The Clinical journal of pain
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Temporomandibular disorder (TMD) is a collective term used to characterize a heterogeneous group of conditions involving the temporomandibular joint (TMJ) and its contiguous tissues. Although the pathologies behind TMDs have not been completely explained, the symptoms associated with these disorders are similar and are most commonly manifest as pain in the orofacial region. ⋯ This article describes common TMDs and their treatment with botulinum toxin. Dosing guidelines and illustrations of affected muscles and target injection sites are provided.
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Understanding the pathophysiology of a pain syndrome is helpful in selecting appropriate treatment strategies. Nociceptive pain is related to damage to tissues due to thermal, chemical, mechanical, or other types of irritants. Neuropathic pain results from injury to the peripheral or central nervous system. ⋯ A clear benefit of botulinum toxin therapy for treatment of neuropathic pain disorders is that it often relieves pain symptoms. Although the precise mechanism of pain relief is not completely understood, the injection of botulinum toxin may reduce various substances that sensitize nociceptors. As a result, botulinum toxin types A and B are now being actively studied in nociceptive and neuropathic pain disorders to better define their roles as analgesics.
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An overview is presented of neuropathic pain syndromes, their characteristic symptoms and signs, and recent approaches to identifying their pathophysiologic mechanisms. ⋯ Precise estimates of the prevalence of neuropathic pain are not available, but chronic neuropathic pain may be much more common than has generally been appreciated and its prevalence can be expected to increase in the future. There is considerable agreement that both peripheral and central processes contribute to many chronic neuropathic pain syndromes, and that these different mechanisms may explain the qualitatively different symptoms and signs that patients experience. The limitations of existing treatments for neuropathic pain and the inability to provide relief for many patients has stimulated ongoing studies that examine different approaches to preventing neuropathic pain.
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The immune system is unable to determine whether material it encounters is deleterious, benign, or even beneficial to the organism. This presents a significant challenge when protein-based biological therapies, such as botulinum toxin, are administered to patients. Many factors combine to influence the likelihood and the magnitude of an immune response if a response is elicited. ⋯ The majority of anti-toxin antibodies do not affect its function. Finally, although crossreactivity has been reported among the seven botulinum toxin serotypes, non-neutralizing antibodies are present that recognize regions of similarity among the serotypes. No cross-neutralizing antibodies have been described in patients administered any of the toxin serotypes.
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Chronic pain is a prevalent and costly problem. This review addresses the question of the clinical effectiveness and cost-effectiveness of the most common treatments for patients with chronic pain. ⋯ There are limitations to the success of all the available treatments. The author urges caution in interpreting the results, particularly in comparisons between treatments and across studies, because there are broad differences in the pain syndromes and inclusion criteria used, the drug dosages, comparability of treatments, the definition of "chronic" used, the outcome criteria selected to determine success, and societal differences. None of the currently available treatments eliminates pain for the majority of patients. Pain rehabilitation programs provide comparable reduction in pain to alternative pain treatment modalities, but with significantly better outcomes for medication use, health care utilization, functional activities, return to work, closure of disability claims, and with substantially fewer iatrogenic consequences and adverse events. Surgery, spinal cord stimulators, and IDDSs appear to have substantial benefits on some outcome criteria for carefully selected patients. These modalities are, however, expensive. Pain rehabilitation programs are significantly more cost effective than implantation of spinal cord stimulators, IDDSs, conservative care, and surgery, even for selected patients. Research is needed to identify which patients are most likely to benefit from the available treatments and to study combinations of the available treatments since none of them appear capable of eliminating pain or significantly improving functional outcomes for all treated.