Anticholinergic-induced chorea in the treatment of focal dystonia.

The occurrence of chorea, induced by trihexyphenidyl (benzhexol hydrochloride) during the treatment of five adult patients who had focal or segmental dystonia, is described. The dose at which chorea appeared ranged from 15 to 60 mg/day (mean 31.7 mg/day). All but one patient had developed common adverse effects of this drug (dry mouth, blurred vision, and confusion) at lower doses (mean 21.8 mg per day). There was an inverse relationship between the age of the patient and the dose of trihexyphenidyl at which chorea developed.