A key to dissect the triad of insomnia, chronic pain, and depression

Prevalence and epidemiological characteristics of chronic pain in the Spanish population. Results from the pain barometer

BACKGROUND

Chronic pain (CP) is a public health problem worldwide.

AIM

To update the prevalence of CP and compare the clinical and social characteristics of people with CP with those with non-chronic continuous pain and a group without pain.

METHODS

An observational cross-sectional study was carried out in a representative sample of 7058 adults from the Spanish population. Sociodemographic data, the presence of CP and non-chronic continuous pain, characteristics of pain, limitations on activities of daily living (ADL), the presence and level of anxiety and depression (HADS), quality of life (SF-12v2) and social support (DUKE) were collected. Descriptive and bivariate analyses were performed.

RESULTS

The prevalence of CP was 25.9% (95% CI;24.8-26.9) and that of non-chronic continuous pain was 7.7% (95% CI;7.1-8.3). Women presented a higher prevalence of both CP (30.5% vs. 21.3%) and non-chronic continuous pain (8.8% vs. 6.6%). CP was more common in the group between 55 and 75 years old (30.6%, 95% CI = 28.6-32.6%), non-chronic continuous pain affected most the population between 18 and 34 years old (11.2%, 95% CI = 9.6-12.7%). The median duration of CP was 4 years. The lumbar was the most frequent pain site (58.1%), and 27.1% did not know the cause. A greater frequency of limitations on ADL, more anxiety and depression, and worse quality of life were shown among the subjects with CP.

CONCLUSION

CP affects one in four Spanish people and impairs the mental, physical and social health. Differences exist by sex and age in its frequency. Identifying subjects with non-chronic continuous pain is fundamental to prevent their pain from becoming chronic.

SIGNIFICANCE STATEMENT

Indicating the main aspects where this work adds significantly to existing knowledge in the field, and if appropriate to clinical practice. Due to its high prevalence and impact on quality of life, chronic pain has become one of the main health problems nowadays. Attention must be paid to it both from a clinical and social perspective, trying to raise awareness among the population of its possible causes and consequences. In routine clinical practice, greater consideration is given to groups of people with a higher prevalence of chronic pain, such as women and people with middle age, and with no chronic pain to prevent the appearance of chronic pain.

Perioperative insomnia trajectories and functional outcomes after total knee arthroplasty

ABSTRACT

Longitudinal total knee arthroplasty (TKA) studies indicate that a substantial percentage of patients continue to experience clinically significant pain and functional impairment after surgery. Insomnia has been associated with poorer surgical outcomes; however, previous work has largely focused on long-term postsurgical insomnia. This study builds on previous work by examining sleep and pain outcomes about perioperative insomnia trajectories. Insomnia symptoms (using the Insomnia Severity Index) during the acute perioperative period (2 weeks pre-TKA to 6 weeks post-TKA) were used to classify participants into perioperative insomnia trajectories: (1) No Insomnia (ISI < 8), (2) New Insomnia (baseline < 8; postoperative ≥ 8 or ≥6-point increase), (3) Improved Insomnia (baseline ≥ 8, postoperative < 8 or ≥6-point decrease), and (4) Persistent Insomnia (ISI ≥ 8). Insomnia, pain, and physical functioning were assessed in participants with knee osteoarthritis (n = 173; M age = 65 ± 8.3, 57.8% female) at 5 time points: 2 weeks pre-TKA, post-TKA: 6 weeks, 3 months, 6 months, and 12 months. Significant main effects were seen for insomnia trajectory and time, and trajectory-by-time interactions for postoperative insomnia, pain severity, and physical functioning ( P' s < 0.05). The Persistent Insomnia trajectory had the worst postoperative pain at all follow-ups and marked insomnia and physical functioning impairment post-TKA ( P' s < 0.05). The New Insomnia trajectory had notable long-term insomnia (6 weeks to 6 months) and acute (6 weeks) postoperative pain and physical functioning ( P' s < 0.05). Findings indicated a significant relationship between perioperative insomnia trajectory and postoperative outcomes. Results of this study suggest that targeting presurgical insomnia and preventing the development of acute postoperative insomnia may improve long-term postoperative outcomes, with an emphasis on persistent perioperative insomnia due to poorer associated outcomes.

Exercise therapy for chronic pain: How does exercise change the limbic brain function?

We are exposed to various external and internal threats which might hurt us. The role of taking flexible and appropriate actions against threats is played by "the limbic system" and at the heart of it there is the ventral tegmental area and nucleus accumbens (brain reward system). Pain-related fear causes excessive excitation of amygdala, which in turn causes the suppression of medial prefrontal cortex, leading to chronification of pain. Since the limbic system of chronic pain patients is functionally impaired, they are maladaptive to their situations, unable to take goal-directed behavior and are easily caught by fear-avoidance thinking. We describe the neural mechanisms how exercise activates the brain reward system and enables chronic pain patients to take goal-directed behavior and overcome fear-avoidance thinking. A key to getting out from chronic pain state is to take advantage of the behavioral switching function of the basal nucleus of amygdala. We show that exercise activates positive neurons in this nucleus which project to the nucleus accumbens and promote reward behavior. We also describe fear conditioning and extinction are affected by exercise. In chronic pain patients, the fear response to pain is enhanced and the extinction of fear memories is impaired, so it is difficult to get out of "fear-avoidance thinking". Prolonged avoidance of movement and physical inactivity exacerbate pain and have detrimental effects on the musculoskeletal and cardiovascular systems. Based on the recent findings on multiple bran networks, we propose a well-balanced exercise prescription considering the adherence and pacing of exercise practice. We conclude that therapies targeting the mesocortico-limbic system, such as exercise therapy and cognitive behavioral therapy, may become promising tools in the fight against chronic pain.

Association of Sleep Deprivation and the Risk of Developing Systemic Lupus Erythematosus Among Women

OBJECTIVE

Sleep deprivation has been associated with risk of autoimmune diseases. Using the Nurses' Health Study (NHS) (1986-2016) and NHSII (1989-2017) cohorts, we aimed in the present study to investigate whether sleep deprivation was associated with risk of developing systemic lupus erythematosus (SLE).

METHODS

Average sleep duration in a 24-hour period was reported in the NHS (1986-2014) and NHSII (1989-2009). Lifestyle, exposure, and medical information was collected on biennial questionnaires. Adjusted Cox regression analyses modeled associations between cumulative average sleep duration (categorical variables) and incident SLE. Interactions between sleep duration and shiftwork, bodily pain (using the Short Form 36 [SF-36] questionnaire), and depression were examined.

RESULTS

We included 186,072 women with 187 incident SLE cases during 4,246,094 person-years of follow-up. Chronic low sleep duration (≤5 hours/night versus reference >7-8 hours) was associated with increased SLE risk (adjusted hazard ratio [HRadj ] 2.47 [95% confidence interval (95% CI) 1.29, 4.75]), which persisted after the analysis was lagged (4 years; HRadj 3.14 [95% CI 1.57, 6.29]) and adjusted for shiftwork, bodily pain, and depression (HRadj 2.13 [95% CI 1.11, 4.10]). We detected additive interactions between low sleep duration and high bodily pain (SF-36 score <75) with an attributable proportion (AP) of 64% (95% CI 40%, 87%) and an HR for SLE of 2.97 (95% CI 1.86, 4.75) for those with both risk factors compared to those with neither. Similarly, there was an interaction between low sleep duration and depression, with an AP of 68% (95% CI 49%, 88%) and an HR for SLE of 2.82 (95% CI 1.64, 4.85).

CONCLUSION

Chronic low sleep duration was associated with higher SLE risk, with stronger effects among those with bodily pain and depression, highlighting the potential role of adequate sleep in disease prevention.

Impact of pain severity on functioning domains, sleep, and cognition in painful diabetic peripheral polyneuropathy patients

Background

Several studies have observed that painful diabetic peripheral polyneuropathy (PDPN) had an impact on the level of functioning domains and quality of sleep as well as cognitive functions. This study is aimed to explore the relationship between severity of pain and level of functioning, sleep quality, and cognitive functions among these patients. We recruited 100 diabetics with a mean HbA1C% of 7.3±0.9, diagnosed with PDPN, and included in the study with a mean age of 51±12.8 years and disease duration of 10.2±7.4 years. The following assessment was done for each patient; clinical and neurophysiology assessment, routine laboratory assessment, measuring pain severity, and average pain severity interference scores using pain visual analog scale (VAS) and brief pain inventory (BPI) short form, respectively, sleep quality assessment using Pittsburgh Sleep Quality Index (PSQI) and Montreal cognitive function assessment (MOCA) scales.

Results

Moderate to severe pain was recorded in 71% of patients according to the VAS pain score. The severe pain group recorded the significant highest average pain severity and interference scores in BPI and domains compared to other less pain groups with average pain intensity scores of 7.5±0.6 vs 5.3±0.8 in the moderate and 3.3±0.4 in mild pain groups. Poor sleep quality and pattern were observed in these patients with a mean PSQI score of 6.8±3.1, and the severe pain group had a significant highest score of 9.4±2.3 compared to other less group scores of 7±2.3 and 3.7±1.8. Their mean MOCA score was low 24.2±2.2. Out of them 48/100 patients had mild cognitive impairment and recorded high frequency in the severe pain group (28/32) followed by the moderate pain (15/39) group. There is a significant correlation between the score of VAS and PSQI as well as MOCA.

Conclusions

Painful DPN patients had a poor level of functioning and sleep quality as well as cognitive impairment based on pain intensity.

Trial registration

This study was registered on a clinical trial with registration number NCT03275233 on 7 September 2017.

Co-occurrence of chronic pain, depressive symptoms, and poor sleep quality in a health check-up population in China:A multicenter survey

OBJECTIVES

This study aimed to investigate the cooccurrence of chronic pain (CP), depressive symptoms, and poor sleep quality in terms of prevalence and associated factors in a nationwide health check-up population in China.

METHODS

This multicenter cross-sectional survey was performed in 2017. All the participants aged ≥18 years from eight health check-up institutions in 6 provinces and cities were invited to complete a self-report health questionnaire through online resources.

RESULTS

132,444 participants completed the online survey and the overall prevalence of CP and that of the three symptoms were 11.0% (95% confidence interval [95% CI]: 10.8-11.1) and 2.7% (95% CI: 2.6-2.8), respectively. The cooccurrence of all three symptoms increased with age, being higher in the female, widowed, unemployed, and lower education level groups. The respondents with multiple symptoms reported poorer self-rated health. Binary logistic regression analyses identified female sex (adjusted odds ratio [aOR]: 1.51; 95% CI: 1.42-1.62), a widowed status (aOR: 1.39; 95% CI: 1.04-1.84), a lower education level (aORs ranging from 1.46 to 2.47), and having one or more chronic diseases (aORs ranging from 1.43 to 2.02) to be significantly associated with reporting all three symptoms (all P ˂0.05). While long-term medication and regular exercise were the protective factors.

CONCLUSION

This study suggests that the cooccurrence of the three symptoms accounts for a certain proportion of the Chinese health check-up population. Integrated interventions that address CP and mental health cooccurrence may be an essential target for heath management in this population to tackle this considerable burden.

The Effect of Pain Catastrophizing on Depression among Older Korean Adults with Chronic Pain: The Mediating Role of Chronic Pain Interference and Sleep Quality

Pain catastrophizing is a notable concept associated with change in chronic pain interference and depression. Sleep quality is also one of the important factors affecting geriatric depression. This study examined the mediating effects of chronic pain interference and sleep quality on the relationship between pain catastrophizing and depression. This study is a secondary data analysis that analyzed a total of 138 older Korean adults with chronic pain. The participants were selected from a single elderly daycare center in a city in South Korea. Also, the multiple regression analysis and PROCESS macro with bootstrapping were used. The results revealed that chronic pain interference and sleep quality mediated the relationship between pain catastrophizing and depression, respectively. Furthermore, chronic pain interference and sleep quality sequentially and dually mediated the effect of pain catastrophizing on depression. In the management of depression in the elderly, persistent complaints of pain should not be disregarded, irrespective of the intensity of their chronic pain. Psychological intervention is needed to alleviate negative thoughts about chronic pain and to increase the ability to cope with chronic pain. In addition, it is important to assess sleep patterns and to develop interventions to improve sleep quality, because depression in the elderly could appear as a symptom of a sleep problems.

Independent and synergistic effects of pain, insomnia, and depression on falls among older adults: a longitudinal study

Background

Few studies have examined the relationship between falls and pain, insomnia and depressive symptoms which are common and risk factors in older adults. We aimed to examine the independent and synergistic effects of these risk factors on future falls among older adults.

Methods

We used data of 2558 community-dwelling older adults from 2011 (Y1) to 2015 (Y5) of the National Health and Aging Trends Study (NHATS). Pain was determined by whether participants reported bothersome pain in the last month. Insomnia was assessed by two questions about how often the participants had trouble falling asleep and maintaining sleep. Depressive symptoms were assessed by Patient Health Questionnaire-2. Generalized estimation equation (GEE) models were used to examine the independent effects of pain, insomnia and depressive symptoms at prior-wave (period y-1) on falls at current wave (period y) adjusting for covariates (age, sex, education, race/ethnicity, living arrangement, BMI, smoking, vigorous activities, number of chronic illnesses and hospitalization). The significance of the three-way interaction of these factors (pain*insomnia*depression) was tested using the aforementioned GEE models to determine their synergistic effects on falls.

Results

Overall, the participants were mainly 65–79 years old (68%), female (57%) and non-Hispanic White (70%). At Y1, 50.0% of the participants reported pain, 22.6% reported insomnia and 9.9% reported depressive symptoms. The incidence of falls from Y2 to Y5 was 22.4, 26.0, 28.3, and 28.9%, respectively. Participants with pain (Odds ratio [OR], 95% confidence interval [CI] = 1.36, 1.23–1.50) and depressive symptoms (OR, 95% CI = 1.43, 1.23–1.67) had high rates of falling adjusting for covariates. After further adjustment for insomnia and depressive symptoms, pain independently predicted falls (OR, 95% CI = 1.36, 1.22–1.51). Depressive symptoms also independently predicted falls after further adjusting for pain and insomnia (OR, 95% CI = 1.40, 1.20–1.63). After adjusting for pain and depression, the independent effects of insomnia were not significant. None of the interaction terms of the three risk factors were significant, suggesting an absence of their synergistic effects.

Conclusions

Pain and depressive symptoms independently predict falls, but synergistic effects seem absent. Further research is needed to develop effective strategies for reducing falls in older adults, particularly with pain and depressive symptoms.

Sleep Characteristics in Diabetic Patients Depending on the Occurrence of Neuropathic Pain and Related Factors

This study aims to compare the sleep characteristics (structure and quality) in patients with type-2 diabetes mellitus with and without diabetic neuropathic pain (DNP), and to investigate the relationship of sensory phenotypes, anxiety, and depression with sleep quality in DNP patients. A cross-sectional study was performed in patients with type-2 diabetes mellitus and neuropathy. Patients were classified into two groups-with or without neuropathic pain-according to the "Douleur Neuropathique-4 (DN4)" scale. Sleep characteristics and quality (Medical Outcomes Study-MOS-sleep), pain phenotype (Neuropathic Pain Symptom Inventory-NPSI), mood status (Hospital Anxiety and Depression scale-HADS), pain intensity (Visual Analogue Scale-VAS), and quality of life (SF-12v2) were measured. The sample included 130 patients (65 with DNP). The mean scores in all the dimensions of the MOS-sleep scale were higher (more disturbances) in the DNP patients. Higher scores in anxiety or depression, greater intensity of pain or a higher score in the paroxysmal pain phenotype were associated with lower sleep quality in DNP patients. A shorter duration of the diabetes and lower levels of glycated hemoglobin were also associated with lower sleep quality. The results show the relationship between DNP and sleep quality, and the importance of assessing sensory phenotypes and mental comorbidities in these patients. Taking these factors into consideration, to adopt a multimodal approach is necessary to achieve better clinical results.

Relationship between diabetic neuropathic pain and comorbidity. Their impact on pain intensity, diabetes complications and quality of life in patients with type-2 diabetes mellitus

OBJECTIVE

To compare cognitive function, mood and sleep status in patients with and without diabetic neuropathic pain (DNP) and their relationship with pain intensity, diabetes complications, and quality of life. To determine whether these relationships differ depending on the sensorial phenotype.

METHODS

Cross-sectional study performed on patients with type-2 diabetes-mellitus and neuropathy. Presence of DNP, pain intensity and phenotype, mood status, sleep characteristics and quality of life were measured.

RESULTS

A total of 130 patients (65 with DNP) were included. DNP was related to poor sleep quality (OR = 1.03;CI95%:1.02-1.05), pain treatment (OR = 3.00,CI95%:1.24-7.29) or previous anxiety (OR = 2.70,CI95%:1.05-6.99). Patients with specific phenotypes or depression (=0.82,CI95%:-0.02-1.67) referred more severe pain. More complications were related to older age (OR = 1.40,CI95%:1.12-1.66), higher pain intensity (OR = 1.51,CI95%:1.00-2.28), lower cognitive performance (OR = 1.25,CI95%:1.09-1.43), previous anxiety (OR = 10.48,CI95%:1.46-75.24) and insulin treatment (OR = 124.50,CI95%:6.64-2335.06). Decrease in mental quality of life was associated with sleep disorders (β = -0.33,CI95%:-0.48,-0.23), physical comorbidities (β = -9.73,CI95%:-18.15, -1.31) and previous anxiety (β = -7.91,CI95%:-13.04, -2.77). Lower scores in physical quality of life were related to sleep disorders (β = -0.12,CI95%:-0.21, -0.18), obesity (β = -8.35,CI95%:-13.16, -3.55), longer time since diagnosis (β = -0.72,CI95%:-1.44;0.01) and disability (β = -14.58,CI95%:-24.69; -4.48).

CONCLUSIONS

The results support the idea that mental comorbidity and sleep disorders are factors associated with DNP and greater pain intensity, more diabetes complications and lower quality of life. Moreover, they highlight the relationship between sensorial phenotypes and pain intensity, and lower cognitive performance and diabetes complications.

Anxiety, depression and sleep disorders in patients with diabetic neuropathic pain: a systematic review

Introduction: Diabetic neuropathic pain (DNP) is a disabling complication suffered by patients with diabetic neuropathy. DNP coexists with different conditions, especially mental and sleep disorders, which seem to impair the management and course of the disease. However, there is a lack of accurate results about their prevalence. Consequently, the authors analyze the prevalence of anxiety, depression and/or sleep disorders in DND patients.Areas covered: Among the 206 articles found in the search, 8 studies with data from 5 different countries fulfilled the inclusion criteria. The prevalence of anxiety reported ranged between 7.8%-60.4% and that of depression between 13.6%- 50.6%. The two conditions coexist in 26.4%-30.6% in DND patients. A higher prevalence was found when the information was obtained using scales than when it came from medical records. The prevalence of sleep disorders found ranged from 41.6%-43.8%. However, there is lack of information about and the results are often expressed using the mean scores of the scales.Expert opinion: Although the data in the literature vary, a high prevalence of anxiety, depression and sleep comorbidities exists among patients with DNP. These results reaffirm the need to perform systematic evaluations and to identity their presence using validated instruments to obtain more reliable results.

High prevalence of toothache among Great East Japan Earthquake survivors living in temporary housing

OBJECTIVES

The Great East Japan Earthquake and subsequent tsunami cause large-scale destruction in the north-eastern coastal areas in Japan, and forced many survivors to relocate to prefabricated temporary housing, a typical emergency accommodation. Based on the hypothesis that higher toothache prevalence among the disaster survivors is associated with postdisaster distress, we determined the impact of temporary residential environment as potential stressor on the subjective toothache prevalence.

METHODS

A repeated cross-sectional health survey based on self-reported questionnaire was conducted in 2776 disaster survivors, of whom 1446 participants underwent dental examination by dentists. Housing type was categorized into three groups including the same housing as before the earthquake, temporary housing and rented/new housing. The association of housing type with subjective toothache prevalence was examined using multivariate logistic regression analysis in all subjects and subgroup analysis in dental examination applicants. Stratified analysis by survey wave was applied with inclusion of covariates such as the socio-demographic factors, and presence of insomnia and psychological distress. In subgroup analysis, presence of dental caries and gum problems in dental examination were included as factors of direct exposure to subjective toothache.

RESULTS

In the first survey wave, the participants living in the temporary housing had significantly higher odds ratio (OR) for toothache prevalence compared to the participants living in the same housing (OR: 3.76, 95% confidence interval [CI]: 1.85-7.65, P < 0.001); whereas in all other survey waves, there was no significant difference. Subgroup analysis of dental examination applicants confirmed the presence of significant association of subjective toothache prevalence in the temporary housing group alone (OR: 3.27, 95% CI: 1.38-7.76, P = 0.004), but not in the rented/new housing group (OR: 1.50, 95% CI: 0.57-3.91, P = 0.411), even after adjusting for covariates related to oral findings.

CONCLUSION

Temporary housing may be a factor to increase the risk of subjective toothache among disaster survivors only at postdisaster acute phase.

The Relationship Between Tryptophan Hydroxylase-2 Gene with Primary Insomnia and Depressive Symptoms in the Han Chinese Population

Background:

Insomnia often coexists with depression, and there is compelling evidence for a genetic component in the etiologies of both disorders.

Aims:

To investigate the relationship between exonic variant (rs4290270) in the tryptophan hydroxylase-2 gene and primary insomnia and symptoms of depression in Han Chinese.

Study Design:

Case-control study.

Methods:

This study included 152 patients with primary insomnia and 164 age- and gender-matched normal controls. All patients were investigated by polysomnography for 2 consecutive nights. The depressive symptoms were measured by using a 20-item Zung Self-rating Depression Scale. Sleep quality was assessed with the Pittsburgh Sleep Quality index. The genotypes of the TPH-2 gene polymorphism rs4290270 were determined by the polymerase chain reaction-restriction fragment length polymorphism method.

Results:

The genotype distributions of the tryptophan hydroxylase-2 gene polymorphism rs4290270 were in Hardy-Weinberg equilibrium in both patients and controls (p>0.05). The allele and genotype distributions of this variant were comparable between patients and controls in all subjects and between genders (all p>0.05). The impact of rs4290270 on self-rating depression scale score changes was statistically significant (p=0.002), with carriers of the A/A genotype having the highest self-rating depression scale score (mean ± standard deviation: 52.73±12.88), followed by the A/T genotype (50.94±11.29, p=0.35) and the T/T genotype (43.48±7.78, p<0.01), and this impact was more obvious in women (p<0.001).

Conclusion:

The tryptophan hydroxylase-2 gene polymorphism rs4290270 may not be a susceptibility locus for primary insomnia in Han Chinese, but it may be a marker of depressive symptoms.

Bidirectional association between disturbed sleep and neuropathic pain symptoms: a prospective cohort study in post-total joint replacement participants

Background

Disturbed sleep is strongly correlated with chronic pain. The aim of this study was to examine the association between sleep disturbance and incident joint pain focusing on neuropathic-like pain symptoms.

Methods

A total of 423 individuals who had undergone total joint replacement (TJR) for osteoarthritis were assessed at the mean time of 3.6 years post-surgery and again at 5.9 years post-TJR, using the Medical Outcomes Survey sleep subscale, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and painDETECT questionnaire instruments. Cox hazard ratios (HRs) and 95% confidence intervals (CIs) were computed adjusting for age, body mass index, sex, and use of hypnotic and analgesic medication.

Results

The presence of neuropathic pain symptoms predicted incidence of disturbed sleep after adjustment for covariates and pain severity (adjusted HR [aHR] 2.01, 95% CI: 1.00–4.10; p<0.05). There was no association between joint pain and incidence of disturbed sleep when individuals with neuropathic pain symptoms at the baseline visit were excluded (aHR 1.11, 95% CI: 0.47–2.67). Disturbed sleep at baseline predicted incident neuropathic joint pain symptoms (aHR 2.75, 95% CI: 1.21–6.26; p<0.016) but had no effect on incidence of joint pain when all types of pain were considered together (aHR 0.63, 95% CI: 0.30–1.39).

Conclusion

These data suggest a causal bidirectional link between sleep disturbance and joint pain with neuropathic features but not with other types of joint pain.

Understanding the different relationships between mood and sleep disorders in several groups of non-oncological patients with chronic pain

OBJECTIVE

To compare sleep dimensions in patients suffering from chronic pain of different origins, and with a group of pain-free subjects. To analyze the relationship between depression and/or anxiety and sleep disorders in musculoskeletal, neuropathic, and fibromyalgia patients.

METHODS

This cross-sectional study included patients diagnosed with neuropathic pain (NP) (n = 104), musculoskeletal pain (MSK) (n = 99), or fibromyalgia (FM) (n = 51), and pain free subjects (n = 72). Information about sleep dimensions (MOS-sleep), duration and intensity of pain (Visual Analog Scale), and anxiety and depression (Hospital Anxiety and Depression scale) was collected.

RESULTS

Of the 254 patients with chronic pain (PCP) studied, the mean pain intensity was 6.6 (SD = 1.9), with an average duration of 9 years. The scores in all sleep dimensions of the MOS-sleep were higher in CPP (more disturbances) compared to pain free patients, and differences were observed among the three groups of PCP, with FM most severely affected. Anxiety (β = 1.3), depression (β = 1.1), intensity (β = 1.7), and duration of pain (β = 0.04) were associated with more sleep problems in MSK patients. In contrast, anxiety (β = 2.5) and duration of pain (β = 0.05) were negatively related to sleep in the NP patients, and only depression (β = 1.3) affected FM patients.

CONCLUSIONS

The sleep pattern differs among groups of PCP in the presence or absence of mood disorders. Understanding these disorders in each specific group of PCP is fundamental, and it can contribute to improve the clinical situation of the patients and better orientating therapeutic strategies.

A new aspect of chronic pain as a lifestyle-related disease

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Activation of mesolimbic dopamine system underlies exercise-induced hypoalgesia.

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Interaction between mesolimbic system and hypothalamus determines physical activity.

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Changing the lifestyle inactive to active may attenuate and prevent chronic pain.

Physical exercise has been established as a low-cost, safe, and effective way to manage chronic intractable pain. We investigated the underlying mechanisms of exercise-induced hypoalgesia (EIH) using a mouse model of neuropathic pain (NPP). Epigenetic changes in activated microglia and maintained GABA synthesis in the spinal dorsal horn may contribute to EIH. Voluntary exercise (VE), a strong reward for animals, also induced EIH, which may be due in part to the activation of dopamine (DA) neurons in the ventral tegmental area (VTA). VE increases the expression of pCREB in dopaminergic neurons in the VTA, which would enhance dopamine production, and thereby contributes to the activation of the mesolimbic reward system in NPP model mice. We demonstrated that neurons in the laterodorsal tegmental and pedunculopontine tegmental nuclei, a major input source of rewarding stimuli to the VTA, were activated by exercise.

Chronic pain is at least partly attributed to sedentary and inactive lifestyle as indicated by the Fear-avoidance model. Therefore, chronic pain could be recognized as a lifestyle-related disease. Physical activity/inactivity may be determined by genetic/epigenetic and neural factors encoded in our brain. The hypothalamus and reward system is closely related in the axis of food intake, energy metabolism and physical activity. Understanding the interactions between the mesolimbic DA system and the hypothalamus that sense and regulate energy balance is thus of significant importance. For example, proopiomelanocortin neurons and melanocortin 4 receptors may play a role in connecting these two systems. Therefore, in a certain sense, chronic pain and obesity may share common behavioral and neural pathology, i.e. physical inactivity, as a result of inactivation of the mesolimbic DA system. Exercise and increasing physical activity in daily life may be important in treating and preventing chronic pain, a life-style related disease.

Causal Mediation in the Development of Painful Temporomandibular Disorder

We explored causal mediation of sleep quality and perceived stress in development of painful temporomandibular disorder (TMD). Sleep quality and perceived stress were assessed at baseline and quarterly intervals thereafter in 2,737 initially TMD-free adults in the Orofacial Pain Prospective Evaluation and Risk Assessment study (OPPERA) prospective cohort study. During follow-up, incident TMD cases were classified using research diagnostic criteria. Mediation analysis was conducted using a weighted Cox proportional hazards regression model that estimated hazard ratios (HRs) and 95% confidence limits (CL) of first-onset TMD. Models determined whether: 1) poor sleep quality during follow-up mediated the effect of baseline perceived stress on first-onset TMD, and 2) perceived stress during follow-up mediated the effect of baseline poor sleep quality on first-onset TMD. In both analyses, the total effect was decomposed into natural direct and indirect effects. Poor baseline sleep quality led to heightened perceived stress that then contributed to TMD development. When the total effect of poor sleep quality (HR = 2.10, CL = 1.76, 2.50) was decomposed, 34% of its effect was mediated by perceived stress (indirect effect HR = 1.29, CL = 1.06, 1.58). The effect of perceived stress on first-onset TMD was not mediated by sleep quality. Improving sleep may avert escalation of stress, limiting effects of both factors on TMD development.

PERSPECTIVE

Causal mediation analysis highlights mechanisms by which poor sleep quality promotes development of TMD. First, poor sleep quality exerts a direct effect on pain. Second, it triggers a heightened perception of stress, which acts as an intermediate factor in the causal pathway between poor sleep quality and first-onset TMD pain.