Pain
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Randomized Controlled Trial
Individuals with chronic pain have the same response to placebo analgesia as healthy controls in terms of magnitude and reproducibility.
It is unclear whether a diagnosis of chronic pain is associated with an increase or decrease in the placebo response. The aim of this study was to use an experimental placebo conditioning paradigm to test whether expectancy for pain relief impacts on acute pain perception in individuals with a chronic pain diagnosis of osteoarthritis (OA) or fibromyalgia (FM), compared to healthy individuals (HIs). An inert cream was applied to the dominant forearm of participants (60 OA, 79 FM, and 98 HI), randomly assigned to either a placebo or control group. ⋯ The results were similar in the repeat session. The results demonstrate that individuals with chronic pain respond to experimental placebo analgesia in a similar and reproducible manner as HIs, despite higher levels of psychological comorbidity. This has implications for using placebo analgesia in the treatment of chronic pain.
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Observational Study
Pain trajectory defines knee osteoarthritis subgroups: a prospective observational study.
Knee osteoarthritis (OA) is a heterogeneous disease, and identification of its subgroups/phenotypes can improve patient treatment and drug development. We aimed to identify homogeneous OA subgroups/phenotypes using pain development over time; to understand the interplay between pain and functional limitation in time course; and to investigate subgroups' responses to available pharmacological and surgical treatments. We used group-based trajectory modelling to identify pain trajectories in the phase-3 VIDEO trial (n = 474, 3-year follow-up) and also in the Osteoarthritis Initiative cohort study (n = 4796, 9-year follow-up). ⋯ Notably, we identified a phenotype with severe pain that did not benefit from available treatments, and another one most likely to benefit from knee replacement. Thus, knee OA subgroups/phenotypes can be identified based on patients' pain experiences in studies with long and regular follow-up. We provided a robust approach, reproducible between different study designs, which informs clinicians about symptom development and delivery of treatment options and opens a new avenue toward personalized medicine in OA.
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Chronic widespread pain conditions are more prevalent in women than men, suggesting a role for gonadal hormones in the observed differences. Previously, we showed that female mice, compared to male, develop widespread, more severe, and longer-duration hyperalgesia in a model of activity-induced muscle pain. We hypothesized testosterone protects males from developing the female pain phenotype. ⋯ We examined potential sex differences in the distribution of SERT across brain sites involved in nociceptive processing using immunohistochemistry. A sex difference in SERT was found in the NRM in the activity-induced pain model; females had greater SERT immunoreactivity than males. This suggests that testosterone protects against development of widespread, long-lasting muscle pain and that alterations in SERT may underlie the sex differences.
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Central poststroke pain (CPSP) is a debilitating and often treatment-refractory condition that affects numerous stroke patients. The location of lesions most likely to cause pain and the identity of the functional brain networks that they impinge upon remain incompletely understood. We aimed to (1) elucidate which lesion locations are most frequently accompanied by pain; (2) explore CPSP-associated functional networks; and (3) examine how neuromodulation interacts with these networks. ⋯ The extent of connectivity to the thalamus, inferior parietal lobule, and precuneus also differed between CPSP and control lesions (PBonferroni < 0.05). Posterior insula and thalamus shared connectivity with both CPSP lesions and pain-alleviating DBS activation volumes (PBonferroni < 0.05). These findings further clarify the topography and functional connectivity of pain-causing brain lesions, and provide new insights into the network-level mechanism of CPSP neuromodulation.
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Chronic posttraumatic headache (PTH) is among the most common and disabling sequelae of traumatic brain injury (TBI). Current PTH treatments are often only partially effective and have problematic side effects. We previously showed in a small randomized trial of patients with chronic nontraumatic headaches that manipulation of dietary fatty acids decreased headache frequency, severity, and pain medication use. ⋯ Statistical analyses assessed the association of oxylipins with headache severity (primary outcome, measured by headache question on NSI) as well as associations between oxylipins and total NSI or satisfaction with life survey scores. Among oxylipins, 4-hydroxy-DHA and 19,20-epoxy-docosapentaenoate (DHA derivatives) were inversely associated with headache severity, and 11-hydroxy-9-epoxy-octadecenoate (a linoleic acid derivative) was positively associated with headache severity. These findings support a potential for DHA-derived oxylipins as prognostic biomarkers for development of chronic PTH.