The journal of pain : official journal of the American Pain Society
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The presence of bimodal outcome distributions has been used as a justification for conducting responder analyses, in addition to, or in place of analyses of the mean between-group difference, in clinical trials and systematic reviews of interventions for pain. The aim of this study was to investigate the distribution of participants' pain outcomes for evidence of bimodal distribution. We sourced data on participant outcomes from a convenience sample of 10 trials of nonsurgical interventions (exercise, manual therapy, medication) for spinal pain. ⋯ We found no compelling evidence suggesting that outcomes were bimodally distributed for any of the intervention groups. Responder analysis would not meaningfully alter our interpretation of these data compared with the mean between group difference. Our findings suggest that bimodal distribution of outcomes should not be assumed in interventions for spinal pain and do not support the automatic prioritization of responder analysis over the between group difference in the evaluation of treatment effectiveness for pain.
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Prominent clinical models of chronic pain propose a fundamental role of classical conditioning in the development of pain-related disability. If classical conditioning is key to this process, then people with chronic pain may show a different response to pain-related conditioned stimuli than healthy control subjects. We set out to determine whether this is the case by undertaking a comprehensive and systematic review of the literature. To identify studies comparing classical conditioning between people with chronic pain and healthy control subjects, the databases MEDLINE, PsychINFO, PsychARTICLES, Scopus, and CINAHL were searched using key words and medical subject headings consistent with 'classical conditioning' and 'pain.' Articles were included when: 1) pain-free control and chronic pain groups were included, and 2) a differential classical conditioning design was used. The systematic search revealed 7 studies investigating differences in classical conditioning between people with chronic pain and healthy control participants. The included studies involved a total of 129 people with chronic pain (fibromyalgia syndrome, spinal pain, hand pain, irritable bowel syndrome), and 104 healthy control participants. Outcomes included indices of pain-related conditioning such as unconditioned stimulus (US) expectancy and contingency awareness, self-report and physiological measures of pain-related fear, evaluative judgements of conditioned stimulus pleasantness, and muscular and cortical responses. Because of variability in outcomes, meta-analyses included a maximum of 4 studies. People with chronic pain tended to show reduced differential learning and flatter generalization gradients with respect to US expectancy and fear-potentiated eyeblink startle responses. Some studies showed a propensity for greater muscular responses and perceptions of unpleasantness in response to pain-associated cues, relative to control cues. ⋯ The review revealed preliminary evidence that people with chronic pain may exhibit less differential US expectancy and fear learning. This characteristic may contribute to widespread fear-avoidance behavior. The assumption that altered classical conditioning may be a predisposing or maintaining factor for chronic pain remains to be verified.
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Prominent clinical models of chronic pain propose a fundamental role of classical conditioning in the development of pain-related disability. If classical conditioning is key to this process, then people with chronic pain may show a different response to pain-related conditioned stimuli than healthy control subjects. We set out to determine whether this is the case by undertaking a comprehensive and systematic review of the literature. To identify studies comparing classical conditioning between people with chronic pain and healthy control subjects, the databases MEDLINE, PsychINFO, PsychARTICLES, Scopus, and CINAHL were searched using key words and medical subject headings consistent with 'classical conditioning' and 'pain.' Articles were included when: 1) pain-free control and chronic pain groups were included, and 2) a differential classical conditioning design was used. The systematic search revealed 7 studies investigating differences in classical conditioning between people with chronic pain and healthy control participants. The included studies involved a total of 129 people with chronic pain (fibromyalgia syndrome, spinal pain, hand pain, irritable bowel syndrome), and 104 healthy control participants. Outcomes included indices of pain-related conditioning such as unconditioned stimulus (US) expectancy and contingency awareness, self-report and physiological measures of pain-related fear, evaluative judgements of conditioned stimulus pleasantness, and muscular and cortical responses. Because of variability in outcomes, meta-analyses included a maximum of 4 studies. People with chronic pain tended to show reduced differential learning and flatter generalization gradients with respect to US expectancy and fear-potentiated eyeblink startle responses. Some studies showed a propensity for greater muscular responses and perceptions of unpleasantness in response to pain-associated cues, relative to control cues. ⋯ The review revealed preliminary evidence that people with chronic pain may exhibit less differential US expectancy and fear learning. This characteristic may contribute to widespread fear-avoidance behavior. The assumption that altered classical conditioning may be a predisposing or maintaining factor for chronic pain remains to be verified.