The journal of pain : official journal of the American Pain Society
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Experimental pain research frequently relies on the recruitment of volunteers. However, because experimental pain research often involves unpleasant and painful sensations, it may be especially susceptible to sampling bias. That is, volunteers in experimental pain research might differ from nonvolunteers on several relevant variables that could affect the generalizability and external validity of the research. ⋯ Study 1 showed that lower levels of fear of pain, higher levels of sensation-seeking, and older age predicted the perceived likelihood of participating in pain research. Study 2 showed significantly higher levels of sensation-seeking in participants who signed up for the pain study compared with those who signed up for the no-pain study. The implications of these findings for future research, as well as the clinical conclusions on the basis of experimental pain research, are discussed.
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Pain after spinal cord injury (SCI-Pain) is one of the most debilitating sequelae of spinal cord injury, characterized as relentless, excruciating pain that is largely refractory to treatments. Although it is generally agreed that SCI-Pain results from maladaptive plasticity in the pain processing pathway that includes the spinothalamic tract and somatosensory thalamus, the specific mechanisms underlying the development and maintenance of such pain are yet unclear. However, accumulating evidence suggests that SCI-Pain may be causally related to abnormal thalamic disinhibition, leading to hyperactivity in the posterior thalamic nucleus (PO), a higher-order nucleus involved in somatosensory and pain processing. ⋯ The substantial tonic activation of presynaptic GABAB receptors on GABAergic projections to PO-characteristic of normal animals-was absent in mice with SCI-Pain. Also absent in mice with SCI-Pain was the normal presynaptic regulation of glutamatergic projections to the PO by GABAB receptors. The loss of these regulatory presynaptic mechanisms in SCI-Pain may be an element of maladaptive plasticity leading to PO hyperexcitability and behavioral pain, and may suggest targets for development of novel treatments.
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Fibromyalgia (FM) is a condition with chronic widespread pain and signs of generalized pain hypersensitivity. FM has previously been classified according to the American College of Rheumatology-1990 criteria, where the presence of hypersensitivity is estimated by a tender point examination. Because of the limitations of these classification criteria, new diagnostic criteria have been proposed, abandoning this examination. ⋯ Patients fulfilling the FM criteria (n = 498, 37%) reported significantly higher levels of pain, pain-related disability, psychological distress, and sensitivity to mechanical and heat stimuli (P < .05). Moreover, the proportion using opioids were significantly higher compared with patients not fulfilling the criteria (P = .015). Significant associations were found between heat and mechanical pain sensitivity (P < .001) indicating that patients who showed higher pain sensitivity to mechanical stimulation also showed higher pain sensitivity to thermal stimulation.
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Multicenter Study
Within-Person Pain Variability and Mental Health in Older Adults With Osteoarthritis: An Analysis Across 6 European Cohorts.
Pain is a key symptom of osteoarthritis (OA) and has been linked to poor mental health. Pain fluctuates over time within individuals, but a paucity of studies have considered day-to-day fluctuations of joint pain in relation to affective symptoms in older persons with OA. This study investigated the relationship of pain severity as well as within-person pain variability with anxiety and depression symptoms in 832 older adults with OA who participated in the European Project on OSteoArthritis (EPOSA): a 6-country cohort study. ⋯ Moreover, older-old participants experienced fewer symptoms of anxiety (ratio = .85, 95% confidence interval [CI], .77-.94), depression (ratio = .90, 95% CI, .82-.98), and total affective symptoms (ratio = .87, 95% CI, .79-.94) if their pain fluctuated more. No such association was evident in younger-old participants (65-74.0 years). These findings imply that stable pain levels are more detrimental to mental health than fluctuating pain levels in older persons.
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Conditioned pain modulation (CPM), a psychophysical paradigm that is commonly used to infer the integrity of endogenous pain-altering systems by observation of the effect of one noxious stimulus on another, has previously identified deficient endogenous analgesia in fibromyalgia (FM) and other chronic pain conditions. The mechanisms underlying this deficiency, be they insufficient inhibition and/or active facilitation, are largely unknown. ⋯ Higher resting connectivity between this cluster and cortical pain processing regions was associated with more efficient inhibitory CPM in both groups, whereas PAG connectivity with the dorsal pons was associated with greater CPM inhibition only in HC. Greater PAG connectivity to the caudal pons/rostral medulla, which was pain-inhibitory in HC, was associated with pain facilitation in FM patients.