Pain
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Reports of RCTs of analgesics frequently describe results of studies in the form of mean derived indices, rather than using discontinuous events--such as number or proportion of patients with 50% pain relief. Because mean data inadequately describe information with a non-normal distribution, combining mean data in systematic reviews may compromise the results. Showing that dichotomous data can reliably be derived from mean data, at least in acute pain models, indicates that more meaningful overviews or meta-analysis may be possible. ⋯ Mean %maxTOTPAR correlated with the proportion of patients with > 50%maxTOTPAR (r2 = 0.90). The relationship calculated from all the 45 treatments predicted to within three patients the number of patients with more than 50% pain relief in 42 of 45 treatments, and 98.8% of 10,000 simulated treatments. For seven effective treatments, actual numbers-needed-to-treat (NNT) to achieve > 50%maxTOTPAR compared with placebo were very similar to those derived from calculated data.
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Clinical Trial
Influence of previous pain experience on the episode incidence of low back pain: results from the South Manchester Back Pain Study.
A pathological cause cannot be identified for most new episodes of low back pain (LBP) presenting to the general practitioner. One important potential influence on susceptibility is previous pain experience. To accurately investigate the contribution of this phenomenon to the onset of new episodes of LBP a prospective population study is required. ⋯ In those currently free of LBP a previous history of the symptom substantially increases the risk of a further episode, with pain in other sites an equally strong independent predictor of subsequent LBP.
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Pain experienced in a limb prior to amputation may influence the course of phantom limb pain many months later. Katz and Melzack (1990) found that 42% of their sample reported a 'somatosensory pain memory' which resembled the quality and location of a painful, or non-painful pre-amputation sensation. For many amputees, pain memories are vivid experiences which incorporate both emotional and sensory aspects of the pre-amputation pain (Katz 1992). ⋯ The present case study used a diary design to examine whether 'triggers' could be identified for somatosensory pain memories. Over a 9-month period, the patient reported daily experience of ongoing phantom limb pain, generally confined to the distal part of the limb, and 5 episodes of injury-related phantom limb pain, primarily experienced in the calf of the missing limb. A 'trigger' was identified for each of the episodes of injury-related phantom limb pain, and a significant finding in this study was that two episodes of injury-related phantom limb pain were associated with cognitive and/or emotional, rather than sensory 'triggers'.
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Recent studies have reported a high prevalence of symptoms of post-traumatic stress disorder (PTSD) among individuals with chronic pain. Studies suggest that persons with pain and PTSD also display higher levels of affective disturbance. In the present study we examined self-reports of pain, affective disturbance, and disability among pain patients with and without symptoms of PTSD. ⋯ These findings suggest that PTSD symptoms in chronic pain patients are associated with increased pain and affective distress. Accident related pain, even without the presence of PTSD symptoms, appears to be associated with greater disability. The results indicate that the identification and treatment of PTSD symptoms in refractory pain patients may be a critical albeit subtle factor in the effective management of suffering and disability in this population.
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Behavioral and electrophysiological methods were used to investigate the hyperalgesia and allodynia, and functional changes in lumbar spinal dorsal horn neurons, in a model of neuropathic pain (Selzer et al. 1990) involving ligation of one-third to one-half of one sciatic nerve in rats. One and 5 weeks following ligation, there was a significant reduction in hind limb withdrawal latency to noxious radiant heat on the operated side and, to a lesser degree, on the unoperated side. By 16 weeks, heat withdrawal latencies were reduced about equally (approximately 40%) on both sides. ⋯ Mechanical receptive field areas were not significantly different between ipsi- and contralateral sides in the sham and 5-week post-ligation groups, or between sham and 5-week post-ligation groups. However, receptive field areas were significantly larger in the 16-week post-ligation group (both ipsi- and contralateral to ligation) compared to sham and 5-week post-ligation groups. The results suggest that allodynia may be associated with a chronic enhancement of neuronal mechanosensitivity, but that the thermal hyperalgesia is not associated with enhanced neuronal responsiveness or force of withdrawal.