The journal of pain : official journal of the American Pain Society
-
Allergic contact dermatitis (ACD) is a common condition that can significantly affect the quality of life. Contact with allergens results in delayed hypersensitivity reactions involving T lymphocytes, with associated skin inflammation and spontaneous itch and nociceptive sensations. However, psychophysical studies of these sensations are lacking. In the present study, we sensitized 8 healthy volunteers to squaric acid dibutyl ester (SADBE). Two weeks later, 1 volar forearm was challenged with SADBE, and the other with acetone vehicle control. Subsequently, participants rated the maximal perceived intensity of spontaneous itch, pricking/stinging, and burning every 6 to 12 hours for 1 week, using the generalized Labeled Magnitude Scale. In the laboratory, they judged stimulus-evoked sensations within and outside the chemically treated area. The SADBE- but not the acetone-treated skin resulted in 1) localized inflammation, with spontaneous itch and nociceptive sensations peaking at 24 to 48 hours after challenge, 2) alloknesis, hyperknesis, and hyperalgesia to mechanical stimuli that were reduced or eliminated by anesthetic cooling of the SADBE-treated area and restored on rewarming, suggesting that sensations and dysesthesias are dependent on ongoing peripheral neural activity, and 3) enhanced itch to intradermal injection of histamine, BAM8-22, or β-alanine. This experimental model of T-cell-mediated inflammation may prove useful in evaluating potential treatments of itch from ACD. ⋯ In a model of allergic contact dermatitis, experimentally applied in humans, psychophysical measurements were obtained of persistent, spontaneous itch and enhanced stimulus-evoked itch and pain sensations. These sensory measurements will be useful in the identification of the neural mechanisms underlying inflammatory itch and pain.
-
Habituation and sensitization are important features of individual sensitivity to repetitive noxious stimulation and have been investigated in numerous studies. However, it is unclear whether these phenomena vary depending on the site of stimulation. Here we compared short-term and long-term effects of painful heat stimulation on the forehead and limb using an established longitudinal heat pain paradigm performed over 8 consecutive days in 36 healthy volunteers. Participants were randomized into 2 groups; participants received repetitive heat pain stimulation either on the left volar forearm or on the left side of the forehead. Our data show a comparable degree of habituation over the course of 8 days in both groups. However, participants in the trigeminal stimulation group exhibited stronger within-session sensitization (indexed by a higher within-session increase in pain intensity ratings) than those who received the forearm stimulation. Furthermore, over the course of the experiment we found a correlation between habituation and anxiety, showing less habituation in participants with higher trait anxiety scores. Our findings are in line with somatotopic differences in response to painful stimulation and a higher proneness of trigeminal pain to sensitization processes, which might be explained by the biological relevance of the head and facial area for vital functions. The contribution of this sensitivity to the development and maintenance of clinical facial pain and headache disorders warrants further investigation. ⋯ This study uses psychophysical methods to evaluate the differences in long-term habituation and short-term sensitization to heat pain between the trigeminal and spinal systems. We found stronger sensitization for trigeminal compared with nociceptive stimuli on the forearm. The contribution of this sensitivity to clinical pain states warrants further investigation.
-
Omega-3 and omega-6 fatty acids are biosynthetic precursors of endocannabinoids with antinociceptive, anxiolytic, and neurogenic properties. We recently reported that targeted dietary manipulation-increasing omega-3 fatty acids while reducing omega-6 linoleic acid (the H3-L6 intervention)-reduced headache pain and psychological distress among chronic headache patients. It is not yet known whether these clinical improvements were due to changes in endocannabinoids and related mediators derived from omega-3 and omega-6 fatty acids. We therefore used data from this trial (N = 55) to investigate 1) whether the H3-L6 intervention altered omega-3- and omega-6-derived endocannabinoids in plasma and 2) whether diet-induced changes in these bioactive lipids were associated with clinical improvements. The H3-L6 intervention significantly increased the omega-3 docosahexaenoic acid derivatives 2-docosahexaenoylglycerol (+65%, P < .001) and docosahexaenoylethanolamine (+99%, P < .001) and reduced the omega-6 arachidonic acid derivative 2-arachidonoylglycerol (-25%, P = .001). Diet-induced changes in these endocannabinoid derivatives of omega-3 docosahexaenoic acid, but not omega-6 arachidonic acid, correlated with reductions in physical pain and psychological distress. These findings demonstrate that targeted dietary manipulation can alter endocannabinoids derived from omega-3 and omega-6 fatty acids in humans and suggest that 2-docosahexaenoylglycerol and docosahexaenoylethanolamine could have physical and/or psychological pain modulating properties.
-
Population-based studies suggest that pain in the lower body is common and that pain at multiple sites is more prevalent than single-site pain. Obesity is a risk factor for multisite musculoskeletal pain, but there are limited data on the role of body composition. Therefore, we sought to determine whether body composition is associated with multisite musculoskeletal pain involving the low back, knee, and foot. A total of 133 participants were recruited for a study examining the relationship between obesity and musculoskeletal disease. Participants completed validated questionnaires that examined levels of pain at the low back, knee, and foot. Body composition was assessed using dual-energy x-ray absorptiometry. Multisite pain was common, with 26.3% of participants reporting pain at 2 sites and 31.6% at 3 sites, and only 20% were pain free. The low back was the most common site of pain (63%). Greater fat mass and fat mass index, but not fat-free mass, were associated with pain at a greater number of sites, independent of age, gender, and fat-free mass (P < .01). Longitudinal studies exploring the mechanism of action by which increased fat mass is associated with pain may provide important insights into therapeutic strategies for the prevention of multisite pain. ⋯ Greater fat mass and fat mass index were associated with a greater number of lower body pain sites, with no association observed for fat-free mass. Understanding the mechanism by which increased fat mass is associated with pain may provide important insights into therapeutic strategies for the prevention of pain.