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The emerging use of botulinum toxins for the treatment of neuropathic pain.

There has been increasing interest in exploring the potential therapeutic benefit of the botulinum toxins in the management of neuropathic pain. Examples of neuropathic pain include painful diabetic polyneuropathy, postherpetic neuralgia (PHN), complex regional pain syndrome, trigeminal neuralgia and neuropathic low back pain. Other chronic pain syndromes may exhibit neuropathic features including migraine and fibromylagia but are not considered by most to be typical neuropathic pain states [1–3]. Xiao et al. in this issue of Pain Medicine report the results of their randomized controlled study evaluating the effect of subcutaneous injections of botulinum toxin type A (BOTOX) compared with lidocaine and placebo injections for the treatment of PHN [4]. As has been outlined elsewhere in this issue by Xiao et al., BOTOX is known to have analgesic properties with an increasing awareness of proposed mechanisms that underlie these analgesic benefits.

Neuropathic pain is often associated with other chronic pain syndromes, which may be effectively treated with botulinum toxins, in particular, myofascial pain. Allen et al. have demonstrated that 56% of 134 patients with CRPS type 1 demonstrated evidence of myofascial pain in association with their neuropathic pain [5]. This not only confirmed that different types of pain may co-exist within the same patient and that one type of pain, e.g., neuropathic pain may lead to and become associated with another type of pain, but it led to the consideration of how these observations might lead to more effective treatment.

Muscle nociceptors are known to become sensitized by substances including bradykinin and prostaglandins as well as others similar to that seen in neuropathic pain. One investigator has emphasized the role of autonomic nervous system dysfunction …