Acute dystonic reaction to methotrimeprazine in hypoparathyroidism

To report a case of acute dystonic reaction to methotrimeprazine in a patient with untreated hypoparathyroidism, emphasizing the potential increased sensitivity of hypocalcemic patients to the extrapyramidal adverse effects of antipsychotic drugs.

An 80-year-old man who had untreated hypoparathyroidism and chronic hypocalcemia 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 methotrimeprazine several years earlier. The patient denied having any other diseases or taking any other medications. After 4 days, the disorientation, psychomotor restlessness, dystonic grimacing, protrusion of the tongue, and speech difficulties disappeared, despite a remaining low serum calcium concentration.

A possible mechanism, by which striatal calmodulin-mediated adenylate cyclase activation is inhibited by the combined effects of phenothiazines and hypocalcemia, is discussed.

In this patient, it is not possible to ascertain whether the dystonic reaction was due to hypocalcemia, phenothiazine administration, or both. However, it is suggested that patients with hypocalcemia may be sensitive to the extrapyramidal adverse effects of antipsychotics. In addition, acute unexpected dystonic reactions to a small dose of antipsychotics warrants measurement of the patient's serum calcium concentration.