The association of sleep and pain: an update and a path forward

Familial Contributions to Self-Reported Sleep and Pain in Female Twins

OBJECTIVE

The relationship between sleep quality and pain has been studied in populations with chronic pain and in nonclinical populations using experimental paradigms. Little is known about the familial contributions to this relationship. This study examines self-reported sleep quality and pain in a nonclinical sample and to explore familial (i.e., shared genetic and common family environment) confounding in those relationships.

DESIGN

Cross-sectional.

SUBJECTS

Ninety nine community-based female twin pairs (N = 198) with a mean age of 29 years; 72% monozygotic.

METHODS

The short form McGill Pain Questionnaire (McGill), a visual analog scale (VAS), a body map, and the Pittsburgh Sleep Quality Index (PSQI) measured self-reported pain and sleep quality. Mixed model regression adjusted for age was used to examine relationships between the pain indices and PSQI in overall and within-pair models.

RESULTS

Higher PSQI total scores were significantly associated with higher scores across the McGill sensory (B = 0.37, p < 0.001), affective (B = 0.16, p < 0.001), total scores (B = 0.54, p < 0.001), the VAS (B = 2.41, p < 0.001), and number of sites with any pain on the body map (B = 0.42, p = 0.001). All of these associations were diminished and rendered nonsignificant in within-pair analyses that accounted for genetic and familial factors (all p's ≥ 0.01; Bonferroni α = 0.01).

CONCLUSIONS

These findings support an association between poor sleep quality and pain and suggest that this relationship may be confounded by shared genetic and environmental factors, which could elucidate biological mechanisms that underlie the development and maintenance of pain and sleep problems.

Markov chain evaluation of acute postoperative pain transition states

Previous investigations on acute postoperative pain dynamicity have focused on daily pain assessments, and so were unable to examine intraday variations in acute pain intensity. We analyzed 476,108 postoperative acute pain intensity ratings, which were clinically documented on postoperative days 1 to 7 from 8346 surgical patients using Markov chain modeling to describe how patients are likely to transition from one pain state to another in a probabilistic fashion. The Markov chain was found to be irreducible and positive recurrent, with no absorbing states. Transition probabilities ranged from 0.0031, for the transition from state 10 to state 1, to 0.69 for the transition from state 0 to state 0. The greatest density of transitions was noted in the diagonal region of the transition matrix, suggesting that patients were generally most likely to transition to the same pain state as their current state. There were also slightly increased probability densities in transitioning to a state of asleep or 0 from the current state. An examination of the number of steps required to traverse from a particular first pain score to a target state suggested that overall, fewer steps were required to reach a state of 0 (range 6.1-8.8 steps) or asleep (range 9.1-11) than were required to reach a mild pain intensity state. Our results suggest that using Markov chains is a feasible method for describing probabilistic postoperative pain trajectories, pointing toward the possibility of using Markov decision processes to model sequential interactions between pain intensity ratings, and postoperative analgesic interventions.

Multiple Levels of Suffering: Discrimination in Health-Care Settings is Associated With Enhanced Laboratory Pain Sensitivity in Sickle Cell Disease

OBJECTIVE

People living with sickle cell disease (SCD) experience severe episodic and chronic pain and frequently report poor interpersonal treatment within health-care settings. In this particularly relevant context, we examined the relationship between perceived discrimination and both clinical and laboratory pain.

METHODS

Seventy-one individuals with SCD provided self-reports of experiences with discrimination in health-care settings and clinical pain severity, and completed a psychophysical pain testing battery in the laboratory.

RESULTS

Discrimination in health-care settings was correlated with greater clinical pain severity and enhanced sensitivity to multiple laboratory-induced pain measures, as well as stress, depression, and sleep. After controlling for relevant covariates, discrimination remained a significant predictor of mechanical temporal summation (a marker of central pain facilitation), but not clinical pain severity or suprathreshold heat pain response. Furthermore, a significant interaction between experience with discrimination and clinical pain severity was associated with mechanical temporal summation; increased experience with discrimination was associated with an increased correlation between clinical pain severity and temporal summation of pain.

DISCUSSION

Perceived discrimination within health-care settings was associated with pain facilitation. These findings suggest that discrimination may be related to increased central sensitization among SCD patients, and more broadly that health-care social environments may interact with pain pathophysiology.

Report and Research Agenda of the American Geriatrics Society and National Institute on Aging Bedside-to-Bench Conference on Sleep, Circadian Rhythms, and Aging: New Avenues for Improving Brain Health, Physical Health, and Functioning

The American Geriatrics Society, with support from the National Institute on Aging and other funders, held its eighth Bedside-to-Bench research conference, entitled "Sleep, Circadian Rhythms, and Aging: New Avenues for Improving Brain Health, Physical Health and Functioning," October 4 to 6, 2015, in Bethesda, Maryland. Part of a conference series addressing three common geriatric syndromes-delirium, sleep and circadian rhythm (SCR) disturbance, and voiding dysfunction-the series highlighted relationships and pertinent clinical and pathophysiological commonalities between these three geriatric syndromes. The conference provided a forum for discussing current sleep, circadian rhythm, and aging research; identifying gaps in knowledge; and developing a research agenda to inform future investigative efforts. The conference also promoted networking among developing researchers, leaders in the field of SCR and aging, and National Institutes of Health program personnel.

Exploring the Mechanisms of Exercise-Induced Hypoalgesia Using Somatosensory and Laser Evoked Potentials

Exercise-induced hypoalgesia is well described, but the underlying mechanisms are unclear. The aim of this study was to examine the effect of exercise on somatosensory evoked potentials, laser evoked potentials, pressure pain thresholds and heat pain thresholds. These were recorded before and after 3-min of isometric elbow flexion exercise at 40% of the participant's maximal voluntary force, or an equivalent period of rest. Exercise-induced hypoalgesia was confirmed in two experiments (Experiment 1–SEPs; Experiment 2–LEPs) by increased pressure pain thresholds at biceps brachii (24.3 and 20.6% increase in Experiment 1 and 2, respectively; both d > 0.84 and p < 0.001) and first dorsal interosseous (18.8 and 21.5% increase in Experiment 1 and 2, respectively; both d > 0.57 and p < 0.001). In contrast, heat pain thresholds were not significantly different after exercise (forearm: 10.8% increase, d = 0.35, p = 0.10; hand: 3.6% increase, d = 0.06, p = 0.74). Contrasting effects of exercise on the amplitude of laser evoked potentials (14.6% decrease, d = −0.42, p = 0.004) and somatosensory evoked potentials (10.9% increase, d = −0.02, p = 1) were also observed, while an equivalent period of rest showed similar habituation (laser evoked potential: 7.3% decrease, d = −0.25, p = 0.14; somatosensory evoked potential: 20.7% decrease, d = −0.32, p = 0.006). The differential response of pressure pain thresholds and heat pain thresholds to exercise is consistent with relative insensitivity of thermal nociception to the acute hypoalgesic effects of exercise. Conflicting effects of exercise on somatosensory evoked potentials and laser evoked potentials were observed. This may reflect non-nociceptive contributions to the somatosensory evoked potential, but could also indicate that peripheral nociceptors contribute to exercise-induced hypoalgesia.

Excessive daytime sleepiness and fatigue may indicate accelerated brain aging in cognitively normal late middle-aged and older adults

Excessive daytime sleepiness (EDS) and fatigue increases with age. The aim of this study was to investigate the association between EDS and fatigue with cortical thickness and hippocampal volume in cognitively normal, late middle-aged and older adults. We performed a cross-sectional observational study of 1374 cognitively-normal subjects aged 50 years and older who had a structural MRI. Regional cortical thickness and hippocampal volume were measured. Multiple linear regression models were fit to explore associations between EDS and fatigue and structural MRI measures in different brain regions, adjusting for multiple covariates. EDS was defined as Epworth Sleepiness Scale ≥10. Fatigue severity was assessed with the Beck Depression Inventory-2. 208 participants had EDS, 27 had significant fatigue, and 11 had both. Participants with EDS or fatigue had significantly lower cognitive scores, more disturbed sleep, and medical comorbidities. The presence of EDS was associated with both global and regional atrophy, whereas fatigue was more associated with frontal and temporal changes. Cortical thinning predicted by EDS and fatigue was maximal in the temporal region with average reduction of 34.2 μm (95% CI, -54.1, -14.3; P = 0.001) and 90.2 μm (95% CI, -142.1, -38.2; P = 0.001), respectively. Fatigue was also associated with hippocampal volume reduction of -374.2 mm³ (95% CI, -670.8, -77.7; P = 0.013). Temporal cortical thinning predicted by presence of EDS and fatigue was equivalent to more than 3.5 and 9 additional years of aging, respectively. EDS and fatigue were associated with cortical thickness reduction primarily in regions with increased age-susceptibility, which may indicate accelerated brain aging.

The analgesic effect of therapeutic rTMS is not mediated or predicted by comorbid psychiatric or sleep disorders

BACKGROUND

Mechanisms underlying alleviation of neuropathic pain by repetitive transcranial magnetic stimulation (rTMS) of primary motor cortex (M1) and right secondary somatosensory cortex (S2) are only partly known. Patients with chronic neuropathic pain often have comorbidities like depression and sleep problems. Through functional connectivity, rTMS of M1 and S2 may activate dorsolateral prefrontal cortex, the target for treating depression with rTMS. Thus, the analgesic effect of rTMS could be mediated indirectly via improvement of psychiatric comorbidities or sleep. We examined whether rTMS has an independent analgesic effect or whether its clinical benefits depend on effects on mood or sleep. We also evaluated if comorbid psychiatric or sleep disorders predict the treatment outcome.

METHODS

Sixteen patients with chronic drug-resistant neuropathic orofacial pain participated in this randomized controlled crossover rTMS study. Patients' psychiatric history was evaluated by a specialist in psychiatry. Intensity and interference of pain, mood, and the quality of sleep and life were evaluated at baseline and after 2 active (primary somatosensory cortex [S1]/M1 and S2) and placebo rTMS treatments. A logistic regression analysis was done to investigate predictors of treatment outcome.

RESULTS

The analgesic effect of the right S2 stimulation was not associated with improvement of psychiatric conditions or sleep, whereas S1/M1 stimulation improved sleep without significant analgesic effect (P = 0.013-0.046 in sleep scores). Psychiatric and sleep disorders were more common in patients than in the general population (P = 0.000-0.001 in sleep scores), but these comorbidities did not predict the rTMS treatment outcome.

CONCLUSION

We conclude that rTMS to the right S2 does not exert its beneficial analgesic effects in chronic neuropathic orofacial pain via indirect improvement of comorbid psychiatric or sleep disorders.

Repeating patterns of sleep restriction and recovery: Do we get used to it?

Despite its prevalence in modern society, little is known about the long-term impact of restricting sleep during the week and 'catching up' on weekends. This common sleep pattern was experimentally modeled with three weeks of 5 nights of sleep restricted to 4h followed by two nights of 8-h recovery sleep. In an intra-individual design, 14 healthy adults completed both the sleep restriction and an 8-h control condition, and the subjective impact and the effects on physiological markers of stress (cortisol, the inflammatory marker IL-6, glucocorticoid receptor sensitivity) were assessed. Sleep restriction was not perceived to be subjectively stressful and some degree of resilience or resistance to the effects of sleep restriction was observed in subjective domains. In contrast, physiological stress response systems remain activated with repeated exposures to sleep restriction and limited recovery opportunity. Morning IL-6 expression in monocytes was significantly increased during week 2 and 3 of sleep restriction, and remained increased after recovery sleep in week 2 (p<0.05) and week 3 (p<0.09). Serum cortisol showed a significantly dysregulated 24h-rhythm during weeks 1, 2, and 3 of sleep restriction, with elevated morning cortisol, and decreased cortisol in the second half of the night. Glucocorticoid sensitivity of monocytes was increased, rather than decreased, during the sleep restriction and sleep recovery portion of each week. These results suggest a disrupted interplay between the hypothalamic-pituitary-adrenal and inflammatory systems in the context of repeated exposure to sleep restriction and recovery. The observed dissociation between subjective and physiological responses may help explain why many individuals continue with the behavior pattern of restricting and recovering sleep over long time periods, despite a cumulative deleterious physiological effect.

Sleep and Pain in Pediatric Illness: A Conceptual Review

BACKGROUND

Sleep disruption is a common comorbidity of pediatric pain. Consequences of pain and disrupted sleep, evidence for the pain-sleep relation, and how aspects of illness, treatment, and pharmacological pain management may contribute to or exacerbate these issues are presented.

AIMS

This conceptual review explored the relation between pain and sleep in children diagnosed with chronic medical or developmental conditions. The goal of this review is to expand upon the literature by examining common themes in sleep disturbances associated with painful conditions across multiple pediatric illnesses. Populations reviewed include youth with intellectual and developmental disabilities (IDD), migraines, cystic fibrosis (CF), sickle cell disease (SCD), cancer, juvenile idiopathic arthritis (JIA), juvenile fibromyalgia (JFM), and functional gastrointestinal disorders (FGIDs).

RESULTS

Consistent evidence demonstrates that children with medical or developmental conditions are more vulnerable to experiencing pain and subjective sleep complaints than healthy peers. Objective sleep concerns are common but often under-studied. Evidence of the pain-sleep relationship exists, particularly in pediatric SCD, IDD, and JIA, with a dearth of studies directly examining this relation in pediatric cancer, JFM, CF, and FGIDs. Findings suggest that assessing and treating pain and sleep disruption is important when optimizing functional outcomes.

CONCLUSION

It is essential that research further examine objective sleep, elucidate the pain-sleep relationship, consider physiological and psychosocial mechanisms of this relationship, and investigate nonpharmacological interventions aimed at improving pain and sleep in vulnerable pediatric populations.

Development of the Pain-Related Beliefs and Attitudes about Sleep (PBAS) Scale for the Assessment and Treatment of Insomnia Comorbid with Chronic Pain

STUDY OBJECTIVES

Dysfunctional beliefs and attitudes about sleep is a cognitive-behavioral factor central to the development and perpetuation of insomnia. Previous works to unravel the complex interrelationship between pain and insomnia have not explored the role of inflexible beliefs about the sleep-pain interaction, possibly due to a lack of a valid instrument for doing so. The current study evaluated the psychometric and functional properties of a 10-item Pain-Related Beliefs and Attitudes about Sleep (PBAS) scale.

METHODS

The PBAS scale was administered to four clinical samples of chronic pain patients with comorbid insomnia: to examine the scale's psychometric properties (n = 137), test-retest reliability (n = 26), sensitivity to treatment (n = 20), and generalizability (n = 62). All participants completed the PBAS together with validated measures of pain interference, insomnia severity, and cognitive-behavioral processes hypothesized to underpin insomnia.

RESULTS

The PBAS scale was found to be reliable, with adequate internal consistency and temporal stability. Factor analysis suggested a 2-factor solution representing beliefs about "pain as the primary cause of insomnia" and the "inevitable consequences of insomnia on pain and coping." The PBAS total score was positively correlated with scores from the Insomnia Severity Index (ISI) scale, Dysfunctional Beliefs and Attitudes about Sleep (DBAS) scale, and the Anxiety and Preoccupation about Sleep Questionnaire (APSQ). It was a significant predictor of insomnia severity and pain interference. A significant reduction in PBAS was also observed in patients after receiving a hybrid cognitive-behavioral intervention for both pain and insomnia.

CONCLUSIONS

Pain-related sleep beliefs appear to be an integral part of chronic pain patients' insomnia experience. The PBAS is a valid and reliable instrument for evaluating the role of these beliefs in chronic pain patients.

Assessment and treatment at a pain clinic: A one-year follow-up of patients with chronic pain

BACKGROUND AND AIMS

Pain is one of the most common reasons for patients to seek primary health care. Pain relief is likely to be achieved for patients suffering from acute pain, but for individuals with chronic pain it is more likely that the condition will persist. These patients have the option of being referred to specialised pain clinics. However, the complexity surrounding chronic pain patients is not well studied in these settings. This study aimed to describe patients with chronic pain referred to a pain clinic by using the information submitted during their first visit and one year later and also to identify associations between baseline characteristics and improvements in health-related quality of life in the follow-up.

METHODS

This was a longitudinal observational study of a sample consisting of 318 patients referred to a pain clinic. One group of patients containing 271 individuals (median age 48, 64% females) was assessed and received conventional pain treatment (CPT group) and a second group of 47 patients (median age 53, 64% females) was assessed by a pain specialist and referred back to their physician with a treatment recommendation (assessment only, AO group). Patient-reported outcome measures in health-related quality of life (EQ-5D), pain intensity (VAS), mental health (HADS), insomnia (ISI), pain-related disability (PDI), kinesiophobia (TSK) and sense of coherence (SOC) were collected at the first visit and one year later.

RESULTS

At baseline, the CPT group reported a low EQ-5D Index (median (md) 0.157) and EQ VAS (md 40) as well as considerable high, current pain intensity VAS (md 58), HADS anxiety (md 8), ISI (md 17), PDI (md 36) and TSK (md 39). The AO group showed similar problems (no significant differences compared to the CPT group), except for ISI, where the AO group reported less severe problems. At the one-year follow-up, the CPT group had a statistically significant improvement in EQ-5D, VAS, ISI, PDI and TSK. In the AO group no significant changes were observed. In the CPT group there was an association between a high ISI level at baseline and an improved EQ-5D Index in the follow-up.

CONCLUSIONS

The study describes rarely explored groups of patients with chronic pain at a pain clinic. Severe pain problems were present in both groups at their first visit. A statistically significant improvement could be seen in the group that was conventionally treated while this was not the case among those subjects who were assessed and referred. The results imply, that relatively limited treatment strategies were helpful for the patients' health-related quality of life. Despite these improvements, the patients were not fully recovered, pointing to the chronicity of pain conditions and the need of support for many patients.

IMPLICATIONS

Increased knowledge about assessment, selection and treatment at pain clinics is important to improve the quality of the work performed at these clinics. Despite limited resources, further efforts should be made to collect comparable, valid data on a regular base from pain clinics in order to develop recommendation models.

The Impact of Massage Therapy on Function in Pain Populations-A Systematic Review and Meta-Analysis of Randomized Controlled Trials: Part III, Surgical Pain Populations

OBJECTIVE

Pain is multi-dimensional and may be better addressed through a holistic, biopsychosocial approach. Massage therapy is commonly practiced among patients seeking pain management; however, its efficacy is unclear. This systematic review and meta-analysis is the first to rigorously assess the quality of the evidence for massage therapy's efficacy in treating pain, function-related, and health-related quality of life outcomes in surgical pain populations.

METHODS

Key databases were searched from inception through February 2014. Eligible randomized controlled trials were assessed for methodological quality using SIGN 50 Checklist. Meta-analysis was applied at the outcome level. A professionally diverse steering committee interpreted the results to develop recommendations.

RESULTS

Twelve high quality and four low quality studies were included in the review. Results indicate massage therapy is effective for treating pain [standardized mean difference (SMD) = -0.79] and anxiety (SMD = -0.57) compared to active comparators.

CONCLUSION

Based on the available evidence, weak recommendations are suggested for massage therapy, compared to active comparators for reducing pain intensity/severity and anxiety in patients undergoing surgical procedures. This review also discusses massage therapy safety, challenges within this research field, how to address identified research gaps, and next steps for future research.

Fibromyalgia: A Critical and Comprehensive Review

Fibromyalgia is a disorder that is part of a spectrum of syndromes that lack precise classification. It is often considered as part of the global overview of functional somatic syndromes that are otherwise medically unexplained or part of a somatization disorder. Patients with fibromyalgia share symptoms with other functional somatic problems, including issues of myalgias, arthralgias, fatigue and sleep disturbances. Indeed, there is often diagnostic and classification overlap for the case definitions of a variety of somatization disorders. Fibromyalgia, however, is a critically important syndrome for physicians and scientists to be aware of. Patients should be taken very seriously and provided optimal care. Although inflammatory, infectious, and autoimmune disorders have all been ascribed to be etiological events in the development of fibromyalgia, there is very little data to support such a thesis. Many of these disorders are associated with depression and anxiety and may even be part of what has been sometimes called affected spectrum disorders. There is no evidence that physical trauma, i.e., automobile accidents, is associated with the development or exacerbation of fibromyalgia. Treatment should be placed on education, patient support, physical therapy, nutrition, and exercise, including the use of drugs that are approved for the treatment of fibromyalgia. Treatment should not include opiates and patients should not become poly pharmacies in which the treatment itself can lead to significant morbidities. Patients with fibromyalgia are living and not dying of this disorder and positive outlooks and family support are key elements in the management of patients.

Child and Family Antecedents of Pain During the Transition to Adolescence: A Longitudinal Population-Based Study

Pediatric persistent pain is associated with poorer physical and psychosocial functioning in children, as well as immediate and long-term societal costs. Onset typically occurs in early adolescence, suggesting that late childhood is a key window for identifying potential intervention targets before pain symptoms become entrenched. This study used population-based data from the Longitudinal Study of Australian Children (n = 3,812) and adopted a biopsychosocial and ecological systems approach to investigate child, family, and sociodemographic factors associated with pain problems in children transitioning to adolescence. The prevalence of at least weekly parent-reported pain in the study sample was approximately 5% at 10 to 11 years of age, and pain continued at 12 to 13 years of age for 40% of these children. Key factors at 10 to 11 years that uniquely predicted parent-reported pain problems at 12 to 13 years were frequency of previous pain (1-3 times weekly: odds ratio [OR] = 7.49; 95% confidence interval [CI], 4.3-13.0; 4-7 times weekly: OR = 17.8; 95% CI, 8.7-36.5) and sleep difficulties (OR = 1.86; 95% CI, 1.16-2.97). This study highlights the importance of early intervention for persistent pain in childhood, because pain complaints in late childhood tend to persist into early adolescence.

PERSPECTIVE

This article used a biopsychosocial and ecological systems approach to understanding predictors of pain problems during the transition to adolescence within a nationally representative community-based cohort. Sleep difficulties at 10 to 11 years uniquely predicted pain at ages 12 to 13 years, suggesting that early intervention using sleep interventions may be a promising direction for future research.

Individual differences in self-reported difficulty sleeping across the menstrual cycle

The effect of menstrual cycle phase on sleep has been studied for decades; however, individual differences in the associations between sleep and menstrual phase have not been well studied. In addition, the associations between changes in sleep and other physiological and psychological factors that vary as a function of menstrual phase have not been thoroughly assessed. This study explored individual differences in daily self-reports of difficulty sleeping across the menstrual cycle, as well as associations between daily changes in difficulty sleeping and psychological/vegetative and somatic symptoms. Participants (n = 213 females, mean age = 21.29 ± 4.01 years) completed daily online questionnaires assessing` sleep, psychological and physical symptoms for two menstrual cycles. Two patterns of menstrual cycle-related self-reported difficulty sleeping emerged in addition to women who showed no cyclical change in self-reported difficulty sleeping: a perimenstrual increase and a mid-cycle increase. All psychological/vegetative symptoms and some of the somatic symptoms showed significant associations with self-reported difficulty sleeping. These findings highlight the importance of examining individual differences in sleep across the menstrual cycle and the significant contribution of a wide range of menstrual cycle-related psychological/vegetative and somatic symptoms.

Polysomnographic Measurement of Sleep Duration and Bodily Pain Perception in the Sleep Heart Health Study

STUDY OBJECTIVES

To determine whether total sleep time (TST) and specific sleep stage duration are associated with bodily pain perception and whether sex, age, or subjective sleepiness modifies this relationship.

METHODS

Data from adults ages 39-90 y (n = 5,199) who took part in the Sleep Heart Health Study Exam 1 were analyzed. TST, rapid eye movement (REM) sleep time, and slow wave sleep (SWS) time were measured by unattended, in-home nocturnal polysomnography. Bodily pain perception was measured via the Short Form-36 questionnaire bodily pain component. We used logistic regression to examine associations between total and individual sleep stage durations and bodily pain perception controlling for age, sex, race, body mass index, apnea-hypopnea index, antidepressant use, and important cardiovascular conditions (smoking [pack-years], history of diabetes, and history of percutaneous coronary intervention and/or coronary artery bypass graft).

RESULTS

In the fully adjusted model, REM sleep time and SWS time were not associated with "moderate to severe pain," whereas TST was: Each 1-h decrement in TST was associated with a 7% increased odds of "moderate to severe pain" (odds ratio 1.07, 95% confidence interval 1.002, 1.14). Due to modification of the association between SWS time and "moderate to severe pain" by sex (P for interaction = 0.01), we performed analyses stratified by sex: Each 1-h decrement in SWS time was associated with a 20% higher odds of "moderate to severe pain" among men (odds ratio 1.20, 95% confidence interval 1.03-1.42) whereas an association was not observed among women.

CONCLUSIONS

Shorter TST among all subjects and shorter SWS time in men was associated with "moderate to severe pain." REM sleep time was not associated with bodily pain perception in this cohort.

The Impact of Massage Therapy on Function in Pain Populations-A Systematic Review and Meta-Analysis of Randomized Controlled Trials: Part I, Patients Experiencing Pain in the General Population

PURPOSE

Pain is multi-dimensional and may be better addressed through a holistic, biopsychosocial approach. Massage therapy is commonly practiced among patients seeking pain management; however, its efficacy is unclear. This systematic review and meta-analysis is the first to rigorously assess the quality of massage therapy research and evidence for its efficacy in treating pain, function-related and health-related quality of life outcomes across all pain populations.

METHODS

Key databases were searched from inception through February 2014. Eligible randomized controlled trials were assessed for methodological quality using SIGN 50 Checklist. Meta-analysis was applied at the outcome level. A diverse steering committee interpreted the results to develop recommendations.

RESULTS

Sixty high quality and seven low quality studies were included in the review. Results demonstrate massage therapy effectively treats pain compared to sham [standardized mean difference (SMD) = -.44], no treatment (SMD = -1.14), and active (SMD = -0.26) comparators. Compared to active comparators, massage therapy was also beneficial for treating anxiety (SMD = -0.57) and health-related quality of life (SMD = 0.14).

CONCLUSION

Based on the evidence, massage therapy, compared to no treatment, should be strongly recommended as a pain management option. Massage therapy is weakly recommended for reducing pain, compared to other sham or active comparators, and improving mood and health-related quality of life, compared to other active comparators. Massage therapy safety, research challenges, how to address identified research gaps, and necessary next steps for implementing massage therapy as a viable pain management option are discussed.

Ultralow Dose of Naloxone as an Adjuvant to Intrathecal Morphine Infusion Improves Perceived Quality of Sleep but Fails to Alter Persistent Pain: A Randomized, Double-blind, Controlled Study

Supplemental Digital Content is available in the text.

Introduction:

This randomized, cross-over, double-blind, controlled study of continuous intrathecal morphine administration in patients with severe, long-term pain addresses whether the supplementation of low doses of naloxone in this setting is associated with beneficial clinical effects.

Methods:

All of the study subjects (n=11) provided informed consent and were recruited from a subset of patients who were already undergoing long-term treatment with continuous intrathecal morphine because of difficult-to-treat pain. The patients were (in a randomized order) also given intrathecal naloxone (40 ng/24 h or 400 ng/24 h). As control, the patients’ ordinary dose of morphine without any additions was used. The pain (Numeric Rating Scale, NRS) during activity, perceived quality of sleep, level of activity, and quality of life as well as the levels of several proinflammatory and anti-inflammatory cytokines in the blood were assessed. The prestudy pain (NRS during activity) in the study group ranged from 3 to 10.

Results:

A total of 64% of the subjects reported improved quality of sleep during treatment with naloxone at a dose of 40 ng per 24 hours as compared with 9% with sham treatment (P=0.024). Although not statistically significant, pain was reduced by 2 NRS steps or more during supplemental treatment with naloxone in 36% of subjects when using the 40 ng per 24 hours dose and in 18% of the subjects when using naloxone 400 ng per 24 hours dose. The corresponding percentage among patients receiving unaltered treatment was 27%.

Conclusions:

To conclude, the addition of an ultralow dose of intrathecal naloxone (40 ng/24 h) to intrathecal morphine infusion in patients with severe, persistent pain improved perceived quality of sleep. We were not able to show any statistically significant effects of naloxone on pain relief, level of activity, or quality of life.

Painful Temporomandibular Disorder: Decade of Discovery from OPPERA Studies

In 2006, the OPPERA project (Orofacial Pain: Prospective Evaluation and Risk Assessment) set out to identify risk factors for development of painful temporomandibular disorder (TMD). A decade later, this review summarizes its key findings. At 4 US study sites, OPPERA recruited and examined 3,258 community-based TMD-free adults assessing genetic and phenotypic measures of biological, psychosocial, clinical, and health status characteristics. During follow-up, 4% of participants per annum developed clinically verified TMD, although that was a "symptom iceberg" when compared with the 19% annual rate of facial pain symptoms. The most influential predictors of clinical TMD were simple checklists of comorbid health conditions and nonpainful orofacial symptoms. Self-reports of jaw parafunction were markedly stronger predictors than corresponding examiner assessments. The strongest psychosocial predictor was frequency of somatic symptoms, although not somatic reactivity. Pressure pain thresholds measured at cranial sites only weakly predicted incident TMD yet were strongly associated with chronic TMD, cross-sectionally, in OPPERA's separate case-control study. The puzzle was resolved in OPPERA's nested case-control study where repeated measures of pressure pain thresholds revealed fluctuation that coincided with TMD's onset, persistence, and recovery but did not predict its incidence. The nested case-control study likewise furnished novel evidence that deteriorating sleep quality predicted TMD incidence. Three hundred genes were investigated, implicating 6 single-nucleotide polymorphisms (SNPs) as risk factors for chronic TMD, while another 6 SNPs were associated with intermediate phenotypes for TMD. One study identified a serotonergic pathway in which multiple SNPs influenced risk of chronic TMD. Two other studies investigating gene-environment interactions found that effects of stress on pain were modified by variation in the gene encoding catechol O-methyltransferase. Lessons learned from OPPERA have verified some implicated risk factors for TMD and refuted others, redirecting our thinking. Now it is time to apply those lessons to studies investigating treatment and prevention of TMD.

Symptom clustering in hospitalised older palliative cancer patients: A cross-sectional study

BACKGROUND

Accurate detection of symptoms is essential in palliative care. Identification of clustering of symptom is valuable to develop target interventions. This area is largely understudied in older palliative cancer patients.

OBJECTIVES

To identify symptom clustering in older palliative cancer patients, and patient groups based on the clustering of symptoms, and to evaluate the difference in functional dependence and experiencing life as not meaningful between the identified patient groups.

DESIGN

A cross-sectional study.

SETTING

Geriatric and non-geriatric wards of seven acute care hospitals.

PARTICIPANTS

400 palliative cancer patients aged 65 years and older.

METHODS

Symptoms were collected using a validated instrument which assesses physical, psychological, functional, social, and existential symptoms by means of a structured interview with a researcher. An agglomerative hierarchical clustering analysis was used to analyse the data.

RESULTS

The cluster analysis revealed five groups of symptoms: (1) urological and gastrointestinal symptoms, and their treatment complications, (2) psychological and existential symptoms, (3) pain, constipation, sleeplessness and airway problems, (4) functionality problems, and (5) fatigue-related symptoms. Three patient groups were identified: (1) symptom-free group, (2) physical discomfort group, and (3) physical and psychological discomfort group. In the last group, significant more patients had a geriatric risk profile and less of them received chemotherapy. Patients in this group were more often functionally dependent and experienced their life as not meaningful.

CONCLUSION

Five groups of symptoms were identified. Three patient groups were identified which reported different levels of functionality and experiencing life as meaningful. Healthcare professionals should be triggered to detect symptom clusters and be alert to the presence of the other symptoms in the cluster when identifying one symptom. They should also be alert to patients with a geriatric risk profile because of their higher risk of experiencing physical and psychological symptoms and the influence these symptoms have on being functionally dependent and experiencing life as not meaningful.

Correlates of self-report chronic insomnia disorders with 1-6 month and 6-month durations in home-dwelling urban older adults - the Shih-Pai Sleep Study in Taiwan: a cross-sectional community study

Background

To examine the correlates of insomnia disorder with different durations in home-dwelling older adults.

Methods

A cross-sectional survey in the Shih-Pai area of Taipei City, Taiwan (The Shih-Pai Sleep Study). A total 4047 subjects over the age of 65 years completed the study (2259 men and 1788 women). The Pittsburgh Sleep Quality Index and the duration of insomnia symptoms were used to identify DSM-IV 1–6 month and 6-month insomnia disorders.

Results

The prevalence of DSM-IV defined insomnia disorder was 5.8 %; two-thirds of these case lasted for ≥6 months. The shared correlates for both 1–6 and 6-month insomnia disorders were gender (women), depression and moderate pain. Pulmonary diseases were exclusively associated with 1–6 month insomnia disorder (OR: 2.57, 95 % CI: 1.46–4.52). In contrast, heart disease (OR: 1.73, 95 % CI: 1.21–2.49) and severe pain (OR: 2.34, 95 % CI: 1.14–4.40) were associated with 6-month insomnia disorder.

Conclusion

The prevalence of persistent insomnia disorder is higher than short-term insomnia disorder. Correlates for less persistent and more persistent insomnia disorder appears to be partially different. Duration quantifiers may be important in the identification of the etiology of insomnia and further studies with follow-ups are needed to examine the order of developing insomnia disorder and associated conditions.

Deconstructing Chronic Low Back Pain in the Older Adult-Step by Step Evidence and Expert-Based Recommendations for Evaluation and Treatment: Part VII: Insomnia

OBJECTIVE : To present the seventh in a series of articles designed to deconstruct chronic low back pain (CLBP) in older adults. This article focuses on insomnia and presents a treatment algorithm for managing insomnia in older adults, along with a representative clinical case. METHODS : A modified Delphi process was used to develop the algorithm and supportive materials. A multidisciplinary expert panel representing expertise in health psychology and sleep medicine developed the algorithm and supporting documents that were subsequently refined through an iterative process of input from a primary care provider panel. RESULTS : We present an illustrative clinical case and an algorithm to help guide the care of older adults with insomnia, an important contributor to CLBP and disability. Multicomponent cognitive behavioral therapy for insomnia (CBTI) and similar treatments (e.g., brief behavioral treatment for insomnia [BBTI]) are the recommended first-line treatment. Medications should be considered only if BBTI/CBTI is suboptimal or not effective and should be prescribed at the lowest effective dose for short periods of time (< 90 days). CONCLUSIONS : Insomnia is commonly comorbid with CLBP in older adults and should be routinely evaluated and treated because it is an important contributor to pain and disability. The algorithm presented was structured to assist primary care providers in planning treatment for older adults with CLBP and insomnia.

Improvements in Somatic Complaints Among Individuals With Serious Mental Illness Receiving Treatment in a Psychiatric Hospital

OBJECTIVE

Individuals with serious mental illness (SMI) experience significant comorbid somatic complaints. Little is known about response to integrated inpatient care that addresses psychiatric and general medical needs among individuals with SMI.

METHODS

Latent growth curve analyses were used to model somatic symptom trajectories across adult inpatients with SMI (n = 989). The Patient Health Questionnaire-15 (PHQ-15) was administered at admission, every 14 days, and at discharge.

RESULTS

Patients evidenced substantial reduction in somatization from admission (mean [standard deviation] = 9.0 [5.2]) to discharge (mean [standard deviation] = 5.2 [4.4]), with large effects (d = 0.83, 95% confidence interval = 0.76-0.90). Results indicate nonlinear improvement in somatic symptoms for 8 weeks of treatment, with greatest symptom reduction occurring during the first weeks of treatment with continued, albeit slowed, improvement until discharge. Initial PHQ-15 scores were lower among men and those who reported regular exercise in the 30 days preceding this hospitalization. In addition, presence of an anxiety disorder or personality disorder at admission; history of trauma, a gastrointestinal disorder, or major medical illness (within the past 3 months); and significant sleep disturbance independently contribute to higher PHQ-15 scores at admission. A substance use disorder and sleep disturbance were associated with greater immediate symptom reduction.

CONCLUSIONS

Somatic complaints can be managed in the context of inpatient psychiatric care integrated with 24-hour nursing and internal medicine specialists. Addressing psychiatric impairments, improving sleep, and ensuring abstinence from drugs and alcohol are associated with significant improvement in somatic complaints.

Insomnia in workers with delayed recovery from mild traumatic brain injury

OBJECTIVE/BACKGROUND/AIM

Insomnia has not been explored as it relates to recovery after mild traumatic brain injury (mTBI). We aimed to evaluate the prevalence of insomnia among Ontario workers with delayed recovery from mTBI, and its relationship with sociodemographic, TBI- and claim-related, behavioral, and clinical factors.

PATIENTS/METHODS

This was a cross-sectional study carried out over a period of 24 months in a large rehabilitation hospital in Ontario. To assess the prevalence of insomnia, we used the Insomnia Severity Index (ISI). Data were collected from standardized questionnaires, insurer records, and clinical assessment at the time of recruitment. Bivariate associations were calculated using the Spearman's correlation coefficient or analysis of variance. We established stepwise multivariate linear regression models of factors associated with insomnia. Additional analyses, including the assessment of the internal consistency of the ISI, were performed.

RESULTS

Of the 94 participants diagnosed with mTBI, clinical insomnia was reported by 69.2%. The mean age was 45.20 ± 9.94 years; 61.2% were men. No sex-related differences were observed in insomnia prevalence or severity. Insomnia was significantly associated with certain sociodemographic, claim-related, behavioral, and clinical variables. In the multivariable regression analysis, several determinants explained 53% of the insomnia variance. The internal consistency of the ISI, as measured by Cronbach's α, was 0.86.

CONCLUSIONS

Insomnia is common in persons with delayed recovery from mTBI, and is significantly associated with potentially modifiable clinical and nonclinical variables. Care of persons with brain injury requires greater attention with regard to the diagnosis and management of insomnia and associated disorders.

Subjective Sleep Quality Deteriorates Before Development of Painful Temporomandibular Disorder

There is good evidence that poor sleep quality increases risk of painful temporomandibular disorder (TMD). However, little is known about the course of sleep quality in the months preceding TMD onset, and whether the relationship is mediated by heightened sensitivity to pain. The Pittsburgh Sleep Quality Index was administered at enrollment into the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) prospective cohort study. Thereafter the Sleep Quality Numeric Rating Scale was administered every 3 months to 2,453 participants. Sensitivity to experimental pressure pain and pinprick pain stimuli was measured at baseline and repeated during follow-up of incident TMD cases (n = 220) and matched TMD-free controls (n = 193). Subjective sleep quality deteriorated progressively, but only in those who subsequently developed TMD. A Cox proportional hazards model showed that risk of TMD was greater among participants whose sleep quality worsened during follow-up (adjusted hazard ratio = 1.73, 95% confidence limits = 1.29, 2.32). This association was independent of baseline measures of sleep quality, psychological stress, somatic awareness, comorbid conditions, nonpain facial symptoms, and demographic characteristics. Poor baseline sleep quality was not significantly associated with baseline pain sensitivity or with subsequent change in pain sensitivity. Furthermore the relationship between sleep quality and TMD incidence was not mediated via baseline pain sensitivity or change in pain sensitivity.

PERSPECTIVE

Subjective sleep quality deteriorates progressively before the onset of painful TMD, but sensitivity to experimental pain does not mediate this relationship. Furthermore, the relationship is independent of potential confounders such as psychological stress, somatic awareness, comorbid conditions, nonpain facial symptoms, and various demographic factors.

An Evaluation of Central Sensitization in Patients With Sickle Cell Disease

Central sensitization (CS), nociceptive hyperexcitability known to amplify and maintain clinical pain, has been identified as a leading culprit responsible for maintaining pain in several chronic pain conditions. Recent evidence suggests that it may explain differences in the symptom experience of individuals with sickle cell disease (SCD). Quantitative sensory testing (QST) can be used to examine CS and identify individuals who may have a heightened CS profile. The present study categorized patients with SCD on the basis of QST responses into a high or low CS phenotype and compared these groups according to measures of clinical pain, vaso-occlusive crises, psychosocial factors, and sleep continuity. Eighty-three adult patients with SCD completed QST, questionnaires, and daily sleep and pain diaries over a 3-month period, weekly phone calls for 3 months, and monthly phone calls for 12 months. Patients were divided into CS groups (ie, no/low CS [n = 17] vs high CS [n = 21]), on the basis of thermal and mechanical temporal summation and aftersensations, which were norm-referenced to 47 healthy control subjects. High CS subjects reported more clinical pain, vaso-occlusive crises, catastrophizing, and negative mood, and poorer sleep continuity (Ps < .05) over the 18-month follow-up period. Future analyses should investigate whether psychosocial disturbances and sleep mediate the relationship between CS and pain outcomes.

PERSPECTIVE

In general, SCD patients with greater CS had more clinical pain, more crises, worse sleep, and more psychosocial disturbances compared with the low CS group.

Exploring the associations shared by mood, pain-related attention and pain outcomes related to sleep disturbance in a chronic pain sample

OBJECTIVE

Sleep disturbance in chronic pain is common, occurring in two-thirds of patients. There is a complex relationship between chronic pain and sleep; pain can disrupt sleep and poor sleep can exaggerate pain intensity. This may have an impact on both depressive symptoms and attention to pain. This study aims to evaluate the relationship between chronic pain and sleep, and the role of mood and attention.

METHODS

Chronic pain patients, recruited from a secondary care outpatient clinic, completed self-report measures of pain, sleep, depressive symptoms and attention to pain. Hierarchical regression and structural equation modelling were used to explore the relationships between these measures. Participants (n = 221) were aged between 20 and 84 (mean = 52) years.

RESULTS

The majority of participants were found to be 'poor sleepers' (86%) with increased pain severity, depressive symptoms and attention to pain. Both analytical approaches indicated that sleep disturbance is indirectly associated with increased pain severity Instead the relationship shared by sleep disturbance and pain severity was further associated with depressive symptoms and attention to pain.

CONCLUSIONS

Our results indicate that sleep disturbance may contribute to clinical pain severity indirectly though changes in mood and attention. Prospective studies exploring lagged associations between these constructs could have critical information relevant to the treatment of chronic pain.

The Unhappy Triad: Pain, Sleep Complaints, and Internalizing Symptoms

There is limited understanding of the etiology and temporal relations of chronic pain, sleep complaints, and depression/anxiety. Several models have been proposed by which sleep disruption represents a common mechanism for the comorbidity of these symptoms. The goals of this study were to 1) clarify the boundaries of these domains and to 2) examine the relations of these symptoms over time following exposure to stressful and potentially traumatic experiences during a combat deployment. We found support for three distinct domains of sleep complaints, internalizing symptoms, and physical complaints. We tested two competing models that have been proposed in the literature, controlling for negative and positive emotionality. Internalizing symptoms strongly mediated the relation between sleep complaints and pain (total effect = .15, direct effect = -.05). The study suggests that increases in sleep complaints immediately following deployment increase the risk of internalizing symptoms and pain several years after deployment.

The bidirectional relationship between sleep complaints and pain: Analysis of data from a randomized trial

OBJECTIVE

The goal of this study was to examine the bidirectional relationship of sleep and pain to determine whether changes in sleep complaints over the course of a chronic pain treatment trial predict pain outcomes and vice versa, controlling for changes in depression and anxiety.

METHODS

Data were analyzed from a 12-month randomized, controlled trial that tested the effectiveness of a collaborative care intervention for veterans with chronic musculoskeletal pain. Participants were 250 veterans from 5 primary care clinics in a Veteran Affairs (VA) medical center. Measures of pain, sleep, and depression/anxiety symptoms were collected at baseline, 3 months, and 12 months. Factor analysis was used to clarify the boundaries of these domains, and structural equation modeling was used to examine whether changes in sleep complaints and depression/anxiety during the trial predicted pain at the end of the trial, controlling for covariates. An alternative model was also tested in which changes in pain predicted sleep complaints.

RESULTS

Changes in sleep complaints at 3 months significantly predicted changes in pain at 12 months (standardized path coefficient = .29, p < .001). To a lesser extent, changes in pain predicted changes in sleep (standardized path coefficient = .15, p < .05). Changes in depression/anxiety did not significantly predict changes in pain or sleep. There was also evidence of differential relations of specific sleep complaints with pain.

CONCLUSIONS

This work helps to further disentangle the complex relationship between pain and sleep. This bidirectional relationship may need to be considered to improve pain outcomes.

Sleep Deprivation and Recovery Sleep Prior to a Noxious Inflammatory Insult Influence Characteristics and Duration of Pain

STUDY OBJECTIVES

Insufficient sleep and chronic pain are public health epidemics. Sleep loss worsens pain and predicts the development of chronic pain. Whether previous, acute sleep loss and recovery sleep determine pain levels and duration remains poorly understood. This study tested whether acute sleep deprivation and recovery sleep prior to formalin injection alter post-injection pain levels and duration.

METHODS

Male Sprague-Dawley rats (n = 48) underwent sleep deprivation or ad libitum sleep for 9 hours. Thereafter, rats received a subcutaneous injection of formalin or saline into a hind paw. In the recovery sleep group, rats were allowed 24 h between sleep deprivation and the injection of formalin. Mechanical and thermal nociception were assessed using the von Frey test and Hargreaves' method. Nociceptive measures were performed at 1, 3, 7, 10, 14, 17 and 21 days post-injection.

RESULTS

Formalin caused bilateral mechanical hypersensitivity (allodynia) that persisted for up to 21 days post-injection. Sleep deprivation significantly enhanced bilateral allodynia. There was a synergistic interaction when sleep deprivation preceded a formalin injection. Rats allowed a recovery sleep period prior to formalin injection developed allodynia only in the injected limb, with higher mechanical thresholds (less allodynia) and a shorter recovery period. There were no persistent changes in thermal nociception.

CONCLUSION

The data suggest that acute sleep loss preceding an inflammatory insult enhances pain and can contribute to chronic pain. The results encourage studies in a model of surgical pain to test whether enhancing sleep reduces pain levels and duration.

Psychometric Validation of the Insomnia Severity Index in Adults with Sickle Cell Disease

BACKGROUND

The Insomnia Severity Index (ISI) is an instrument to evaluate insomnia symptoms. The psychometric properties have not been established in adults (18 years of age or older) with sickle cell disease (SCD).

OBJECTIVE

Evaluate the reliability and validity of the ISI among adults with SCD.

METHODS

Analysis included psychometric evaluation with exploratory factor analysis.

RESULTS

Our 263 participants had a mean age of 35.6 years and primarily were female (54.8%) with HbSS genotype (69.2%). Almost 41% were classified as clinical insomnia cases (ISI ≥14) using the traditional scoring approach. Two factors, Insomnia Symptoms and Insomnia Impact, emerged during factor analysis. Reliability of both factor-scales was good and each correlated with pain severity and depressive symptomatology (r = 0.38 to 0.66, p<.01).

CONCLUSION

The ISI demonstrated construct validity and reliability for evaluating insomnia symptomatology among adults with SCD and can be used in research and clinical practice.

Patients with chronic pain: One-year follow-up of a multimodal rehabilitation programme at a pain clinic

BACKGROUND AND AIMS

Multimodal rehabilitation (MMR) programmes, including, physical training, educational and psychological interventions by an interdisciplinary team are found to be more successful for patients with disabling chronic pain compared with less comprehensive treatments. MMR programmes are based on the biopsychosocial model and the goal is usually to improve function, quality of life and facilitate and enable return to work. As pain clinics traditionally offer conventional medical pain treatment, there is limited knowledge about MMR given in this context. The aim of our study was to describe characteristics of patients with chronic pain, treated with a MMR programme at a conventional pain clinic, to evaluate patient-reported outcome measures (PROM) from start to one year after, and to study possibly associated factors for the improvement of health-related quality of life after one year.

METHODS

A prospective, observational study with a one-year follow-up was performed.

SUBJECTS

A total of 42 individuals (38 females, age 44.0±12.3 years and 4 men age 40±8.5 years) with different pain diagnoses were included. After a team assessment, the patients began a programme that lasted about three months. The MMR programme contained coordinated, individually adapted treatments administered individually or in groups, and was based on cognitive behavioural principles. Questionnaires regarding health-related quality of life (HRQoL) (EQ-5D), insomnia (ISI), mental health (HADS), pain-related disability (PDI), kinesiophobia (TSK), current pain intensity (VAS) and sense of coherence (SOC) were used at the start of the MMR and at follow-up. Demographic data were collected from the patient records.

RESULTS

The PROM at baseline showed substantial pain problems with low HRQoL (EQ-5D index of 0.1±0.282, and EQ VAS of 32.67±20.1), moderate insomnia (ISI 18.95±6.7), doubtful cases of depression and anxiety (HADS-depression 9.35±4.1 and HADS-anxiety 9.78±3.95), presence of pain-related disability (PDI 39.48 ±12.64), kinesiophobia (TSK 40.8±9.8), as well as moderate current pain (VAS 61.31±20.4). The sense of coherence was weak (SOC of 51.37±14). At one-year follow-up, significant (p≤0.05) improvement occurred on the EQ-5D index, EQ VAS, ISI, PDI and TSK. In the logistic regression analysis, no significant associations could be identified.

CONCLUSIONS

MMR for patients with complex pain problems can be a successful treatment alternative at conventional pain clinics.

IMPLICATIONS

Since access to rehabilitation clinics in Sweden may be limited, the availability of MMR can increase by providing this type of intervention in pain clinics. Increased knowledge of MMR in different settings can also contribute to increased understanding and collaboration between pain clinics and rehabilitation units.

Minority Aging and Endogenous Pain Facilitatory Processes

OBJECTIVE

The aim of the current study was to examine the relationships among age, ethnicity, and endogenous pain facilitation using temporal summation (TS) responses to mechanical and heat stimuli.

DESIGN

The present study assessed hyperalgesia and pain facilitation to thermal and mechanical stimuli at the knee and distal sites in 98 pain-free men and women. Participants were drawn from two ethnic groups [African-American (AA) and non-Hispanic white (NHW)] and two age groups (19-35 and 45-85).

RESULTS

Significant main effects of ethnicity were demonstrated for both mechanical and heat modalities (all P's ≤ 0.05), suggesting that AA participants, relative to NHW counterparts, demonstrated enhanced hyperalgesia. Age differences (older > younger) in hyperalgesia were found in mechanical pain ratings only. Results indicated that mechanical pain ratings significantly increased from first to maximal pain as a function of both age group and ethnicity (all P's ≤ 0.05), and a significant ethnicity by age interaction for TS of mechanical pain was found at the forearm (P < 0.05) and trended toward significance at the knee (P = 0.071). Post-hoc tests suggested that results were primarily driven by the older AA participants, who demonstrated the greatest mechanical TS. Additionally, evidence of differences in heat TS due to both ethnicity alone (all P's ≤ 0.05) and minority aging was also found.

CONCLUSIONS

This study provides evidence suggesting that older AAs demonstrate enhanced pain facilitatory processes, which is important because this group may be at increased risk for development of chronic pain. These results underscore the necessity of testing pain modulatory mechanisms when addressing questions related to pain perception and minority aging.