Acute dystonia in a 22-year-old man after haloperidol

A 22-year-old man with a known history of schizophrenia presented to the emergency department with acute agitation, disorganised speech and thought disorder. His regular medications were risperidone 3 mg daily (stable for six months) and diphenhydramine 25 mg at night for insomnia. He had no known allergies. At 10:00, he was given a single intramuscular injection of haloperidol 5 mg and lorazepam 2 mg for agitation. At 12:15, approximately two hours later, he developed sudden twisting of his neck to the left and upward deviation of his eyes, and he was in significant pain and distress. On examination, he was alert and oriented, with sustained involuntary contraction of cervical muscles and upward gaze deviation. Pupils were normal. Temperature was 36.9°C, pulse 100 beats/min, blood pressure 140/85 mmHg, respiratory rate 18 breaths/min, and oxygen saturation 98%. The rest of the neurological examination was unremarkable. Laboratory tests including full blood count, electrolytes, glucose, calcium, and magnesium were within normal limits. A 12-lead ECG showed a corrected QT interval of 480 ms, which was not present on a previous ECG, but this was not associated with symptoms. The dystonic reaction was treated with a single intravenous dose of diphenhydramine 50 mg, which resulted in rapid resolution of the neck twisting and eye deviation within 15 minutes. He was observed for a further hour with no recurrence. No rechallenge with haloperidol was performed. His regular risperidone and diphenhydramine were continued as planned. The reaction was attributed to the administered haloperidol, and he was advised to avoid typical antipsychotics in the future.