Epidemiology of chronic pain, from the laboratory to the bus stop: time to add understanding of biological mechanisms to the study of risk factors in population-based research?

Development of temporomandibular disorders is associated with greater bodily pain experience

OBJECTIVES

The aim of this study is to examine the difference in the report of bodily pain experienced by patients who develop temporomandibular disorders (TMD) and by those who do not develop TMD over a 3-year observation period.

METHODS

This is a 3-year prospective study of 266 females aged 18 to 34 years initially free of TMD pain. All patients completed the Symptom Report Questionnaire (SRQ) at baseline and yearly intervals, and at the time they developed TMD (if applicable). The SRQ is a self-report instrument evaluating the extent and location of pain experienced in the earlier 6 months. Statistical analysis was carried out using repeated measures ANOVA.

RESULTS

Over the 3-year period, 16 patients developed TMD based on the Research Diagnostic Criteria for TMD. Participants who developed TMD reported more headaches (P=0.0089), muscle soreness or pain (P=0.005), joint soreness or pain (P=0.0012), back pain (P=0.0001), chest pain (P=0.0004), abdominal pain (P=0.0021), and menstrual pain (P=0.0036) than Participants who did not develop TMD at both the baseline and final visits. Participants who developed TMD also reported significantly more headache (P=0.0006), muscle soreness or pain (P=0.0059), and other pains (P=0.0188) when they were diagnosed with TMD compared with the baseline visit.

DISCUSSION

The development of TMD was accompanied by increases in headaches, muscle soreness or pain, and other pains that were not observed in the Participants who did not develop TMD. Participants who developed TMD also report higher experience of joint, back, chest, and menstrual pain at baseline.

Extending conceptual frameworks: life course epidemiology for the study of back pain

BACKGROUND

Epidemiological studies have identified important causal and prognostic factors for back pain, but these frequently only identify a proportion of the variance, and new factors add little to these models. Recently, interest has increased in studying diseases over the life course, stimulated by the 1997 book by Kuh and Ben-Shlomo, a move accompanied by important conceptual and methodological developments. This has resulted in improvements in the understanding of other conditions like cardiovascular and respiratory disease. This paper aims to examine how conceptual frameworks from life course epidemiology could enhance back pain research.

DISCUSSION

Life course concepts can be divided into three categories. Concept 1: patterns over time, risk chains and accumulation. Simple 'chains of risk' have been studied - e.g. depression leading to back pain - but studies involving more risk factors in the chain are infrequent. Also, we have not examined how risk accumulation influences outcome, e.g. whether multiple episodes or duration of depression, throughout the life course, better predicts back pain. One-year back pain trajectories have been described, and show advantages for studying back pain, but there are few descriptions of longer-term patterns with associated transitions and turning points. Concept 2: influences and determinants of pathways. Analyses in back pain studies commonly adjust associations for potential confounders, but specific analysis of factors modifying risk, or related to the resilience or susceptibility to back pain, are rarely studied. Concept 3: timing of risk. Studies of critical or sensitive periods - crucial times of life which influence health later in life - are scarce in back pain research. Such analyses could help identify factors that influence the experience of pain throughout the life course.

SUMMARY

Back pain researchers could usefully develop hypotheses and models of how risks from different stages of life might interact and influence the onset, persistence and prognosis of back pain throughout the life course. Adoption of concepts and methods from life course epidemiology could facilitate this.

Pain associated with specific anxiety and depressive disorders in a nationally representative population sample

OBJECTIVE

To examine in a nationally representative sample (a) the differential association of specific anxiety and depressive disorders defined according to DSM-IV with pain disorder (PD) and pain symptoms, and (b) whether pain-associated anxiety and depressive disorders and their comorbidity have different implications in terms of impairment, disability, health care utilization, and substance use.

METHOD

A nationally representative community study was conducted in Germany. Symptoms, syndromes and diagnoses of mental disorders, and pain were assessed in N = 4,181 participants aged 18-65 years using the DSM-IV/M-CIDI.

RESULTS

Logistic regressions revealed that pain is associated with both specific anxiety and depressive disorders, with increasing significant odds ratios (OR) for medically explained pain symptoms (EPS; OR range: 1.9-2.0), to unexplained pain symptoms (UPS; OR range: 2.4-7.3), to PD (OR range: 3.3-14.8). PD and UPS persistently showed associations after adjusting for comorbid other anxiety and depressive disorders and physical illnesses. All types of pain, particularly PD/UPS, are associated with decreased quality of life, greater impairment in role functioning, disability, health care utilization, and substance use. Depressive disorders, even more so anxiety disorders and their comorbidity account for a substantial proportion of variance in these functional correlates.

CONCLUSIONS

Pain is strongly associated with specific anxiety and depressive disorders. In light of the individual and societal burden due to pain, and the demonstrated role of comorbid anxiety or/and depression, our results call for further investigation of the underlying mechanisms for this association as well as targeted treatments for these comorbidities.

A Cluster Within the Continuum of Biopsychosocial Distress Can Be Labeled “Fibromyalgia Syndrome” — Evidence from a Representative German Population Survey

Objective.

We tested the hypothesis that “fibromyalgia syndrome” is a biopsychosocial continuum disorder.

Methods.

A cross-sectional survey of a representative sample of the German general population with persons ≥ 14 years of age was conducted based on face-to-face contacts. Physical distress was measured by the regional pain scale (RPS) and the Patient Health Questionnaire 15 (PHQ-15), psychological distress by the PHQ-9, and social distress by the Oslo Social Support Scale. Health-related quality of life (HRQOL) was measured by the 12-item form of the Medical Outcome Study Short Form Health Survey. A k-means clustering procedure with 2–8 clusters preset was used to classify the scores of the RPS, PHQ-9, and PHQ-15. The number of clusters retained was based on the stability and interpretability of the clusters. The cluster analysis was first performed with a randomly selected half of the sample and then cross-validated on the second half of the total sample.

Results.

A 4-cluster solution produced the most stable and meaningful results. Cluster 1 was very low on all symptom scores. Cluster 2 was low on pain sites, somatic symptoms, and depression. Cluster 3 was high on pain scores, moderate on somatic symptoms, and low on depression. Cluster 4 was high on all symptom scores. The centroids of cluster 4 met the survey criteria of fibromyalgia syndrome. Cluster 4 reported a lower HRQOL and less social support compared to the other 3 groups.

Conclusion.

A cluster within the continuum of biopsychosocial distress can be labeled fibromyalgia syndrome.

Association between generalized anxiety levels and pain in a community sample: evidence for diagnostic specificity

BACKGROUND

It is unclear whether generalized anxiety disorder (GAD) has a specific relationship to pain syndromes, going beyond the established association of pain with anxiety syndromes in general.

METHODS

Mental disorders were assessed in a community sample (N=4181; 18-65 years) using the DSM-IV/M-CIDI. Several threshold definitions were used to define GAD and medically unexplained pain.

RESULTS

The association between pain and GAD (odds ratio, OR=5.8 pain symptoms; OR=16.0 pain disorder) is stronger than the association between pain and other anxiety disorders (OR=2.4 pain symptoms; OR=4.0 pain disorder). This association extends to subthreshold level definitions of GAD with some indication for a non-linear dose-response relationship. The GAD-pain link cannot sufficiently be explained by demographic factors, comorbid mental or physical disorders.

CONCLUSIONS

The association of pain and generalized anxiety is not artifactual. Compared to other anxiety syndromes, it appears to be stronger and more specific suggesting the need to explore clinical and public health implications.

Vitamin D and chronic widespread pain in a white middle-aged British population: evidence from a cross-sectional population survey

BACKGROUND

Identified aetiological factors for chronic widespread pain (CWP) are largely related to emotional and behavioural factors, but current management leads to modest improvement in symptoms. Vitamin D deficiency has been suggested as a new modifiable risk factor for CWP.

OBJECTIVE

To examine the association between vitamin D status (measured by 25-hydroxyvitamin D (25(OH)D)) and CWP in a nationwide population sample of white British adults, accounting for potential mediating and confounding lifestyle factors.

METHODS

9377 participants born 1 week in March 1958, in England, Scotland or Wales and completing a biomedical assessment at age 45; 6824 eligible participants had data on 25(OH)D and completed pain manikins.

RESULTS

Prevalence of CWP varied by 25(OH)D concentration in women but not in men, with the lowest prevalence observed for women with 75-99 nmol/l (14.4% for <25 nmol/l, 14.8% for 25-49 nmol/l, 11.6% for 50-74 nmo/l, 8.2% for 75-99 nmol/l and 9.8% for participants with > or =100 nmol/l). There was an interaction between 25(OH)D concentration and gender in relation to CWP (interaction, p = 0.006), which was not fully explained by differences in lifestyle or social factors (adjusted interaction, p = 0.03). For women, the association between 25(OH)D concentration and CWP persisted after full adjustment (odds ratio (OR) for <75 nmol/l vs 75-99 nmol/l 1.57, 95% CI 1.09 to 2.26), while no evidence for an association was apparent in men (OR = 1.03, 95% CI 0.75 to 1.43).

CONCLUSION

Current vitamin D status was associated with CWP in women but not in men. Follow-up studies are needed to evaluate whether higher vitamin D intake might have beneficial effects on the risk of CWP.

Progress in genetic studies of pain and analgesia

Interindividual variability in pain sensitivity and the response to analgesic manipulations remains a considerable clinical challenge as well as an area of intense scientific investigation. Techniques in this field have matured rapidly so that much relevant data have emerged only in the past few years. Our increasing understanding of the genetic mediation of these biological phenomena have nonetheless revealed their surprising complexity. This review provides a comprehensive picture and critical analysis of the field and its prospects.

Development of chronic pain following severe accidental injury. Results of a 3-year follow-up study

OBJECTIVE

Motor vehicle accidents (MVA) and work-related injuries are two of the more common causes of chronic pain. Nevertheless, there is little evidence on predicting factors regarding the development of chronic pain following physical injury.

METHODS

The present study investigated temporal associations between accident-related factors, psychological factors [symptoms of posttraumatic stress disorder (PTSD), anxiety, depression, coping], and the development of chronic pain in a sample of individuals who had sustained severe accidental injuries (N=90). Assessments were performed within 1 month of the accident, and at 6, 12, and 36 months post trauma.

RESULTS

A total of 40 individuals (44%) reported accident-related pain 3 years after the accident. Individuals with chronic pain showed significantly more symptoms of PTSD, depression, and anxiety, more disability, and more days off work. Analysis of temporal associations between psychological variables and the development of chronic pain indicated that the separation of the pain from the nonpain group mostly occurred between 6 (T2) and 12 months (T3). Differences were much less pronounced at T1.

CONCLUSION

The prevalence of chronic pain in severely injured patients 3 years after the accident is considerably high. The development of chronic pain is more related to psychological factors, particularly PTSD symptoms, in the aftermath of the accident, as compared to sociodemographic and accident-related variables at the time of the accident. These findings may be helpful to elucidate the problems in predicting chronic pain conditions in injured subjects and to recognize the onset of a chronic pain condition more reliably.

Regional pain syndrome: clinical characteristics, mechanisms and management

Regional soft-tissue complaints are commonplace, and they usually relate to a disease process, such as strain, inflammation or degeneration of a muscle, tendon or related muscle-tendon unit. The clinical features and investigations of the causative processes of these complaints are characteristic, and outcomes to treatments are usually predictable and satisfactory. Regional pain syndromes are different: these syndromes present with regional pain and tenderness, and other sensory symptoms unaccounted for by a simple musculoskeletal mechanistic explanation. Approved classification criteria for regional pain syndromes are lacking, and these syndromes are poorly understood and frequently misdiagnosed. Regional pain syndromes often occur after injury and overlap extensively with other musculoskeletal pain syndromes, in terms of clinical signs and symptoms. The clinician and patient are often confused about the nature of the problem and routine treatments directed to putative tissue damage will fail. Review of the epidemiology of regional pain syndromes combined with knowledge of other similar pain syndromes has enabled an evolving understanding of the condition. The musculoskeletal and central nervous systems both contribute to regional pain syndromes, through spine-related pain mechanisms and central sensitization, respectively. The patient's emotional state, particularly the effect on pain modulation, links these two systems.