Pain
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In a longitudinal observational study of 94 patients (39 M:55 F, mean age 69) at elevated risk for developing post herpetic neuralgia (PHN), the natural history of pain during the first 6 months after herpes zoster (HZ) rash onset was determined. Pain severity and impact were rated using pain-VAS, SF-MPQ, and MPI. Applying a definition of PHN of average daily pain >0/100 on the pain VAS during the last 48 h, 30 subjects had PHN at 6 months. ⋯ At study inclusion, the SF-MPQ and MPI scores in our PHN group were similar to historical controls with chronic severe PHN enrolled in clinical trials, but by 6 months the scores in our PHN subjects were significantly lower than historic controls. Only two subjects met the more stringent criteria for 'clinically meaningful' PHN at 6 months (> or = 30/100 on the pain VAS). Defining PHN as average daily pain >0/100 at 6 months after rash onset appears to substantially overestimate the number of HZ patients negatively impacted by ongoing pain and disability.
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Previous neuroimaging studies have shown brain activity during not only the application of noxious stimuli, but also prior to stimulation. The functional significance of the anticipatory response, however, has yet to be explored. Two theoretical responses involve either a decrease or an increase in sensitivity of the nociceptive system. ⋯ Results of this regression analysis revealed that insula activity during receipt was predicted by activity in both the entorhinal cortex and VTA during anticipation. We suggest that activation in both regions before and during pain may underlie anticipation and subsequent pain modulatory responses, possibly involving the appraisal and control of attention necessary for pain modulation. Together, the results suggest a possible role of brainstem areas in anticipatory mechanisms involved in the maintenance of chronic pain.
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Randomized Controlled Trial
Classical conditioning and expectancy in placebo hypoalgesia: a randomized controlled study in patients with atopic dermatitis and persons with healthy skin.
The effectiveness of placebos is unchallenged. However, it is still not clear on which mechanisms the placebo effect is based. Besides expectancy theories, classical conditioning is discussed as a major explanatory model. ⋯ However, conditioning processes seem to be necessary for a longer lasting effect. The extent of this effect seemed to be greater in atopics than in healthy controls. Expectancy, achieved through verbal instruction, might also be seen as a conditioned stimulus that reactivates earlier stimulus associations.
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Little is known about the pathway from musculoskeletal pain to mobility difficulty among older persons. We examined potential physical and psychological mediators of the pain-disability relationship in the Women's Health and Aging Study (WHAS), a cohort of women aged 65 who had at least mild disability at baseline. Pain was classified according to location and severity (widespread pain; lower extremity pain; other pain; none or mild pain in only one site). ⋯ Pain was not associated with increased risk for becoming unable to walk or climb stairs. The findings suggest that pain is a unique domain as a cause of disablement, independent of the usual pathway to disability via physical impairments. Research is needed to better understand the development of pain-related disability in order to determine optimum approaches to prevent and treat mobility disability in older persons with persistent pain.
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Noxious C-fibre stimulation produces increased sensitivity within the injured area (primary hyperalgesia), and a surrounding zone of secondary hyperalgesia. As significant changes in nociceptive processing occur during development, we compared C-fibre induced primary and secondary hyperalgesia in rat pups aged 3, 10 and 21 postnatal (P) days. Hyperalgesia was measured by electromyography flexion reflex recordings following mustard oil or capsaicin at the site of (primary hyperalgesia), or distant to (secondary hyperalgesia) hindpaw mechanical stimuli. ⋯ These results provide evidence that primary and secondary hyperalgesia are differentially modulated during development. Furthermore, since ERK activation is required for secondary hyperalgesia, phosphoERK expression can be used to map the spatial distribution of neuronal activation in the spinal cord. Understanding changing responses to injury in the developing nervous system is important for clinical paediatric practice, and will enhance our ability to target the most effective site with a developmentally appropriate analgesic regime.