Acute dystonic reaction to haloperidol

This is an acute dystonic reaction. Dystonia is a sustained, painful muscle contraction, and the classic forms after antipsychotics are torticollis (neck), trismus (jaw), oculogyric crisis (eyes rolled upward) and, rarely, laryngeal dystonia, which can obstruct the airway. It appears within hours to a few days of starting or increasing a dopamine-blocking drug. High-potency first-generation antipsychotics such as haloperidol are the commonest cause; metoclopramide and prochlorperazine also do it. Young men are at highest risk.

The mechanism is an imbalance between dopamine and acetylcholine in the basal ganglia. Blocking dopamine leaves cholinergic activity unopposed, and the treatment is an anticholinergic. Benztropine 1 to 2 mg intramuscularly or intravenously relieves symptoms within 10 to 30 minutes; the dose can be repeated if needed. Therapeutic Guidelines (Psychotropic) lists benztropine as first-line, with promethazine or diphenhydramine as alternatives [VERIFY].

After the acute episode, oral benztropine is usually continued for a few days because haloperidol has a long half-life and the dystonia can recur. Longer term, the antipsychotic dose is reduced or the drug is changed to a second-generation agent with a lower risk of extrapyramidal effects.

It is important to separate dystonia from neuroleptic malignant syndrome, which causes fever, lead-pipe rigidity of all muscles, autonomic instability and raised creatine kinase, and is a medical emergency needing drug cessation and supportive care. This man is afebrile, alert and stable, with focal rather than generalised rigidity.

Dystonia is frightening and painful. Reassurance that it will pass quickly with treatment is part of the management.