The journal of pain : official journal of the American Pain Society
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Clinical Trial Controlled Clinical Trial
Effects of the N-methyl-D-aspartate receptor antagonist dextromethorphan on temporal summation of pain are similar in fibromyalgia patients and normal control subjects.
Temporal summation of second pain at least partly reflects temporal summation of dorsal horn neuronal responses, and both have been termed windup (WU), a form of nociception-dependent central sensitization. Animal and human experiments have shown that both forms of WU depend on N-methyl-D-aspartate (NMDA) and substance P receptor systems. WU of second pain (WU(SP)) in patients with fibromyalgia (FM) is enhanced compared with normal control (NC) subjects and is followed by exaggerated WU(SP) aftersensations and prolonged WU(SP) maintenance at low stimulus frequencies. Because the enhanced WU(SP) of FM patients could be related to abnormal endogenous modulation of NDMA receptors, we tested the effects of the NMDA receptor antagonist dextromethorphan (DEX) on WU(SP) in FM and NC subjects in a double-blind, placebo-controlled, crossover study. WU(SP) was elicited by trains of 0.7-second duration thermal pulses applied to the glabrous surface of the hands or by 1-second mechanical stimuli to the adductor pollicis muscle of the hands at a frequency of 0.33 Hz. In comparison to baseline and placebo conditions, single oral doses of DEX 60 and 90 mg reduced thermal and mechanical WU(SP) in NC and FM subjects, with DEX 90 mg being most effective. These effects did not differ for male and female NC subjects. FM subjects required less thermal and mechanical stimulus intensity than NC to achieve maximal WU(SP), but the extent of WU(SP) reduction by DEX did not statistically differ between NC and FM subjects for all study conditions. Thus, central pain processing of FM subjects is not different from NC in at least one important aspect, namely their NMDA receptor system responsiveness to pharmacologic inhibition by DEX. ⋯ Results of this study demonstrate that FM patients show abnormal WU(SP) during thermal and mechanical stimulation compared with NC. Because oral doses of the NMDA receptor antagonist DEX attenuated thermal and mechanical WU(SP) similarly in FM patients and NC, other mechanisms than WU(SP) need to be considered for the widespread pain of FM patients. These mechanisms might include tonic nociceptive input from peripheral tissues and/or enhanced descending facilitation.
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The present study sought to investigate to what extent patients with chronic low back pain and pain-free control subjects selectively attend to pain-related stimuli as measured with 2 dot-probe tasks with word stimuli and pictorial stimuli. Selective attentional processing was measured by means of 3 indices: the bias index, a congruency effect, and an incongruency effect. Pain-related fear as a trait measure (Tampa Scale for Kinesiophobia [TSK]) was expected to be positively associated with all indices of selective attentional processing of pain stimuli. Results were analyzed with repeated-measures analysis of variance. An incongruency effect was found for patients and to a significantly less degree for pain-free control subjects on the dot-probe task with pictorial stimuli, indicating that pain patients have difficulty disengaging from threat pictures. Pain-related fear as a trait measure (TSK) was not associated with selective attentional processing of word and pictorial stimuli in either pain patients or control subjects. Results from the present study are discussed, and directions for future research are provided. ⋯ Demonstrating difficulty to disengage from threat might be clinically relevant because patients might pay less attention to fear-disconfirming information and remain engaged in avoidance, which might eventually lead to prolonged anxiety states.
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Case Reports
Botulinum toxin a injection of the obturator internus muscle for chronic perineal pain.
Chronic perineal pain is often a difficult condition to manage. Current treatments include pudendal nerve injections and pudendal nerve release surgery. The obturator internus muscle has a close relationship to the pudendal nerve and might be a potential target for therapeutic intervention. ⋯ A case is presented of refractory perineal pain that was successfully treated by injecting the obturator internus muscle with botulinum toxin A.
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Operant behavioral models of chronic pain posit that the pain behaviors and disability of patients with chronic pain can be influenced by social contingencies, such as significant others' responses to pain and well behaviors. The aim of the present study was to develop and evaluate a comprehensive measure of spouse responses to patient pain and well behaviors, the Spouse Response Inventory (SRI). One hundred four patients with chronic pain and their spouses completed a battery of questionnaires, including the SRI. The final analysis yielded a 39-item inventory divided into 4 scales that assess spouse solicitous and negative responses to patient pain behaviors and spouse encouraging and negative responses to patient well behaviors. Analyses yielded results that were consistent with previous research demonstrating an association between spouse solicitous and negative responses to patient pain behaviors and measures of patient functioning, providing preliminary support for the validity of the SRI scales. The results are discussed in terms of implications for further research and the clinical applicability of the SRI. ⋯ This article presents the psychometric properties of a new measure of spouse responses to patient chronic pain and well behavior. This measure could potentially be helpful to clinicians seeking to assess the extent to which spouse responses may contribute to patient pain and disability and also to researchers who wish to test hypotheses derived from operant theory as applied to chronic pain.