ACUTE DYSTONIC REACTION TO METHOTRIMEPRAZINE IN HYPOPARATHYROIDISM

OBJECTIVE: TO report a case of acute dystonic reaction to methotrimepr azine in a patient with untreated hypoparathyroidism, emphasizing the potential increased sensitivity of hypocalcemic patients to the extrap yramidal adverse effects of antipsychotic drugs. CASE SUMMARY: An 80-y ear-old man who had untreated hypoparathyroidism and chronic hypocalce mia developed an acute dystonic reaction 20 minutes after ingestion of methotrimeprazine 25 mg. His medical history included an ill-defined psychiatric disorder for which he had been treated with methotrimepraz ine several years earlier, The patient denied having any other disease s or taking any other medications, After 4 days, the disorientation, p sychomotor restlessness, dystonic grimacing, protrusion of the tongue, and speech difficulties disappeared, despite a remaining low serum ca lcium concentration. DISCUSSION: A possible mechanism, by which striat al calmodulin-mediated adenylate cyclase activation is inhibited by th e combined effects of phenothiazines and hypocalcemia, is discussed. C ONCLUSIONs: In this patient, it is not possible to ascertain whether t he dystonic reaction was due to hypocalcemia, phenothiazine administra tion, or both, However, it is suggested that patients with hypocalcemi a may be sensitive to the extrapyramidal adverse effects of antipsycho tics. In addition, acute unexpected dystonic reactions to a small dose of antipsychotics warrants measurement of the patient's serum calcium concentration.