Pain
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The ultraviolet B (UVB) sunburn model was characterized with a comprehensive battery of quantitative sensory testing (QST). Primary hyperalgesia in UVB-irradiated skin and secondary hyperalgesia in adjacent nonirradiated skin were studied in 22 healthy subjects 24h after irradiation with UVB at 3-fold minimal erythema dose of a skin area 5 cm in diameter at the thigh and compared to mirror-image contralateral control areas. The time course of hyperalgesia over 96 h was studied in a subgroup of 12 subjects. ⋯ Although of smaller magnitude, secondary hyperalgesia and dynamic mechanical allodynia adjacent to the UVB-irradiated area were statistically highly significant. Primary and secondary hyperalgesia developed in parallel within hours, peaked after 24-32 h, and lasted for more than 96 h. These data reveal that the UVB sunburn model activates a broad spectrum of peripheral and central sensitization mechanisms and hence is a useful human surrogate model to be used as a screening tool for target engagement in phases 1 and 2a of drug development.
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People with chronic pain and comorbid posttraumatic stress disorder (PTSD) report more severe pain and poorer quality of life than those with chronic pain alone. This study evaluated the extent to which associations between PTSD and chronic pain interference and severity are mediated by pain-related coping strategies and depressive symptoms. Veterans with chronic pain were divided into 2 groups, those with (n=65) and those without (n=136) concurrent PTSD. ⋯ Illness-focused pain coping also evidenced specific mediating effects, independent of depression. In summary, specific pain coping strategies and depressive symptoms partially mediated the relationship between PTSD and both pain interference and severity. Future research should examine whether changes in types of coping strategies after targeted treatments predict improvements in pain-related function for chronic pain patients with concurrent PTSD.
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The combined oral contraceptive pill (COCP) has been implicated in the development of a number of chronic pain conditions. Modern COCP formulations produce a low endogenous estradiol, low progesterone environment similar to the early follicular phase of the natural menstrual cycle, with a variable effect on serum androgen levels. We used behavioural measures and functional magnetic resonance imaging to investigate the response to experimental thermal stimuli in healthy women, in both a natural and COCP-induced low endogenous estradiol state, to investigate whether alterations in central pain processing may underlie these observations in COCP users. ⋯ Of particular interest, in COCP users, activity in the rostral ventromedial medulla increased with increasing testosterone and in those women with low testosterone, was significantly reduced compared to controls. These findings suggest that, in a low endogenous estradiol state, testosterone may be a key factor in modulating pain sensitivity via descending pathways. Specifically, failure to engage descending inhibition at the level of the rostral ventromedial medulla may be responsible for the reduction in temperature required by COCP users with low circulating testosterone.
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Randomized Controlled Trial Comparative Study
The role of fear of movement in subacute whiplash-associated disorders grades I and II.
Fear and avoidance of activity may play a role in fostering disability in whiplash-associated disorders (WAD). This study examined the role of fear after WAD and assessed the effectiveness of 3 treatments targeting fear. People still symptomatic from WAD grade I-II injuries approximately 3months previously (n=191) completed questionnaires (eg, Neck Disability Index [NDI]) and were randomized to 1 of the treatments: (1) informational booklet (IB) describing WAD and the importance of resuming activities, (2) IB+didactic discussions (DD) with clinicians reinforcing the booklet, and (3) IB+imaginal and direct exposure desensitization (ET) to feared activities. ⋯ Reduction in fear was the most important predictor of improvement in NDI (β=0.30, P<.001), followed by reductions in pain (β=0.20, P=.003) and depression (β=0.18, P=.004). The mediational analysis confirmed that fear reduction significantly mediated the effect of treatment group on outcome. Results highlight the importance of fear in individuals with subacute WAD and suggest the importance of addressing fear via exposure therapy and/or educational interventions to improve function.
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The sexes differ with respect to perception of experimental pain. Anxiety influences pain perception more in men than in women; however, there lacks research exploring which anxiety constructs influence pain perception differentially between men and women. Furthermore, research examining whether depression is associated with pain perception differently between the sexes remains scant. ⋯ Depression was not systematically associated with pain perception in either sex. Systematic relationships were not identified that allow conclusions regarding how fear of pain, pain-related anxiety, and anxiety sensitivity may contribute to pain perception differentially in men and women; however, anxiety sensitivity was associated with increased pain tolerance, a novel finding needing further examination. The results provide directions for future research and clinical endeavors and support that fear and anxiety are important features associated with hyperalgesia in both men and women.