We describe a rare case antithyroid drug induced hypothyroidism leading to an acute psychotic episode.

A 39 year old woman complaining of anxiety was referred to our day hospital unit in september 2010. Her symptoms began a month earlier and she denied any past personal or family history of psychiatric disorders except for an acute psychotic episode in august 2010. She diagnosed with hyperthyroidism in june 2010 and was started on medication with 30 mg of methilmazole. Two weeks later she started to feel confused, and she developed auditory and visual hallucinations as well as persecutory delusionsn and she was hospitalized in a psychiatric facility. Upon admittance lab work indicated severe hypothyroidism (TSH 87 uI/L)and high total cholesterol. Antythiroid medication was suspended and the patient was started on antipsychotic medication with 10 mg of haloperidol.

Four days later the patient dysplayed a complete remission of symtpoms. She self discontinuated the antipsychotic medication one week after discharge and showed no sign of psychotic symptoms. Thyroid function was later revaluated and indicated mild hypethyroidism, for which methilmazole 10 mg was prescribed. in october 2010 the patient was evaluated in our unit and showed no sign of psychotic symptoms or anxiety.

Although very few cases of methilmazole induced psychosis are reported, based on the patient's history, on the doses of medication that were prescribed, on the lab work and on the onset, evolution and remission of her symptoms we hypothesize that the psychotic episode was drug induced.