Iatrogenic parkinsonism in Huntington's chorea

This case report describes a 63 year old woman with a nineteen year history of Huntington's Chorea who had been successfully treated with tetrabenazine for 9 years. During a hospital admission for an unrelated medical illness, she was given two doses of chlorpromazine 25 mg for a vascular headache and within hours became mute, extremely rigid, and unable to move or swallow. The consultation psychiatrist confirmed the diagnosis of severe drug-induced parkinsonism by intramuscular injection of benztropine mesylate which resulted in a dramatic immediate improvement. Both chlorpromazine and tetrabenazine were discontinued and the patient's severe parkinsonian symptoms completely abated on oral benztropine mesylate. Tetrabenazine alone, was restarted after 48 hours to control her Huntington's Chorea and there was no recurrence of parkinsonism. (Past history revealed the patient to have tolerated the same doses of chlorpromazine and tetrabenazine when given separately.) Previous literature reports concurrent safe use of antipsychotics with tetrabenazine, but this case report would suggest caution, and early discontinuance in the event of parkinsonism.