We report a 63-year-old man who presented with
amoxapine-induced
tardive dystonia. At 49 years of age, he developed depression and was administrated 50 mg
amoxapine, 4 mg cloxazoram and 3 mg
biperiden per day. The daily dose of
amoxapine was gradually increased up to 150 mg at 58 years of age.
At 61 years of age and after having been taking
amoxapine for twelve years, he noticed a rotating left arm and
muscle pain in his left shoulder and arm while walking. At 62 years of age, he stopped taking these three drugs. However, the dystonic movements and
pain both continued to get worse. Neurological findings revealed no abnormality except for a dystonic posture and movements in the neck and bilateral arms while sitting, standing and walking. Positron emission tomography with C-11
raclopride revealed a mild decrease in the
dopamine D 2 receptor numbers in the bilateral striatum. However, two
dopamine agonists,
pergolide and
bromocriptine, worsened his
dystonia. In contrast, the daily administration of 2 mg of
trihexyphenidyl, an
anti-cholinergic agent, markedly ameliorated the
dystonia symptoms. As a result, the long-term co-administration of
biperiden, an
anti-cholinergic agent, may mask the toxicity of
amoxapine, which may induce
tardive dystonia.