Botulinum toxin is a product of the anaerobe Clostridium Botulinum and is indicated for the treatment of cervical dystonia, blepharospasm, hemifacial spasm, axillary hyperhidrosis, and glabellar wrinkles. A number of immu-nologically distinct serotypes exist of which type A and type B are the predominant forms in clinical practice. At least some of its effect is due to its ability to inhibit release of acetylcholine from cholinergic nerve terminals. In addition, it has been suggested that it may also inhibit glutamate release, as well as that of calcitonin gene-related peptide and substance P. Animal experimentation has shown that, as well as having muscle relaxant effects, botulinum toxin type A can have marked anti-allodynic effects after a single injection which persists for up to 3 weeks in a chronic nerve constriction model of neuropathic pain. In addition, it can reduce both the acute and chronic response to formalin injection in a rat paw.
As well as those conditions for which it has an indication, there are a number of others for which evidence, of varying strengths, exists for a pain-reducing effect:
• Cluster headache
• Chronic daily headache
• Piriformis muscle spasm
• Temperomandibular joint dysfunction
• Chronic low back pain
• Myofascial pain
• Complex regional pain syndrome
• Postherpetic neuralgia
• Spinal cord injury pain
It should be emphasized that some of the reports of successful use of botulinum toxin in these conditions report its use in a small number of patients and therefore its use in these conditions is speculative rather than heavily evidence based.
Perhaps one of the most unusual pain uses of botulinum toxin is that of intra-articular injection in patients with refractory joint pain with refractory being defined as unresponsive to conventional oral and intra-articular therapy. In one report of just eleven patients, five with osteoarthritis, five with rheumatoid arthritis, and one with psoriatic arthritis, maximal relief was seen with shoulder injection, while lower extremity joint injection was associated with a lesser, but clinically useful, reduction in pain and increase in range of movements. The duration of pain relief ranged from 3 to 12 months.
It would seem that given the well-proven effects of botulinum toxin on specific types of muscle spasm that it should be considered in conditions where any muscle spasm is present. The benefits of use include one-off injections that may give prolonged relief and the possibility of reducing or stopping orally administered muscle relaxant medication.
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