Pain
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Fibromyalgia is a prevalent and burdensome disorder characterized by chronic widespread pain and complex comorbid symptoms. To develop better treatments for pain-centered fibromyalgia symptoms, there is still a need for animal models which mimic the features of fibromyalgia patients. In the present study, we have established a fibromyalgia animal model by utilizing a never-before-published pharmacological effect of reserpine. ⋯ Pregabalin, duloxetine, and pramipexole significantly attenuated the reserpine-induced decrease in muscle pressure threshold, but diclofenac did not. The validity of the use of this reserpinized animal as a fibromyalgia model is demonstrated from three different aspects, i.e., face validity (manifestation of chronic pain and comorbid symptoms), construct validity (dysfunction of biogenic amine-mediated central nervous system pain control is involved), and predictive validity (similar responses to treatments used in fibromyalgia patients). This animal model is expected to contribute to the better understanding of fibromyalgia pathophysiology and the evaluation of drugs, especially those which would activate biogenic amine system.
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Randomized Controlled Trial
Intrathecal glycine for pain and dystonia in complex regional pain syndrome.
Since glycinergic neurotransmission plays an important inhibitory role in the processing of sensory and motor information, intrathecal glycine (ITG) administration may be a potential therapy for both pain and movement disorders in patients with complex regional pain syndrome (CRPS). Aims of the current study, which is the first report on ITG in humans, were to evaluate its safety and efficacy. ITG treatment during 4 weeks was studied in CRPS patients with dystonia in the period before they received intrathecal baclofen treatment. ⋯ Although there was a trend to worsening on the CGI and PGI during ITG treatment, there were no significant differences between ITG and placebo treatment in any of the outcomes. ITG given over 4 weeks was ineffective for pain or dystonia in CRPS. Although no serious adverse events occurred, further studies are required to rule out potential neurotoxicity of ITG.
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Do contrasting neuropathic pain diagnoses share common pathophysiological mechanisms? Selective breeding was used to derive rat lines with a common genetic background but a striking difference in the degree of spontaneous pain behavior expressed in the neuroma model of neuropathic pain (HA rats (high autotomy) and LA rats (low autotomy)). The contrasting pain phenotype in these lines is attributable to allelic differences at a small number of genetic loci. Here we show that HA and LA rats also differ in their nocifensive response to applied stimuli in the Chung (spinal nerve ligation, SNL) model of neuropathic pain. ⋯ F1 crosses of HA and LA rats and inbred Lewis rats showed low levels of autotomy but variable levels of hypersensibility to applied stimuli. Results indicate that alleles which predispose to spontaneous neuropathic pain also predispose to stimulus-evoked pain (allodynia and hyperalgesia). This, in turn, suggests that despite contrasting etiology and behavioral endpoints, pain phenotype in the neuroma and the SNL models shares common pathophysiological mechanisms.
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Placebo has been shown to be a powerful analgesic with corresponding reduction in the activation of the pain matrix in the brain. However it is not clear whether the placebo response is reproducible within individuals and what role personality traits might play in predicting it. We induced placebo analgesia by conditioning subjects to expect pain reduction following a sham-treatment in the guise of a local anaesthetic cream applied to one arm. ⋯ A regression model was used to statistically define a placebo responder in terms of personality scores. High dispositional optimism and low state anxiety were found to be significant predictors of placebo response. We suggest that repeated placebo responders are high in dispositional optimism and having a placebo response in the first session causes a drop in state anxiety at the beginning of the repeat session.
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Investigated was the relationship between pain catastrophizing and pain intensity in adolescents suffering from chronic pain (n = 38) and the extent to which they expressed communicative pain and pain-related protective behaviours. Adolescents were observed on video performing a 2-Min Walk Test (2MWT). Behaviours were coded on videotape. ⋯ Pain-related protective behaviours did not vary with the adolescents' level of pain catastrophizing, but varied with pain intensity. The findings corroborate the functional distinctiveness of different types of pain behaviours. The results are discussed in terms of the processes linking (1) catastrophizing to communicative pain behaviours and (2) pain to pain-related protective behaviours.