The journal of pain : official journal of the American Pain Society
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Contingency learning, in particular the formation of danger beliefs, underpins conditioned fear and avoidance behavior, yet equally important is the formation of safety beliefs. That is, when threat beliefs and accompanying fear/avoidance spread to technically safe cues, it might cause disability. Indeed, such over generalization has been advanced as a trans-diagnostic pathologic marker, but it has not been investigated in chronic pain. Using a novel hand pain scenario contingency learning task, we tested the hypotheses that chronic hand pain patients demonstrate less differential pain expectancy judgments because of poor safety learning and demonstrate broader generalization gradients than healthy controls. Participants viewed digitized 3-dimensional hands in different postures presented in random order (conditioned stimulus [CS]) and rated the likelihood that a fictive patient would feel pain when moving the hand into that posture. Subsequently, the outcome (pain/no pain) was presented on the screen. One hand posture was followed by pain (CS+), another was not (CS-). Generalization was tested using novel hand postures (generalization stimuli) that varied in how similar they were to the original conditioned stimuli. Patients, but not healthy controls, demonstrated a contingency learning deficit determined by impaired safety learning, but not by exaggerated pain expectancy toward the CS+. Patients showed flatter, asymmetric generalization gradients than the healthy controls did, with higher pain expectancy for novel postures that were more similar to the original CS-. The results clearly uphold our hypotheses and suggest that contingency learning deficits might be important in the development and maintenance of the chronic pain-related disability. ⋯ Chronic hand pain patients demonstrate 1) reduced differential contingency learning determined by a lack of safety belief formation, but not by exaggerated threat belief formation, and 2) flatter, asymmetric generalization gradients than the healthy controls.
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Published adult prevalence estimates of chronic pain in the United States vary significantly. A more consistent pain measure is needed to assess unmet need for pain management in the general population. In this study, secondary analyses of the 2010 Quality of Life Supplement of the National Health Interview Survey are used to calculate the point prevalence of "persistent pain," which we defined as constant or frequent pain persisting for at least 3 months. Rates of persistent pain are also calculated by risk group, chronic condition, and disability status. Findings show that about 19.0% of adults in the United States report persistent pain. Rates of persistent pain are higher among women, adults aged 60 to 69, adults who rate their health as fair or poor, adults who are overweight or obese, and those who were hospitalized 1 or more times in the preceding year. Most adults who report conditions such as arthritis, carpal tunnel syndrome, or back or joint pain do not describe their pain as "persistent." Of the estimated 39.4 million adults who report persistent pain, 67.2% say their pain is "constantly present," and 50.5% say their pain is sometimes "unbearable and excruciating." ⋯ Persistent pain, defined as self-reported pain "every day" or "most days" in the preceding 3 months, is a useful way to characterize health-related quality of life in the general population, and policy makers should consider including this core measure in ongoing health surveys like the National Health Interview Survey and the Medical Expenditure Panel Survey, the authors conclude.
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Widespread hyperalgesia is well documented among adult patients with irritable bowel syndrome (IBS), but little is known about pain sensitivity among adolescents with IBS. We examined pain sensitivity in 961 adolescents from the general population (mean age 16.1 years), including pain threshold and tolerance measurements of heat (forearm) and pressure pain (fingernail and shoulder) and cold pressor tolerance (hand). Adolescents with IBS symptoms (Rome III criteria) had lower heat pain thresholds compared to controls after adjustments for sex, comorbid pain, and psychological distress (mean difference = -.8 °C; 95% confidence interval [CI] = -1.6 to -.04). Similar results were found for pressure pain threshold at the shoulder (mean difference = -46 kPa; 95% CI = -78 to -13) and fingernail (mean difference = -62 kPa; 95% CI = -109 to -15), and for an aggregate of all 3 threshold measures (z-score difference = -.4; 95% CI = -.6 to -.2), though pressure pain threshold differences were nonsignificant after the final adjustments for psychological distress. No difference of pain tolerance was found between the IBS cases and controls. Our results indicate that adolescents in the general population with IBS symptoms, like adults, have widespread hyperalgesia. ⋯ This is the first report of widespread hyperalgesia among adolescents with IBS symptoms in the general population, with lower pain thresholds found to be independent of sex and comorbid pain. Our results suggest that central pain sensitization mechanisms in IBS may contribute to triggering and maintaining chronic pain symptoms.
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Most studies on pain focus on specific disorders, which makes it difficult to compare characteristics across different types of pain symptoms. In this large population-based study, we examine the prevalence and comorbidity patterns among pain symptoms across a wide range of anatomic sites (back, neck, head, abdomen, joints, chest, face, teeth, and "other") in relation to anxious depression and a range of demographic, health, and lifestyle variables. Self-report data were collected in 11,787 adult participants of The Netherlands Twin Registry (mean age 44.5 years, 62% female), including twins and relatives of twins. Headache and abdominal pain were strongly associated with female sex, whereas chest pain and toothache were not. Joint pain strongly increased with age, whereas headache and abdominal pain decreased with age. Most other pain sites were only weakly associated with age. A highly consistent pattern of comorbidity was observed: All pain symptoms were correlated with all other pain symptoms, as well as with anxious depression. Frequent and widespread pain (ie, pain at multiple sites) was most strongly associated with anxious depression. These observations reflect important differences between specific pain symptoms, suggesting partly separate etiologies, but also highlight the importance of shared mechanisms underlying pain symptoms in general. ⋯ The association of pain with sex and age strongly depends on pain location. However, all pain sites are consistently associated with other pain sites as well as with anxious depression. This provides important clues with respect to both similarities and differences in the mechanisms underlying different types of pain.
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Temporomandibular disorder and irritable bowel syndrome are comorbid functional chronic pain disorders of unknown etiology that are triggered/exacerbated by stress. Here we present baseline phenotypic characterization of a novel animal model to gain insight into the underlying mechanisms that contribute to such comorbid pain conditions. In this model, chronic visceral hypersensitivity, a defining symptom of irritable bowel syndrome, is dependent on 3 factors: estradiol, existing chronic somatic pain, and stress. In ovariectomized rats, estradiol replacement followed by craniofacial muscle injury and stress induced visceral hypersensitivity that persisted for months. Omission of any 1 factor resulted in a transient (1 week) visceral hypersensitivity from stress alone or no hypersensitivity (no inflammation or estradiol). Maintenance of visceral hypersensitivity was estradiol dependent, resolving when estradiol replacement ceased. Referred cutaneous hypersensitivity was concurrent with visceral hypersensitivity. Increased spinal Fos expression suggests induction of central sensitization. These data demonstrate the development and maintenance of visceral hypersensitivity in estradiol-replaced animals following distal somatic injury and stress that mimics some characteristics reported in patients with temporomandibular disorder and comorbid irritable bowel syndrome. This new animal model is a powerful experimental tool that can be employed to gain further mechanistic insight into overlapping pain conditions. ⋯ The majority of patients with temporomandibular disorder report symptoms consistent with irritable bowel syndrome. Stress and female prevalence are common to both conditions. In a new experimental paradigm in ovariectomized rats with estradiol replacement, masseter inflammation followed by stress induces visceral hypersensitivity that persists for months, modeling these comorbid pain conditions.