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Drug-induced dystonic reactions are seen:

• as an acute reaction, often of the torsion type, and occur following administration of dopamine receptor blocking antipsychotics, e.g. haloperidol, and antiemetics, e.g. metoclopramide. An antimuscarinic drug, e.g. biperiden or benzatropine, given i.m. or i.v. and repeated as necessary, provides relief

• in some patients who are receiving levodopa for Parkinson's disease

• in younger patients on long-term antipsychotic treatment, who develop tardive dyskinesia (see p. 387).

Hepatolenticular degeneration (Wilson's disease) is caused by a genetic failure to eliminate copper absorbed from food so that it accumulates in the liver, brain, cornea and kidneys. Chelating copper in the gut with penicillamine (p. 293) or trientine can establish a negative copper balance (with some clinical improvement if treatment is started early). The patients may also develop cirrhosis, and the best treatment for both may be orthotopic liver transplantation.

Chorea of any cause may be alleviated by dopamine receptor blocking antipsychotics, and also by tetrabenazine, which inhibits neuronal storage of dopamine and serotonin.

Involuntary muscle spasm: blepharospasm, hemifacial spasm, spasmodic torticollis, and indeed the spasm of chronic anal fissure, are treated with botulinum toxin. This irreversibly blocks release of acetylcholine from cholinergic nerve endings and is injected locally. Its effect lasts about 3 months. Botulinum toxin is at least partially effective in up to 90% of patients with these conditions. Mild dysphagia occurs in ~30% of patients receiving injections into their neck for torticollis due to spread of the toxin in to the pharyngeal muscles.

Spasticity results from lesions at various sites within the central nervous system and spinal cord. Drugs used include the GABA agonist baclofen, diazepam and tizanidine (an a2-adrenoceptor agonist).

Myotonia in which voluntary muscle fails to relax after contraction may be symptomatically benefitted by drugs that increase muscle refractory period, e.g. procainamide, phenytoin, quinidine.

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