body mass index, but limited data exist on the role of body composition on pain sensitivity. The purpose was to examine the influence of body composition on pain sensitivity in males and females.

Methods

This cross-sectional study design used pressure pain thresholds (PPT) of 87 participants (45 female) who were assessed in the vastus lateralis (leg PPT) and brachioradialis (arm PPT) using a pressure algometer. Fat and lean tissue were assessed via dual-energy X-ray absorptiometry (DXA). A two group by two limb, repeated measured ANOVA was used to assess differences between limbs and sex. Spearman correlations and hierarchical regression analyses were employed to determine the association between body composition and PPT.

Results

Males had higher PPTs then females (P<0.05) and had higher DXA assessed lean and lower levels fat mass (P<0.05). Total body and limb specific lean mass was associated with PPTs (r≥0.34; P<0.05). Hierarchical regression analysis revealed lean mass was a significant predictor of 8% of the variance in arm PPT (P<0.006) and 18% of the variance in leg PPT (P<0.001). However, lean mass was not found to statistically mediate the observed sex differences in PPT.

Conclusion

This finding suggests lean mass may play a previously unknown role in sex differences in pressure pain sensitivity. Future studies are needed to confirm this finding and a larger sample size is likely required to have sufficient power to perform the mediation analysis.

To Calibrate or not to Calibrate? A Methodological Dilemma in Experimental Pain Research

To calibrate or not to calibrate? This question is raised by almost everyone designing an experimental pain study with supra-threshold stimulation. The dilemma is whether to individualize stimulus intensity to the pain threshold / supra-threshold pain level of each participant or whether to provide the noxious stimulus at a fixed intensity so that everyone receives the identical input. Each approach has unique pros and cons which need to be considered to i) accurately design an experiment, ii) enhance statistical inference in the given data and, iii) reduce bias and the influence of confounding factors in the individual study e.g., body composition, differences in energy absorption and previous experience. Individualization requires calibration, a procedure already irritating the nociceptive system but allowing to match the pain level across individuals. It leads to a higher variability of the stimulus intensity, thereby influencing the encoding of "noxiousness" by the central nervous system. Results might be less influenced by statistical phenomena such as ceiling/floor effects and the approach does not seem to rise ethical concerns. On the other hand, applying a fixed (standardized) intensity reduces the problem of intensity encoding leading to a large between-subjects variability in pain responses. Fixed stimulation intensities do not require pre-exposure. It can be proposed that one method is not preferable over another, however the choice depends on the study aim and the desired level of external validity. This paper discusses considerations for choosing the optimal approach for experimental pain studies and provides recommendations for different study designs. PERSPECTIVE: To calibrate pain or not? This dilemma is related to almost every experimental pain research. The decision is a trade-off between statistical power and greater control of stimulus encoding. The article decomposes both approaches and presents the pros and cons of either approach supported by data and simulation experiment.

Body fat and skeletal muscle mass, but not body mass index, are associated with pressure hyperalgesia in young adults with patellofemoral pain

BACKGROUND

Young adults with patellofemoral pain (PFP) have a high prevalence of being overweight or obese, which is associated with impaired lower limb function and muscle weakness. However, the impact of being overweight or obese on pain sensitivity has not been explored.

OBJECTIVES

We investigated the association between body fat, skeletal muscle mass, and body mass index (BMI) with pressure hyperalgesia and self-reported pain in young adults with PFP.

METHODS

114 adults with PFP (24 ± 5 years old, 62% women) were recruited. Demographics and self-reported pain (current and worst knee pain intensity in the previous month - 0-100 mm visual analog scale) were recorded. Body fat and skeletal muscle mass were measured using bioelectrical impedance. Pressure hyperalgesia was measured using a handheld algometer (pressure pain threshold) at three sites: center of patella of the painful knee, ipsilateral tibialis anterior, and contralateral upper limb. The association between body fat, skeletal muscle mass, and BMI with pressure hyperalgesia and self-reported pain were investigated using partial correlations and hierarchical regression models (adjusted for sex, bilateral pain, and symptoms duration).

RESULTS

Higher body fat and lower skeletal muscle mass were associated with local, spread, and widespread pressure hyperalgesia (ΔR²=0.09 to 0.17, p ≤ 0.001; ΔR²=0.14 to 0.26, p<0.001, respectively), and higher current self-reported pain (ΔR²=0.10, p<0.001; ΔR²=0.06, p = 0.007, respectively). Higher BMI was associated with higher current self-reported pain (ΔR²=0.10, p = 0.001), but not with any measures of pressure hyperalgesia (p>0.05).

CONCLUSION

Higher body fat and lower skeletal muscle mass help to explain local, spread, and widespread pressure hyperalgesia, and self-reported pain in people with PFP. BMI only helps to explain self-reported pain. These factors should be considered when assessing people with PFP and developing their management plan, but caution should be taken as the strength of association was generally low.

Vapocoolant Spray for Pain Control in Intramuscular Injection Applications: A Prospective, Randomized Controlled Trial

Background Many pharmacological and nonpharmacological methods have been investigated along with advances in pain treatment. One of these nonpharmacological methods is the use of vapocoolant spray.

Objective This study aimedto demonstrate the effectiveness of vapocoolant spray to reduce pain during intramuscular (IM) injection.

Patients and Methods The study included ≥18 years old patients admitted to the emergency department who were asked to undergo IM injection. Patients were randomly divided into two groups as vapocoolant spray and control group. Demographic data, injection side, and visual analog scale (VAS) of the patients were recorded.

Results Mean VAS values during IM injection were significantly lower in patients treated with vapocoolant spray compared with the control group. The severity of pain during IM injection was lower in the vapocoolant spray group as both moderate pain (VAS > 3 cm) and severe pain (VAS > 5.4 cm) compared with the control group.

Conclusion Vapocoolant spray to be applied before IM injection is effective in reducing pain caused by the injection.

Integrating genomics and transcriptomics to identify candidate genes for subcutaneous fat deposition in beef cattle

Fat deposition is a complex economic trait regulated by polygenic genetic basis and environmental factors. Therefore, integrating multi-omics data to uncover its internal regulatory mechanism has attracted extensive attention. Here, we performed genomics and transcriptomics analysis to detect candidates affecting subcutaneous fat (SCF) deposition in beef cattle. The association of 770K SNPs with the backfat thickness captured nine significant SNPs within or near 11 genes. Additionally, 13 overlapping genes regarding fat deposition were determined via the analysis of differentially expressed genes and weighted gene co-expression network analysis (WGCNA). We then calculated the correlations of these genes with BFT and constructed their interaction network. Finally, seven biomarkers including ACACA, SCD, FASN, ACOX1, ELOVL5, HACD2, and HSD17B12 were screened. Notably, ACACA, identified by the integration of genomics and transcriptomics, was more likely to exert profound effects on SCF deposition. These findings provided novel insights into the regulation mechanism underlying bovine fat accumulation.

Personal influencing factors for pressure pain threshold in healthy people: A systematic review and meta-analysis

All studies that investigated personal factors influencing pressure pain threshold (PPT) in healthy people were synthesized. Data was summarized, and risk of bias (RoB) and level of evidence were determined. Results were pooled per influencing factor, grouped by body region and included in meta-analyses. Fifty-four studies were eligible. Five had low, nine moderate, and 40 high RoB. Following meta-analyses, a strong conclusion was found for the influence of scapular position, a moderate for the influence of gender, and a weak for the influence of age (shoulder/arm region) and blood pressure on PPT. In addition, body mass index, gender (leg region), alcohol consumption and pain vigilance may not influence PPT. Based on qualitative summary, depression and menopause may not influence PPT. For other variables there was only preliminary or conflicting evidence. However, caution is advised, since the majority of included studies showed a high RoB and several were not eligible to include in meta-analyses. Heterogeneity was high in the performed meta-analyses, and most conclusions were weak. More standardized research is necessary.

Associations of Body Mass Index With Pain and the Mediating Role of Inflammatory Biomarkers in People With Hand Osteoarthritis

OBJECTIVE

To examine the association of body mass index (BMI) with pain in people with hand osteoarthritis (OA), and explore whether this association, if causal, is mediated by systemic inflammatory biomarkers.

METHODS

In 281 Nor-Hand study participants, we estimated associations between BMI and hand pain, as measured by the Australian/Canadian Osteoarthritis Hand Index (AUSCAN; range 0-20) and Numerical Rating Scale (NRS; range 0-10); foot pain, as measured by NRS (range 0-10); knee/hip pain, as measured by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC; range 0-20); painful total body joint count; and pain sensitization. We fit natural-effects models to estimate natural direct and natural indirect effects of BMI on pain through inflammatory biomarkers.

RESULTS

Each 5-unit increase in BMI was associated with more severe hand pain (on average increased AUSCAN by 0.64 [95% confidence interval (95% CI) 0.23, 1.08]), foot pain (on average increased NRS by 0.65 [95% CI 0.36, 0.92]), knee/hip pain (on average increased WOMAC by 1.31 [95% CI 0.87, 1.73]), generalized pain, and pain sensitization. Mediation analyses suggested that the effects of BMI on hand pain and painful total body joint count were partially mediated by leptin and high-sensitivity C-reactive protein (hsCRP), respectively. Effect sizes for mediation by leptin were larger for the hands than for the lower extremities, and were statistically significant for the hands only.

CONCLUSION

In people with hand OA, higher BMI is associated with greater pain severity in the hands, feet, and knees/hips. Systemic effects of obesity, measured by leptin, may play a larger mediating role for pain in the hands than in the lower extremities. Low-grade inflammation, measured by hsCRP, may contribute to generalized pain in overweight/obese individuals.

Metabolic Phenotypes—The Game Changer in Quality of Life of Obese Patients?

Background: The present study aimed to investigate the association of obesity phenotypes and quality of life (QoL) scales and their relationship with fat mass (FM) parameters. Methods: This study categorized 104 subjects into 4 obesity phenotypes based on BMI and metabolic syndrome status: metabolically healthy obese (MHO), metabolically unhealthy obese (MUO), metabolically healthy non-obese (MHNO), and metabolically unhealthy non-obese (MUNO). Body composition was measured by dual-energy X-ray absorptiometry (DEXA) and metabolic profile was characterized by blood samples. All subjects completed the SF-36 item Short Form Health Survey Questionnaire. Results: Comparing the four obesity phenotypes, significant results were reported for Bodily Pain between MHNO/MUNO (p = 0.034), for Vitality between MHO/MUO (p = 0.024), and for Mental Component Score between MHO/MUO (p = 0.026) and MUO/MUNO (p = 0.003). A more thorough inside-groups analysis yielded a positive and moderate to high correlation between FM parameters and QoL scales in MHO and MHNO, while a negative and weak to moderate correlation was observed in MUO and MUNO. Conclusion: This study reported an inverse U-shaped relationship between FM and QoL in obesity phenotypes, suggesting that metabolic status is a key factor involved in modulating QoL and therefore challenging the idea of obesity as a main driver of low QoL. We recommend the inclusion of FM percentage in the definition of obesity phenotypes in future research, to better evaluate QoL of obesity phenotypes.

Simple Quantitative Sensory Testing Reveals Paradoxical Co-existence of Hypoesthesia and Hyperalgesia in Diabetes

Background: Diabetic neuropathy is characterized by the paradoxical co-existence of hypo- and hyperalgesia to sensory stimuli. The literature shows consistently sensory differences between healthy and participants with diabetes. We hypothesized that due to differences in pathophysiology, advanced quantitative sensory testing (QST) might reveal sensory discrepancies between type 1 (T1D) and type 2 diabetes (T2D). Furthermore, we investigated whether vibration detection thresholds (VDT) were associated with sensory response.

Method: Fifty-six adults with T1D [43 years (28–58)], 99 adults with T2D [65 years (57–71)], and 122 healthy individuals [51 years (34–64)] were included. VDT, pressure pain detection thresholds (pPDT) and tolerance (pPTT), tonic cold pain (hand-immersion in iced water), and central pain mechanisms (temporal summation and conditioned pain modulation) were tested and compared between T1D and T2D. VDT was categorized into normal (< 18 V), intermediary (18–25 V), or high (> 25 V).

Results: In comparison to healthy, analysis adjusted for age, BMI, and gender revealed hypoalgesia to tibial (pPDT): p = 0.01, hyperalgesia to tonic cold pain: p < 0.01, and diminished temporal summation (arm: p < 0.01; abdomen: p < 0.01). In comparison to participants with T2D, participants with T1D were hypoalgesic to tibial pPDT: p < 0.01 and pPTT: p < 0.01, and lower VDT: p = 0.02. VDT was not associated with QST responses.

Conclusion: Participants with T1D were more hypoalgesic to bone pPDT and pPTT independent of lower VDT, indicating neuronal health toward normalization. Improved understanding of differentiated sensory profiles in T1D and T2D may identify improved clinical endpoints in future trials.

Do Metabolically Healthy People with Obesity Have a Lower Health-Related Quality of Life? A Prospective Cohort Study in Taiwan

The association between metabolically healthy obesity (MHO) and health-related quality of life (HRQOL) has not been thoroughly evaluated. This study enrolled 906 adult participants aged 35–55 years between 2009 and 2010 in Northern Taiwan; 427 participants were followed up after eight years. Normal weight, overweight, and obesity were evaluated via body mass index. Metabolic health was defined as the absence of cardiometabolic diseases and having ≤1 metabolic risk factor. HRQOL was evaluated using the 36-Item Short Form Health Survey (SF-36), Taiwan version. Generalized linear mixed-effects models were used to analyze the repeated, measured data with adjustment for important covariates. Compared with metabolically healthy normal weight individuals, participants with metabolically unhealthy normal weight and obesity had a significantly poorer physical component summary score (β (95% CI) = −2.17 (−3.38–−0.97) and −2.29 (−3.70–−0.87), respectively). There were no significant differences in physical and mental component summary scores among participants with metabolically healthy normal weight, overweight, and obesity. This study showed that metabolically healthy individuals with obesity and normal weight had similar HRQOL in physical and mental component summary scores. Maintaining metabolic health is an ongoing goal for people with obesity.

Pain sensitivity does not differ between obese and healthy weight individuals

Introduction

There is emerging evidence suggesting a relationship between obesity and chronic pain.

Objectives

The aim of this study was to determine whether pain-free obese individuals display altered pain responses to acute noxious stimuli, thus raising the possibility of greater pain sensitivity and potential susceptibility for chronic pain development.

Methods

Psychophysical and anthropometric data were collected from 38 individuals with an obese body mass index (BMI) classification (BMI ≥ 30) and 41 age/sex-matched individuals of a healthy BMI (BMI < 24.9). Because BMI may be an inaccurate index of obesity, additional anthropometric parameters of central adiposity and percent body fat were examined. Pain responses to suprathreshold noxious heat and cold stimuli were examined. Subjects provided pain intensity and unpleasantness ratings to noxious heat (49°C) applied at varying durations and locations (ventral forearm/lower leg). Cold pain ratings, thresholds, and tolerances were obtained after immersion of the hand in a cold-water bath (0-2°C). Between-group differences in pain responses, as well as relationships between pain responses and obesity parameters, were examined. Importantly, confounds that may influence pain such as anxiety, depression, impulsivity, sleepiness, and quality of life were assessed.

Results

No between-group differences in pain sensitivity to noxious heat and cold stimuli were found. No relationships were found between central adiposity or body fat (percentage or distribution) and pain responses to noxious heat or cold stimuli.

Conclusions

Obesity has minimal influence on pain sensitivity. Accordingly, it is unlikely that obesity alone increases susceptibility for chronic pain development through amplification of nociceptive processes.

Obesity and the Receipt of Prescription Pain Medications in the US

BACKGROUND

Little is known about disparities in pain treatment associated with weight status despite prior research on weight-based discrepancies in other realms of healthcare and stigma among clinicians.

OBJECTIVE

To investigate the association between weight status and the receipt of prescription analgesics in a nationally representative sample of adults with back pain, adjusting for the burden of pain.

DESIGN

Cross-sectional analyses using the Medical Expenditure Panel Survey (2010-2017).

PARTICIPANTS

Five thousand seven hundred ninety-one civilian adults age ≥ 18 with back pain.

MAIN MEASURES

We examine the odds of receiving prescription analgesics for back pain by weight status using logistic regression. We study the odds of receiving (1) any pain prescription, (2) three pain prescription categories (opioid only, non-opioid only, the combination of both), and (3) opioids conditional on having a pain prescription.

KEY RESULTS

The odds of receiving pain prescriptions increase monotonically across weight categories, when going from normal weight to obesity II/III, despite adjustments for the burden of pain. Relative to normal weight, higher odds of receiving any pain prescription is associated with obesity I (OR = 1.30 [95% CI = 1.04-1.63]) and obesity II/III (OR = 1.72 [95% CI = 1.36-2.18]). Obesity II/III is also associated with higher odds of receiving opioids only (OR = 1.53 [95% CI = 1.16-2.02]), non-opioids only (OR = 1.77 [95% CI = 1.21-2.60]), and a combination of both (OR = 2.48 [95% CI = 1.44-4.29]). Obesity I is associated with increased receipt of non-opioids only (OR = 1.55 [95% CI = 1.07-2.23]). Conditional on having a pain prescription, the odds of receiving opioids are comparable across weight categories.

CONCLUSIONS

This study suggests that, relative to those with normal weight, adults with obesity are more likely to receive prescription analgesics for back pain, despite adjustments of the burden of pain. Hence, the possibility of weight-based undertreatment is not supported. These findings are reassuring because individuals with obesity generally experience a higher prevalence of back pain. The possibility of over-treatment associated with obesity, however, may warrant further investigation.

When one suffers less, all suffer less: Individual pain ratings are more effective than group ratings in producing placebo hypoalgesia

Background

Placebo hypoalgesia can be induced by observing a person (model) whose pain relief is the result of the use of an inert substance or procedure. This study examined whether verbal modelling, that is, showing pain ratings provided by other people, is sufficient to induce placebo hypoalgesia.

Methods

Participants from the experimental groups were acquainted with pain ratings (presented on VASs) derived from a single person (groups 1 and 3) or a group of people (groups 2 and 4) that were allegedly subjected to the same painful procedure. The ratings of pain stimuli that were allegedly applied with placebo were lower than the ratings of stimuli applied without placebo. In two of the experimental groups (group 3 and 4), participants also watched a video recording showing individuals who allegedly provided pain ratings; however, they did not observe them undergoing pain stimulation. The control group did not undergo any manipulation. Then, the participants received a series of the same thermal pain stimuli that were applied either with or without placebo and rated their intensity.

Results

Placebo hypoalgesia was induced only in participants presented with pain ratings provided by a single person, regardless of whether this person was previously seen. However, the pain ratings presented to the participants generally decreased individual pain sensations, regardless of whether they came from a group of people or a single person.

Conclusions

Verbal modelling can produce placebo hypoalgesia and reduce pain sensations. It may be effectively used in clinical practice to modify patients' responses to pain treatment.

Significance

This study shows that knowledge about pain ratings provided by another person is sufficient to induce placebo hypoalgesia; thus, neither direct nor indirect observation of a person experiencing pain is necessary to induce this effect. Pain ratings derived from a group of people can decrease pain sensations but they do not produce placebo hypoalgesia.

Sources of Individual Differences in Pain

Pain is an immense clinical and societal challenge, and the key to understanding and treating it is variability. Robust interindividual differences are consistently observed in pain sensitivity, susceptibility to developing painful disorders, and response to analgesic manipulations. This review examines the causes of this variability, including both organismic and environmental sources. Chronic pain development is a textbook example of a gene-environment interaction, requiring both chance initiating events (e.g., trauma, infection) and more immutable risk factors. The focus is on genetic factors, since twin studies have determined that a plurality of the variance likely derives from inherited genetic variants, but sex, age, ethnicity, personality variables, and environmental factors are also considered.

Reduction in Pain Inhibitory Modulation and Cognitive-Behavioral Changes in Patients With Chronic Low Back Pain: A Case-Control Study

BACKGROUND

Recent studies indicate that the assessment of conditioned pain modulation (CPM) responses and emotional factors can provide important information regarding chronification mechanisms, choices for more efficient therapeutic strategies, and clinical variables supporting a therapeutic prognosis.

AIMS

To investigate the impact of nonspecific chronic low back pain (NSCLBP) on CPM and psychosocial factors in individuals with NSCLBP compared with healthy controls.

DESIGN

Case-control study.

METHODS

Eighteen patients with NSCLBP and 18 healthy controls were recruited for this study. Pain intensity and affective-emotional aspects of pain, functional disability, kinesiophobia, depression, anxiety, and catastrophizing pain were obtained using a questionnaire. A CPM protocol was established to assess the functioning of the descending inhibitory system, with a cold pressor test as a conditioning stimulus and pressure pain threshold as a test stimulus. The maximal isometric strength of the trunk extensors also was evaluated.

RESULTS

Healthy participants demonstrated a greater CPM response than those with NSCLBP. Patients with NSCLBP exhibited significantly lower pressure pain threshold than healthy subjects. Moreover, patients with NSCLBP presented with a considerable exacerbation of cognitive-behavioral changes. NSCLBP patients showed diminished maximal isometric strength of the trunk extensor compared to healthy subjects.

CONCLUSIONS

The endogenous pain inhibition system is reduced in patients with NSCLBP, with significant cognitive-behavioral changes indicated by high levels of anxiety and moderate pain intensity.

SETTING

Clinical School of Physical Therapy of the Federal University of Delta of Parnaíba, Piauí - Brazil.

PARTICIPANTS/SUBJECTS

36 subjects with and without NSCLBP.

Alterations in pronociceptive and antinociceptive mechanisms in patients with low back pain: a systematic review with meta-analysis

Altered pronociceptive and antinociceptive mechanisms are often implicated in painful conditions and have been increasingly studied over the past decade. For some painful conditions, alterations are well-established, but in populations with low back pain (LBP), there remains considerable debate whether these mechanisms are altered. The present systematic review aimed to address this issue by identifying studies assessing conditioned pain modulation (CPM) and/or temporal summation of pain (TSP) in patients with LBP, comparing with either a healthy control group or using a method with reference data available. Qualitative synthesis and quantitative meta-analysis of group differences were performed. For CPM and TSP, 20 and 29 original articles were eligible, with data for meta-analysis obtainable from 18 (1500 patients and 505 controls) and 27 (1507 patients and 1127 controls) studies, respectively. Most studies were of poor-to-fair quality with significant heterogeneity in study size, population, assessment methodology, and outcome. Nonetheless, CPM was impaired in patients with LBP compared with controls (standardized mean difference = -0.44 [-0.64 to -0.23], P < 0.001), and the magnitude of this impairment was related to pain chronicity (acute/recurrent vs chronic, P = 0.003), duration (RS = -0.62, P = 0.006), and severity (RS = -0.54, P = 0.02). Temporal summation of pain was facilitated in patients with LBP compared with controls (standardized mean difference = 0.50 [0.29-0.72], P < 0.001), and the magnitude of this facilitation was weakly related to pain severity (RS= 0.41, P = 0.04) and appeared to be influenced by test modality (P < 0.001). Impaired CPM and facilitated TSP were present in patients with LBP compared with controls, although the magnitude of differences was small which may direct future research on the clinical utility.

Using Portable Ultrasound to Monitor the Neuromuscular Reactivity to Low-Frequency Electrical Stimulation

Neuromuscular electrical stimulation (NMES) is useful for muscle strengthening and for motor restoration of stroke patients. Using a portable ultrasound instrument, we developed an M-mode imaging protocol to visualize contractions elicited by NMES in the quadriceps muscle group. To quantify muscle activation, we performed digital image processing based on the Teager–Kaiser energy operator. The proposed method was applied for 35 voluntary patients (18 women and 17 men), of 63.8 ± 14.1 years and body mass index (BMI) 30.2 ± 6.70 kg/m² (mean ± standard deviation). Biphasic, rectangular electric pulses of 350 µs duration were applied at two frequencies (60 Hz and 120 Hz), and ultrasound was used to assess the sensory threshold (ST) and motor threshold (MT) amplitude of the NMES signal. The MT was 23.4 ± 4.94 mA, whereas the MT to ST ratio was 2.69 ± 0.57. Linear regression analysis revealed that MT correlates poorly with body mass index (R² = 0.004) or with the thickness of the subcutaneous adipose tissue layer that covers the treated muscle (R² = 0.013). Our work suggests that ultrasound is suitable to visualize neuromuscular reactivity during electrotherapy. The proposed method can be used in the clinic, enabling the physiotherapist to establish personalized treatment parameters.

Interrelationship of Neurogenic Obesity and Chronic Neuropathic Pain in Persons With Spinal Cord Injury

The prevalence of obesity and of neuropathic pain are both estimated at above 50% in the population of people with chronic spinal cord injury (SCI). These secondary consequences of SCI have significant negative impact on physical functioning, activities of daily living, and quality of life. Investigations of relationships between weight or body composition and chronic neuropathic pain in people with SCI are lacking, but investigations in non-SCI cohorts suggest an association between obesity and the presence and severity of neuropathic pain conditions. In the present article, we present a review of the literature linking obesity and neuropathic pain and summarize findings suggesting that metabolic syndrome and chronic, systemic inflammation due to excess adiposity increase the risk for neuropathic pain after an SCI.

Advances in Screening, Early Diagnosis and Accurate Staging of Diabetic Neuropathy

The incidence of both type 1 and type 2 diabetes is increasing worldwide. Diabetic peripheral neuropathy (DPN) is among the most distressing and costly of all the chronic complications of diabetes and is a cause of significant disability and poor quality of life. This incurs a significant burden on health care costs and society, especially as these young people enter their peak working and earning capacity at the time when diabetes-related complications most often first occur. DPN is often asymptomatic during the early stages; however, once symptoms and overt deficits have developed, it cannot be reversed. Therefore, early diagnosis and timely intervention are essential to prevent the development and progression of diabetic neuropathy. The diagnosis of DPN, the determination of the global prevalence, and incidence rates of DPN remain challenging. The opinions vary about the effectiveness of the expansion of screenings to enable early diagnosis and treatment initiation before disease onset and progression. Although research has evolved over the years, DPN still represents an enormous burden for clinicians and health systems worldwide due to its difficult diagnosis, high costs related to treatment, and the multidisciplinary approach required for effective management. Therefore, there is an unmet need for reliable surrogate biomarkers to monitor the onset and progression of early neuropathic changes in DPN and facilitate drug discovery. In this review paper, the aim was to assess the currently available tests for DPN's sensitivity and performance.

Understanding and Minimising Injection-Site Pain Following Subcutaneous Administration of Biologics: A Narrative Review

Injection-site pain (ISP) is a subjective side effect that is commonly reported with the subcutaneous administration of biological agents, yet it may only be a concern to some. Multiple factors related to the product formulation, such as pH, volume and excipients, and/or to the injection process have the potential to contribute to ISP, while patient-related factors, such as low body weight, gender and age, can make an individual more susceptible to experiencing ISP. While total elimination of ISP remains unlikely with any subcutaneously administered agent, it can be minimised by helping the patient to develop a confident and competent injection technique via robust and effective training. Careful management of patient expectations along with open discussion regarding the potential risk of ISP may serve to minimise treatment-related anxieties and, importantly, allow the patient to remain in control of his/her treatment. Other interventions to help minimise ISP include psychological interventions, allowing biologics to reach room temperature prior to injection, using the most suitable injection device for the individual patient and selecting an alternative drug formulation, when available. Productive patient–physician communication remains important in order to support and optimise treatment experience and adherence, while also providing the opportunity for patients to discuss any ISP-related issues.

Instrumental validity and intra/inter-rater reliability of a novel low-cost digital pressure algometer

Background

Pain assessment is a key measure that accompanies treatments in a wide range of clinical settings. A low-cost valid and reliable pressure algometer would allow objective assessment of pressure pain to assist a variety of health professionals. However, the pressure algometer is often expensive, which limits its daily use in both clinical and research settings.

Objectives

This study aimed to assess the instrumental validity, and the intra- and inter-rater reliability of an inexpensive digital adapted pressure algometer.

Methods

A single rater applied 60 random compressions on a force platform. The pressure pain thresholds of 20 volunteers were collected twice (3 days apart) by two raters. The main outcome measurements were as follows: the maximal peak force (in kPa) and the pressure pain threshold (adapted pressure algometer vs. force platform). Cronbach’s α test was used to assess internal consistency. The standard error of measurement provided estimates of measurement error, and the measurement bias was estimated with the Bland–Altman method, with lower and upper limits of agreement.

Results

No differences were observed when comparing the compression results (P = 0.51). The validity and internal intra-rater consistencies ranged from 0.84 to 0.99, and the standard error of measurement from 0.005 to 0.04 kPa. Very strong (r = 0.73–0.74) to near-perfect (r = 0.99) correlations were found, with a low risk of bias for all measurements. The results demonstrated the validity and intra-rater reliability of the digitally adapted pressure algometer. Inter-rater reliability results were moderate (r = 0.55–0.60; Cronbach’s α = 0.71–0.75).

Conclusion

The adapted pressure algometer provide valid and reliable measurements of pressure pain threshold. The results support more widespread use of the pressure pain threshold method among clinicians.

Quantitative Sensory Testing in Adolescents with Co-occurring Chronic Pain and Obesity: A Pilot Study

Factors such as gender, ethnicity, and age affect pain processing in children and adolescents with chronic pain. Although obesity has been shown to affect pain processing in adults, almost nothing is known about pediatric populations. The aim of this pilot study was to explore whether obesity alters sensory processing in adolescents with chronic pain. Participants were recruited from a chronic pain clinic (Chronic Pain (CP), n = 12 normal weight; Chronic Pain + Obesity (CPO), n = 19 overweight/obesity) and from an obesity clinic (Obesity alone (O), n = 14). The quantitative sensory testing protocol included assessments of thermal and mechanical pain thresholds and perceptual sensitization at two sites with little adiposity. The heat pain threshold at the hand was significantly higher in the CPO group than in either the CP or O groups. Mechanical pain threshold (foot) was significantly higher in the CPO group than the CP group. No differences were found on tests of perceptual sensitization. Correlations between experimental pain and clinical pain parameters were found for the CPO group, but not for the CP group. This preliminary study provides important lessons learned for subsequent, larger-scale studies of sensory processing for youth with co-occurring chronic pain and obesity.

Modulation of Pain Sensitivity by Chronic Consumption of Highly Palatable Food Followed by Abstinence: Emerging Role of Fatty Acid Amide Hydrolase

There is a strong relationship between palatable diet and pain sensitivity, and the cannabinoid and opioid systems might play an important role in this correlation. The palatable diet used in many animal models of obesity is the cafeteria (CAF) diet, based on human food with high sugar, salt, and fat content. In this study, we investigated whether long-term exposure to a CAF diet could modify pain sensitivity and explored the role of the cannabinergic system in this modification. Male Sprague–Dawley rats were divided into two groups: one fed with standard chow only (CO) and the other with extended access (EA) to a CAF diet. Hot plate and tail flick tests were used to evaluate pain sensitivity. At the end of a 40-day CAF exposure, EA rats showed a significant increase in the pain threshold compared to CO rats, finding probably due to up-regulation of CB1 and mu-opioid receptors. Instead, during abstinence from palatable foods, EA animals showed a significant increase in pain sensibility, which was ameliorated by repeated treatment with a fatty acid amide hydrolase inhibitor, PF-3845 (10 mg/kg, intraperitoneally), every other day for 28 days. Ex vivo analysis of the brains of these rats clearly showed that this effect was mediated by mu-opioid receptors, which were up-regulated following repeated treatment of PF-3845. Our data add to the knowledge about changes in pain perception in obese subjects, revealing a key role of CB1 and mu-opioid receptors and their possible pharmacological crosstalk and reinforcing the need to consider this modulation in planning effective pain management for obese patients.

Obesity and pain: a systematic review

BACKGROUND/OBJECTIVES

The current systematic review considered research published within the 10 years preceding June 2019, dealing with the topic of obesity and pain. Within the context of the complex biological and behavioral interrelationships among these phenomena, we sought to identify gaps in the literature and to highlight key targets for future transdisciplinary research. The overarching inclusion criteria were that the included studies could directly contribute to our understanding of these complex phenomena.

METHODS

We searched PubMed/Medline/Cochrane databases dating back 10 years, using the primary search terms "obesity" and "pain," and for a secondary search we used the search terms "pain" and "diet quality."

RESULTS

Included studies (n = 70) are primarily human; however, some animal studies were included to enhance understanding of related basic biological phenomena and/or where human data were absent or significantly limited.

CONCLUSIONS

Our overall conclusions highlight (1) the mechanisms of obesity-related pain (i.e., mechanical, behavioral, and physiological) and potential biological and behavioral contributors (e.g., gender, distribution of body fat, and dietary factors), (2) the requirement for accurate and reliable objective measurement, (3) the need to integrate biological and behavioral contributors into comprehensive, well-controlled prospective study designs.

Neuropsychological functions of verbal recall and psychomotor speed significantly affect pain tolerance

Background

Effects from cognitive performance on pain tolerance have been documented, however, sample sizes are small and confounders often overlooked. We aimed to establish that performance on neuropsychological tests was associated with pain tolerance, controlling for salient confounders.

Methods

This was a cross‐sectional study nested within the Tromsø‐6 survey. Neuropsychological test performance and the cold pressor test were investigated in 4,623 participants. Due to significant interaction with age, participants were divided into three age groups (<60, ≥60 to <70 and ≥70 years). Cox proportional hazard models assessed the relationship between neuropsychological tests and cold pressure pain tolerance, using hand‐withdrawal as event. The fully adjusted models controlled for sex, education, BMI, smoking status, exercise, systolic blood pressure, sleep problems and mental distress.

Results

In the adjusted models, participants aged ≥70 years showed a decreased hazard of hand withdrawal of 18% (HR 0.82, 95% CI (0.73, 0.92) per standard deviation on immediate verbal recall, and a decreased hazard of 23% (HR 0.77, 95% CI (0.65, 0.08) per standard deviation on psychomotor speed. Participants aged ≥60 to <70 years had a significant decreased hazard of 11% (HR 0.89, 95% CI (0.80, 0.98) per standard deviation on immediate word recall. In participants aged <60 years, there was a decreased hazard of 14% (HR 0.86 95% CI: 0.76, 0.98), per standard deviation on psychomotor speed.

Conclusion

Better performance on neuropsychological tests increased pain tolerance on the cold pressor test. These exposure effects were present in all age groups.

Significance

This paper describes substantial associations between cognitive functioning and cold pressor tolerance in 4,623 participants. Reduced psychomotor speed and poor verbal recall gave greater odds for hand‐withdrawal on the cold pressor task. The associations were stronger in older participants, indicating an interaction with age.

Analgesia nociception index for the assessment of pain in critically ill patients: a diagnostic accuracy study

Background

Behavioural pain tools are used in Intensive Care Unit (ICU) patients unable to self-report their pain-intensity but need sustained efforts to educate and train the ICU team because of the subjective nature of these clinical tools. This study measured the validity and performance of an electrophysiological monitoring tool based on the spectral analysis of heart rate variability, the Analgesia Nociception Index (ANI) which varies from 0 (minimal parasympathetic tone, maximal stress-response and pain) to 100 (maximal parasympathetic tone, minimal stress-response and pain).

Methods

Mean-ANI (ANIm) and Instant-ANI (ANIi) were continuously recorded then compared with the Behavioral Pain Scale (BPS) before, during and after routine care procedures in critically-ill non-comatose patients.

Results

969 assessments were performed in 110 patients. ANIi was the most discriminative pain tool. It was significantly correlated with BPS (r=-0.30; 95%CI -0.37 to -0.25; P<0.001). For an ANIi threshold of 42.5, the sensitivity, specificity, positive and negative predictive values were respectively 61.4%, 77.4%, 37.0%, and 90.4%. Compared with the BPS, ANIi had no significantly different ability to change during turning and tracheal-suctioning but changed significantly more during dressing change. ANIi increased independently with age, obesity and severity of illness, and controlled mechanical-ventilation, vasopressors use and analgesia. ANIi decreased independently when vigilance status and respiratory rate increased. ANIm demonstrated poor psychometric properties to detect pain.

Conclusions

Despite low sensitivity/specificity, ANIi≥43 had a Negative-Predictive-Value of 90%. Hence ANIi may be of highest benefit for excluding significant pain. A randomized controlled trial should compare sedation-analgesia protocols based on ANIi to presently recommended behavioural-pain-tools.

Fatiguing Trunk Flexor Exercise Decreases Pain Sensitivity in Postpartum Women

Background

Low back pain (LBP) is common in the general population and among postpartum women. Abdominal muscle exercise is often used to treat LBP, but it is unknown if fatiguing abdominal muscle exercise can produce exercise-induced hypoalgesia (EIH).

Objectives

To assess pressure pain thresholds (PPTs) at rest and following fatiguing trunk flexor exercise (EIH) in (1) nulligravid and postpartum women to evaluate the impact of pregnancy and childbirth and (2) nulligravid women and men to examine sex differences.

Methods

Seventy healthy adults (31 postpartum women, 23 nulligravid women, 16 men) participated. Postpartum and nulligravid women were tested twice (16-18 weeks apart) to identify changes in EIH with postpartum recovery. PPTs were measured at the nailbed and superior rectus abdominis before and after exercise to investigate systemic and local EIH, respectively. Rectus abdominis muscle thickness was assessed with ultrasound.

Results

Postpartum women reported lower PPTs than nulligravid women at the abdomen (p < 0.05) whereas postpartum women had lower PPTs at the nailbed during the first session only. Men reported higher nailbed PPTs (p = 0.047) and similar PPTs at the abdomen than women (p = 0.294). All groups demonstrated EIH at the abdomen (p < 0.05). Systemic EIH was absent in postpartum and nulligravid women (p > 0.05), while men demonstrated hyperalgesia. Local EIH was positively associated with muscle thickness for men and women, which was not significant at the second timepoint.

Limitations

Acute exercise response may not reflect changes that occur with exercise training.

Conclusion

Fatiguing trunk flexor exercise produced local EIH for all groups including postpartum and nulligravid women. Clinically, trunk exercises may be useful for acute pain relief for clinical populations that are characterized by pain and/or weakness in the abdominal region muscles in populations with abdominal pain syndromes.

Body regional heat pain thresholds using the method of limit and level: a comparative study

PURPOSE

The purpose of this study was to compare cutaneous heat pain thresholds using the method of limit and level.

METHODS

Sixteen young males (23.2 ± 3.2 year, 174.9 ± 4.9 cm, and 70.1 ± 8.6 kg) participated in this study. The thermode temperature increased at a constant rate of 0.1 °C s^-1 from 33 °C for the method of limit, whereas the method of level consisted of 3 s heat pulses increasing from 44 °C to 50 °C in 100 s separated by 5 s intervals. All measurements were conducted on 14 body regions (the forehead, neck, chest, abdomen, upper back, upper arm, forearm, waist, hand, palm, thigh, calf, foot, and sole) in 28 °C, 35% relative humidity.

RESULTS

The results are as follows. Heat pain thresholds were on average 3.2 ± 2.1 °C higher for the method of level than for the method of limit (P < 0.05). Second, the correlation coefficient between values by two methods was 0.819 (P < 0.01). Third, lower body regions (thigh, calf, and sole) had higher heat pain thresholds than upper body regions (chest) by the method of level only (P < 0.05). Fourth, body regional subcutaneous fat thickness showed no relationship with heat pain thresholds except the upper arm.

CONCLUSION

These results indicated that cutaneous heat pain thresholds vary based on the type of heat stimuli and body regions. The method of limit could be applied for predicting accumulated thermal pain starting from moderate heat, whereas the method of level may be applicable for predicting acute heat pain to flames or high heat.

Lean mass mediates the relation between temporal summation of pain and sex in young healthy adults

Background

Previous studies have shown that women experience greater temporal summation (TS) of pain than men using a repetitive thermal stimulus. These studies, however, did not individualize the thermal stimulus to each subject’s thermal pain sensitivity. The aim of this study was to investigate sex differences in TS using an individualized protocol and potential mediators that have been shown to influence TS including physical activity and body composition.

Methods

Fifty young healthy men and women (21 men) participated in the study. Subjects completed TS testing on the right forearm using a repetitive thermal stimulus at a temperature that the subject reported 6/10 pain. Other testing included body composition (lunar iDXA), activity monitoring (Actigraph), and Pain Catastrophizing Scale (PCS).

Results

Women reported greater TS than men (p = 0.019), and TS was correlated with right arm lean mass (r = − 0.36, p = 0.01) and magnification subscale of PCS (r = − 0.32, p = 0.03). Mediation analysis showed a complete mediation for the relation between sex and TS by right arm lean mass (indirect effect = 2.33, 95% BCa CI [0.42, 4.58]) after controlling for the temperature, the magnification subscale of PCS, and the average time spent in moderate to vigorous physical activity.

Conclusion

The results of this study suggest that lean mass is a contributing factor to the sex differences in TS. Future studies should investigate whether interventions that increase lean mass have a positive effect on TS.

Alterations in nociception and morphine antinociception in mice fed a high-fat diet

Currently, more than 78.6 million adults in the United States are obese. A majority of the patient population receiving treatment for pain symptoms is derived from this subpopulation. Environmental factors, including the increased availability of food high in fat and sugar, contribute to the continued rise in the rates of obesity. The focus of this study was to investigate whether long-term exposure to a high-fat, energy-dense diet enhances baseline thermal and inflammatory nociception while reducing sensitivity to morphine-induced antinociception. Antinociceptive and hypothermic responses to morphine were determined in male and female C57BL/6N mice fed either a "western-style" diet high in fat and sucrose (HED) or a standard low-fat chow diet for 15 weeks. Antinociception was assessed using both the hot plate and tail flick tests of acute thermal pain and the formalin test of inflammatory pain. Acute administration of morphine dose-dependently increased antinociception in the hot plate and tail flick assays for mice of both sexes fed chow and HED. However, female mice displayed lower antinociceptive response to morphine compared to males in the tail-flick test. Hypothermic responses to acute morphine were also assessed in mice fed chow or HED. Male and female mice fed chow, and female mice fed HED displayed similar hypothermic responses to morphine. However, males fed HED did not exhibit morphine-induced hypothermia. Tolerance to the antinociceptive and hypothermic effects of morphine was assessed after ten days of repeated daily administration (10mg/kg morphine). Male mice fed chow or HED developed tolerance to morphine in the hot plate test. However, females fed HED did not. In the tail flick assay, only mice fed HED developed tolerance to morphine. All groups showed tolerance to morphine-induced hypothermia. In the formalin test, we found that both male and female mice fed HED had reduced sensitivity to the antinociceptive effects of morphine (6mg/kg). Collectively, these data suggest that sensitivity and tolerance to the antinociceptive effects of morphine may be dependent on diet and sex in the hot plate and tail flick thermal pain models, and that the acute antinociceptive effects of morphine in the formalin inflammatory pain model may also be dependent on these two factors. In addition, diet and sex can influence morphine-induced hypothermia. Exposure to an HED may lead to changes in neuronal signaling pathways that alter nociceptive responses to noxious stimuli in a sex-specific manner. Thus, dietary modifications might be a useful way to impact pain therapy.

High fat diet sensitizes fibromyalgia-like pain behaviors in mice via tumor necrosis factor alpha

Fibromyalgia (FM) and obesity are closely related. However, little is known about how obesity contributes to FM. Importantly, adequate evidence has shown that tumor necrosis factor alpha (TNF-α) plays a critical role in obesity. Thus, we hypothesized that obesity-induced TNF-α release may potentiate FM-associated pain. To test this hypothesis, we investigated the role of TNF-α in the development of FM-like pain in a mouse model of acid saline injection-induced FM. Consistent with previous reports, we showed that repeated acid saline injections induced bilateral mechanical hyperalgesia, and this effect lasted for at least 4 days after acid saline injections. This phenomenon was associated with increased levels of TNF-α in plasma, muscles, and spinal cord. Furthermore, we found that 24 weeks of high fat diet treatment significantly potentiated acid saline-induced bilateral mechanical hyperalgesia. High fat diet-treated mice exhibited robustly increased levels of TNF-α in plasma, muscles, and spinal cord after acid saline injections compared with low fat diet-treated mice. Additionally, using immunofluorescence staining, we found that the number of TNF-α positive cells in dorsal root ganglion (DRG) was increased after acid saline injections, and high fat diet treatment further sensitized this increase. Finally, we reported that acid saline-induced FM-like pain behaviors were abolished in TNFRp55-/- mice, confirming the critical role of TNF-α in the development of FM-like pain. Taken together, our results suggested that high fat diet treatment may sensitize acid saline-induced FM-like pain via increasing TNF-α levels in plasma, muscles, and DRG.

Physical Activity May Be Associated with Conditioned Pain Modulation in Women but Not Men among Healthy Individuals

Background

Conditioned pain modulation (CPM), a phenomenon also known as diffuse noxious inhibitory control, is thought to be affected by various factors, including sex and level of physical activity. However, the involvement of these factors in CPM remains unclear.

Methods

Eighty-six healthy young subjects (M/F, 43/43) participated in this study. Participants were assessed on the basis of their mechanical pressure pain threshold (PPT), CPM response, body mass index (BMI), basal metabolic rate (BMR), and duration of moderate-to-vigorous physical activity (MVPA) over a week, using a motion counter. Response to CPM was evaluated as PPT during painful cold stimulation relative to baseline PPT.

Results

Men showed significantly higher baseline PPT than women; however, this difference was no longer significant after controlling for confounders. Stepwise multiple linear regression analyses revealed BMR to be a significant contributor towards baseline PPT in the entire study population. In contrast, although there were no significant contributors to CPM response among men and in the overall study group, MVPA was positively associated with CPM response among women (β = 0.397).

Conclusions

These results suggest that, among healthy young individuals, CPM response may be associated with moderate-to-vigorous physical activity in women but not in men.

Improvements in Health-Related Quality of Life and Pain: A Cohort Study in Obese Patients After Laparoscopic Sleeve Gastrectomy

OBJECTIVE

The principal aim of the study was to investigate the effect of the sleeve gastrectomy (SG) in the quality of life (QoL) and pain in a population of morbidly obese patients.

METHODS

Seventy-two SG patients were assessed in this descriptive observational study, before the surgery and 6 months after that. We evaluated health-related QoL (Gastrointestinal Quality of Life Index [GIQLI]) and pain (spontaneous low back pain by Numerical Point Rate Scale [NPRS] and pressure pain thresholds [PPTs]).

RESULTS

The results of the analysis of variance (ANOVA) revealed significant improvements in nearly all of the subscales of GIQLI questionnaire after 6 months: gastrointestinal symptoms (P = .01), physical well-being (P < .001), social well-being (P = .03), and total GIQLI score (P < .001), but not for the emotional condition (P = .20). Patients also had improvements in spontaneous low back pain (P = .002), but not in the PPTs in all the body areas explored, including the cervical area, low back, and hands (P > .05).

CONCLUSION

Patients receiving SG improved their health-related QoL and low back pain 6 months after the intervention, but this improvement was not so important for pressure pain thresholds in different body areas.

Effect of Chronic Administration of Obestatin and Its Fragment FNAP-NH2 on Behavioral Activity and Nociceptive Threshold in Rats with Normal and Excess Body Weight

The effects of chronic intranasal administration of 300 nmol/kg obestatin and its fragment FNAP-NH₂ on behavioral activity and nociceptive threshold were examined in male Wistar rats with normal body weight or alimentary obesity. In normal rats, obestatin produced no effect on behavior and nociception, whereas FNAP-NH₂ fragment enhanced risk-taking behavior. Rats with excess body weight demonstrated less pronounced risk-taking behavior and elevated nociceptive threshold in comparison with normal animals, but these differences were abolished by chronic administration of FNAP-NH₂.