Effects of anticholinergic agents on patients with tardive dyskinesia and concomitant drug-induced parkinsonism.

Twenty-five percent of 80 consecutive patients who met research criteria for persistent tardive dyskinesia (TD) were found to have an energy peak in the parkinsonian tremor band (3-6 Hz) of the frequency spectrum of their machine-measured resting hand movements in addition to the abnormalities consistent with TD (increased energy in the 0.5-3 Hz frequency spectrum). Twelve of these patients were studied again in double-blind fashion 2 hours after receiving a placebo and again 2 hours after a single 4 mg dose of trihexyphenidyl hydrochloride (HCl). Compared with the placebo condition, the trihexyphenidyl HCl markedly diminished the measured energy in the 4 Hz band and had no effect or slightly decreased the energy at all other points on the frequency spectrum. Simultaneous Abnormal Involuntary Movement Scale ratings revealed no change in the dyskinetic movements between the conditions; there was a significant subjective improvement reported by the patients following the trihexyphenidyl HCl administration. These observations indicate that electromechanical devices identify a subpopulation of TD patients who may acutely benefit from anticholinergic treatment.