Pain
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The aim of this study was to determine if the application of mustard oil (MO), a small-fiber excitant and inflammatory irritant, or other algesic chemicals (capsaicin, CAP, and bradykinin, BK) to the rat maxillary molar tooth pulp induces electromyographic (EMG) activity of the masseter and digastric muscles, and also to determine if endogenous opioid mechanisms may be involved in any documented EMG changes. Application of MO to the tooth pulp induced a significant increase in EMG activity of the ipsilateral masseter up to 30 min. The application of mineral oil to the pulp or MO application to the pulp-extirpated tooth did not induce any significant EMG increases. ⋯ These findings suggest that pulp afferent inputs to the central nervous system evoked by BK. CAP and especially MO may induce enhanced jaw muscle activity. In addition, the naloxone data suggest that an opioid suppresive mechanism may be induced by the pulpal afferent inputs evoked by MO, and may serve to limit the jaw muscle activity elicited by these inputs.
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Complex regional pain syndrome (CRPS) remains a poorly understood chronic pain disorder. Little data has been published assessing the epidemiology of CRPS (and reflex sympathetic dystrophy, RSD). This study assessed epidemiological variables in 134 CRPS patients evaluated at a tertiary chronic pain clinic in the US, including demographic, health care utilization and legal/workman's compensation measures. ⋯ The duration of CRPS symptoms and the involvement of the upper extremity was significantly associated with the presence of myofascial dysfunction. Thus, this study found that most CRPS patients are referred to a pain specialty clinic after several years of symptoms and many failed therapies. The data also suggest the lack of utility of a diagnostic bone scan and highlight the prominence of myofascial dysfunction in a majority of CRPS patients.
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Corticosteroids are probably an effective treatment for some types of neuropathic pain and complex regional pain syndromes. This study examined the effects of systemic methylprednisolone (MP) on acute nociception and on pain behavior and hyperalgesia in normal and neuropathic rats. There was no dose-response to intraperitoneal MP (up to 12 mg/kg) for nociceptive thresholds to heat (Peltier) or mechanical (analgesy-meter and von Frey fibers) stimuli in normal rats. ⋯ These results demonstrate that corticosteroids did not affect nociceptive thresholds in normal or neuropathic hyperalgesic rats. Chronic steroid treatment did prevent the development of autotomy and neuropathic edema, and completely blocked neurogenic extravasation, findings consistent with the hypothesis that primary afferent substance P release mediates autotomy pain behavior and neuropathic edema. This may be a relevant model for examining the effects of corticosteroids on neuropathic pain and complex regional pain syndromes.
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We investigated behavioral symptoms of neuropathic pain, and associated changes in dorsal horn neurons, in a rat model involving loose ligation of lumbar dorsal roots. The L4-L6 dorsal roots were exposed unilaterally and loosely constricted central to the respective ganglia with one (1-ligation) or two (2-ligation) silk 7-O ligatures. In control groups the dorsal roots were exposed but not ligated (sham-operated), or sutures were placed lengthwise between the dorsal roots (suture control). ⋯ Enlarged cutaneous receptive fields of dorsal horn neurons may contribute to mechanical allodynia associated with dorsal root constriction. However, the slow (>5 week) development of receptive field enlargement does not match the rapid development of allodynia. The lack of effect of dorsal root constriction on thermal sensitivity of dorsal horn units ipsilaterally corresponds to the lack of marked thermal hyperalgesia observed behaviorally.
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Pulse radiofrequency has been recently described as a technique to apply a relatively high voltage near a nerve but without the usual effects of a rise in temperature or subsequent nerve injury. In this set of case reports, the effect of pulsed radiofrequency (PRF) is described in patients with neuropathic pain syndromes which have been poorly controlled with other oral and invasive treatments. Whilst anecdotal, the results have been remarkable and should encourage further research into this technique. Observations from the basic science tend to support the concept that PRF may induce some sort of long-term depression in the spinal cord.