Unpacking the burden: understanding the relationships between chronic pain and comorbidity in the general population

Musculoskeletal sensitization and sleep: chronic muscle pain fragments sleep of mice without altering its duration

STUDY OBJECTIVES

Musculoskeletal pain in humans is often associated with poor sleep quality. We used a model in which mechanical hypersensitivity was induced by injection of acidified saline into muscle to study the impact of musculoskeletal sensitization on sleep of mice.

DESIGN

A one month pre-clinical study was designed to determine the impact of musculoskeletal sensitization on sleep of C57BL/6J mice.

METHODS

We instrumented mice with telemeters to record the electroencephalogram (EEG) and body temperature. We used an established model of musculoskeletal sensitization in which mechanical hypersensitivity was induced using two unilateral injections of acidified saline (pH 4.0). The injections were given into the gastrocnemius muscle and spaced five days apart. EEG and body temperature recordings started prior to injections (baseline) and continued for three weeks after musculoskeletal sensitization was induced by the second injection. Mechanical hypersensitivity was assessed using von Frey filaments at baseline (before any injections) and on days 1, 3, 7, 14, and 21 after the second injection.

RESULTS

Mice injected with acidified saline developed bilateral mechanical hypersensitivity at the hind paws as measured by von Frey testing and as compared to control mice and baseline data. Sleep during the light period was fragmented in experimental mice injected with acidified saline, and EEG spectra altered. Musculoskeletal sensitization did not alter the duration of time spent in wakefulness, non-rapid eye movement sleep, or rapid eye movement sleep.

CONCLUSIONS

Musculoskeletal sensitization in this model results in a distinct sleep phenotype in which sleep is fragmented during the light period, but the overall duration of sleep is not changed. This study suggests the consequences of musculoskeletal pain include sleep disruption, an observation that has been made in the clinical literature but has yet to be studied using preclinical models.

Impact of noncancer pain on health-related quality of life

BACKGROUND

While the economic costs of pain have been documented, the impact of noncancer pain on quality of life has not been studied extensively.

OBJECTIVE

To estimate the influence of noncancer pain on quality of life measures.

DESIGN

Prospective, multicenter, observational nonrandomized patient pain registry.

SETTING

Outpatient settings.

PARTICIPANTS

Patients with acute episodes of noncancer pain requiring treatment with a prescription medication containing oxycodone immediate-release on an as-needed basis for at least 5 days (n = 629).

MEASUREMENTS

The modified Brief Pain Inventory and the 12-item Short Form Health Survey (SF-12) was measured at baseline when oxycodone immediate-release began and days 7, 14, 21, and 28. Repeated measures mixed models provided estimates of impact of pain on the physical component summary score (PCS) and mental health component summary score (MCS) of the SF-12.

RESULTS

Patterns indicating pain oscillation over the 28-day window were common (Range: 44.3% back/neck pain cohort to 61.2% postoperative cohort). After adjustment for sociodemographics, concomitant medications and gastrointestinal symptoms, worst pain in 24 hours was associated with a 13.9 point PCS reduction (adjusted PCS for pain = 10: 31.1; adjusted PCS for pain = 0: 45.0) and a 7.2 point MCS reduction (adjusted MCS for pain = 10: 44.1; adjusted MCS for pain = 0: 51.3). Similar clinically relevant differences were observed among patients with arthritis, back/neck pain, injury/trauma, postoperative pain, neuropathic pain and fibromyalgia, although statistical significance was not observed in the latter 2 groups.

CONCLUSION

Among outpatients with various underlying causes of pain, the negative impact of pain on physical and mental health-related quality of life is significant.

Pain Symptoms in Fibromyalgia Patients with and without Provoked Vulvodynia

Objective. The aim of the study was to compare the pain symptoms of fibromyalgia patients exhibiting (FMS+PVD) and not exhibiting (FMS) comorbidity with provoked vulvodynia. Study Design. The case control study was performed in 39 patients who had been diagnosed with FMS and accepted to undergo gynaecological examination and in 36 healthy women (C). All patients completed standardized questionnaires for pain intensity, pain area, and psychological functioning. The gynaecological examination included vulvar pain pressure reactivity (Q-tip), pelvic tone assessment (Kegel manoeuver), and a semistructured interview collecting detailed information about pelvic symptoms and sexual function. Results. FMS+PVD patients displayed a higher number of associated symptoms than FMS patients. The vulvar excitability was significantly higher in FMS+PVD than in FMS and in both groups than in Controls. Half of FMS+PVD patients were positive to Kegel manoeuver and displayed higher scores in widespread pain intensity, STAI-Y2, and CESD levels than Kegel negative patients. Conclusions. The study reveals that increased vulvar pain excitability may occur in FMS patients independently of the presence of coital pain. Results suggest that coital pain develops in patients with higher FMS symptoms severity due to the cooperative effects of peripheral and central sensitization mechanisms.

Neurobiology of stress-induced hyperalgesia

The intensity and severity of perceived pain does not correlate consistently with the degree of peripheral or central nervous system tissue damage or with the intensity of primary afferent or spinal nociceptive neurone activity. In this respect, the modulation of pain by emotion and context is now widely recognized. In particular, stress, fear and anxiety exert potent, but complex, modulatory influences on pain. Stress can either suppress pain (stress-induced analgesia) or exacerbate it (stress-induced hyperalgesia; SIH) depending on the nature, duration and intensity of the stressor. Herein, we review the methods and models used to study the phenomenon of SIH in rodents and humans and then present a detailed discussion of our current understanding of neural substrates and neurobiological mechanisms. The review provides perspectives and challenges for the current and future treatment of pain and the co-morbidity of pain with stress-related psychiatric disorders including anxiety and depression.

Chronic pain epidemiology - where do lifestyle factors fit in?

Chronic pain is common and complex and has a large impact on individuals and society. Good epidemiological pain data provide key information on the use of resources (both in general practice and in specialist clinics), insight into factors that lead to or favour chronicity and the design of interventions aimed at reducing or preventing the effects of chronic pain. This review aims to highlight the important factors associated with chronic pain, including those factors which are amenable to lifestyle intervention.

Persistent post-surgical pain and experimental pain sensitivity in the Tromsø study: comorbid pain matters

In a large survey incorporating medical examination (N=12,981), information on chronic pain and surgery was collected, and sensitivity to different pain modalities was tested. Tolerance to the cold pressor test was analysed with survival statistics for 10,486 individuals, perceived cold pressor pain intensity was calculated for 10,367 individuals, heat pain threshold was assessed for 4,054 individuals, and pressure pain sensitivity for 4,689 individuals. Persistent post-surgical pain, defined by self-report, was associated with lower cold pressor tolerance (sex-adjusted hazard ratio=1.34, 95% confidence interval=1.08-1.66), but not when adjusting for other chronic pain. Other experimental pain modalities did not differentiate between individuals with or without post-surgical pain. Of the individuals with chronic pain (N=3352), 6.2% indicated surgery as a cause, although only 0.5% indicated surgery as the only cause. The associations found between persistent post-surgical pain and cold pressor tolerance is largely explained by the co-existence of chronic pain from other causes. We conclude that most cases of persistent post-surgical pain are coexistent with other chronic pain, and that, in an unselected post-surgical population, persistent post-surgical pain is not significantly associated with pain sensitivity when controlling for comorbid pain from other causes. A low prevalence of self-reported persistent pain from surgery attenuates statistically significant associations. We hypothesize that general chronic pain is associated with central changes in pain processing as expressed by reduced tolerance for the cold pressor test.

Chronic pain epidemiology and its clinical relevance

Chronic pain affects ∼20% of the European population and is commoner in women, older people, and with relative deprivation. Its management in the community remains generally unsatisfactory, partly because of lack of evidence for effective interventions. Epidemiological study of chronic pain, through an understanding of its distribution and determinants, can inform the development, targeting, and evaluation of interventions in the general population. This paper reviews current knowledge of risk markers associated with chronic pain and considers how these might inform management and prevention. Risk factors include socio-demographic, clinical, psychological, and biological factors. These are relevant to our understanding of chronic pain mechanisms and the nature of, and responses to, current and future treatments.

Tramadol/Paracetamol fixed-dose combination for chronic pain management in family practice: a clinical review

The family practitioner plays an important role in the prevention, diagnosis, and early management of chronic pain. He/she is generally the first to be consulted, the one most familiar with the patients and their medical history, and is likely the first to be alerted in case of inadequate pain control or safety and tolerability issues. The family practitioner should therefore be at the center of the multidisciplinary team involved in a patient's pain management. The most frequent indications associated with chronic pain in family practice are of musculoskeletal origin, and the pain is often multimechanistic. Fixed-dose combination analgesics combine compounds with different mechanisms of action; their broader analgesic spectrum and potentially synergistic analgesic efficacy and improved benefit/risk ratio might thus be useful. A pain specialist meeting held in November 2010 agreed that the fixed-dose combination tramadol/paracetamol might be a useful pharmacological option for chronic pain management in family practice. The combination is effective in a variety of pain conditions with generally good tolerability. Particularly in elderly patients, it might be considered as an alternative to conventional analgesics such as NSAIDs, which should be used rarely with caution in this population.

Brief, self-report fibromyalgia screener evaluated in a sample of chronic pain patients

OBJECTIVE

To validate a self-report fibromyalgia screener in a chronic pain population.

DESIGN

Adults with chronic pain were evaluated with a six-item, self-report fibromyalgia screening tool based on revised American College of Rheumatology (ACR) fibromyalgia diagnostic criteria, with fibromyalgia diagnosed when patients experienced chronic pain and scored ≥13 on the ACR fibromyalgia symptom severity scale. Patients were independently assigned clinical diagnoses by treating clinicians.

SETTING

University-based, tertiary care pain clinic.

SUBJECTS

Three hundred thirty-seven mixed chronic pain patients.

RESULTS

Agreement between the clinical diagnosis and screener diagnosis was good (P < 0.001), with 76% sensitivity and 82% specificity.

CONCLUSION

A self-administered, brief fibromyalgia screening questionnaire can effectively identify chronic pain patients who will likely have clinical fibromyalgia.

Self-management intervention for chronic pain in older adults: a randomised controlled trial

This study compared an outpatient pain self-management (PSM) program, using cognitive-behavioural therapy and exercises, with 2 control conditions in 141 chronic pain patients aged > 65 years. Results immediately posttreatment indicated that relative to the Exercise-Attention Control (EAC) group, the PSM group was significantly improved on measures of pain distress, disability, mood, unhelpful pain beliefs, and functional reach. The mean effect size for these gains was 0.52 (range: 0.44-0.68). By 1-month follow-up, relative to the EAC group, the PSM group remained better on most measures. At the 1-month follow-up, relative to a Waiting List (usual care) (WL) group, the PSM group was significantly improved on measures of pain distress, disability, and unhelpful pain beliefs. The mean effect size for these variables was 0.69 (range: 0.56-0.83). Relative to the WL group, the EAC group made no significant gains on any of the measured variables. At 1-month follow-up, the mean proportion of reliably improved cases (across outcome variables) was 41% (range: 16-60%) for the PSM group, twice that of those who met this criterion in the 2 control conditions (and this difference was statistically significant). Similarly, significantly more (44%) of the PSM group (vs 22% and 20% for the control groups) achieved a clinically significant improvement on pain disability. In the short term at least, cognitive-behavioural therapy-based PSM was more effective than exercises and usual care.

Epidemiology of pain among outpatients in methadone maintenance treatment programs

BACKGROUND

This analysis explored the prevalence and correlates of pain in patients enrolled in methadone maintenance treatment (MMT).

METHODS

Patients in two MMT programs starting a hepatitis care coordination randomized controlled trial completed the Brief Pain Inventory Short-Form and other questionnaires. Associations between clinically significant pain (average daily pain≥5 or mean pain interference≥5 during the past week) and sociodemographic data, medical status, depressive symptoms, and health-related quality of life, and current substance use were evaluated in multivariate analyses.

RESULTS

The 489 patients included 31.8% women; 30.3% Hispanics, 29.4% non-Hispanic Blacks, and 36.0% non-Hispanic Whites; 60.1% had hepatitis C, 10.6% had HIV, and 46.8% had moderate or severe depressive symptomatology. Mean methadone dose was 95.7mg (SD 48.9) and urine drug screening (UDS) was positive for opiates, cocaine, and amphetamines in 32.9%, 40.1%, and 2.9%, respectively. Overall, 237 (48.5%) reported clinically significant pain. Pain treatments included prescribed opioids (38.8%) and non-opioids (48.9%), and self-management approaches (60.8%), including prayer (33.8%), vitamins (29.5%), and distraction (12.7%). Pain was associated with higher methadone dose, more medical comorbidities, prescribed opioid therapy, and more severe depressive symptomatology; it was not associated with UDS or self-reported substance use.

CONCLUSIONS

Clinically significant pain was reported by almost half of the patients in MMT programs and was associated with medical and psychological comorbidity. Pain was often treated with opioids and was not associated with measures of drug use. Studies are needed to further clarify these associations and determine their importance for pain treatment strategies.

Construct and criterion-based validity of brief pain coping scales in persons with chronic knee osteoarthritis pain

OBJECTIVES

A recent trend in clinical practice is to adopt short screening and diagnostic self-report instruments for patients with chronic pain. Brief two-item pain coping and beliefs measures have recently been developed and have potential to improve decision making in clinical practice. Our study examined the construct and criterion-based validity of the two-item per scale version of the coping strategies questionnaire (CSQ).

DESIGN

We used data obtained on a community-based sample of 873 persons with chronic knee osteoarthritis pain from the Osteoarthritis Initiative, a large longitudinal cohort study. Persons were administered the two-item per scale version of the CSQ. The International Classification of Functioning framework was used to select a variety of criterion-based measures for comparison with the CSQ. Spearman correlations and hierarchical regression models were used to characterize construct validity and receiver operating characteristic (ROC) curves, sensitivity and specificity were used to describe criterion-based validity.

RESULTS

Construct validity of the CSQ scales was generally supported, with the Catastrophizing and Praying or Hoping scales demonstrating the strongest construct validity across criterion measures. Criterion-based validity for the CSQ scales varied depending on the criterion measure. The Catastrophizing and Praying or Hoping scales also had the strongest criterion-based validity, with ROC curve areas as high as 0.71 (95% confidence interval = 0.67, 0.75), P < 0.001, for identifying persons with substantial physical function deficits.

CONCLUSIONS

The findings suggest that several of the two-item CSQ scales demonstrate a modest level of construct validity along with fair criterion-based validity. The Catastrophizing and Praying or Hoping scales appear to hold the most promise for clinical applications and future longitudinal research.

Exploring the Causes of Neck Pain and Disability as Perceived by Those Who Experience the Condition: A Mixed-Methods Study

Designing effective treatment protocols for neck-related disability has proven difficult. Disability has been examined from structural, emotional, and cognitive perspectives, with evidence supporting a multidimensional nature. The patient’s perspective of their condition has found increasing value for patient-centred, evidence-informed care. This cross-sectional study utilized descriptive thematic analysis to examine perceptions of causation in 118 people with neck pain. The Brief Illness Perceptions Questionnaire was used to capture perceptions of causation for neck pain symptoms. The Neck Disability Index, the Pain Catastrophizing Scale, the Hospital Anxiety and Depression Scale, and the P4 pain intensity numeric rating scale were also collected. Eight main themes were found for the cause(s) of neck pain: posture and movement, structure and mechanism, emotions, predisposition and lifestyle, symptoms, fatigue and insomnia, treatment, and environment. A series of regression models stratified by perceived cause suggested that disability could be explained by different constructs across the larger of the main themes. The findings are discussed in terms of the false view that mechanical neck pain should be considered a homogenous condition and potential application to treatment decision making based on patient perspectives.

Twin studies of pain

Twin studies provide a method for estimating the heritability of phenotypes and for examining genetic and environmental relationships between phenotypes. We conducted a systematic review of twin studies of pain, including both clinical and experimental pain phenotypes. Fifty-six papers were included, whereof 52 addressed clinical phenotypes. Of the most comprehensively studied phenotypes, available data indicates heritability around 50% for migraine, tension-type headache and chronic widespread pain, around 35% for back and neck pain, and around 25% for irritable bowel syndrome. However, differences in phenotype definitions make these results somewhat uncertain. All clinical studies relied on dichotomous outcomes and none used pain intensity as continuous phenotype. This is a major weakness of the reviewed studies and gives reason to question their validity with respect to pain mechanisms. Experimental pain studies indicate large differences in heritability across pain modalities. Whereas there is evidence for substantial common genetic risk across many clinical pain conditions, different experimental pain phenotypes appear to be associated with different genetic factors. Recommendations for future research include inclusion of pain intensity scaling and number of pain sites in phenotyping. Furthermore, studies examining the genetic relationships between pain phenotypes, in particular between clinical and experimental phenotypes, should be prioritized.