Botulinum toxin in clinical practice.

Over recent years botulinum toxin type A has emerged as a safe and effective treatment for a number of previously refractory conditions associated with excessive muscle activity. The list of indications is expanding, but at present it is generally considered to be the treatment of choice for focal dystonias such as blepharospasm, torticollis, laryngeal dystonia, and oromandibular dystonia, as well as hemifacial spasm, strabismus, and some forms of limb spasticity. Carefully targeted intramuscular injections of a small amount of the toxin block the release of acetylcholine at the neuromuscular junction, producing a chemical denervation, with the aim of reducing excessive muscle activity without producing significant functional weakness. In some situations electrophysiological assessment and localisation of the muscles for injection is necessary. Treatment is symptomatic, with effects lasting 3 to 4 months and most patients requiring up to 4 injections per year to maintain the beneficial effect. Appropriate use of the toxin requires both an understanding of the physiological action of the potential muscles involved in each situation, together with a knowledge of the likely dose necessary to reduce muscle activity to the required level. Botulinum toxin represents a major advance in the management of these conditions, many of which responded poorly to previously available forms of therapy.