Acute dystonic reaction to haloperidol
The case
A 25-year-old man with schizophrenia was started on haloperidol 5 mg twice daily 3 days ago. He presents to the emergency department with 2 hours of severe neck pain and an inability to straighten his head, which he says is 'locked to the left'. There is torticollis with sternocleidomastoid contraction, trismus and upward deviation of the eyes. He is afebrile, haemodynamically stable, alert and oriented, with no tremor, bradykinesia or autonomic instability. A recent urine drug screen is negative. What is the most appropriate immediate management?
Options
- AIntramuscular benztropine 1 to 2 mg
- BUrgent CT head
- CIntravenous diazepam 10 mg
- DReduce the haloperidol dose and observe
- ESwitch to oral olanzapine 5 mg daily
Think it through before you read on. Which single option is best, and why are the other four wrong?
Show the answer and explanation
Answer
A. Intramuscular benztropine 1 to 2 mg
Why this is the right answer
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.
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.
Why the other options are wrong
- B
The history is diagnostic; imaging delays a treatment that works in minutes.
- C
Benzodiazepines are second-line adjuncts; they are slower and less reliable than an anticholinergic.
- D
Dose reduction does not relieve an established dystonia and leaves the patient in pain with a risk of airway involvement.
- E
Switching drugs is a longer-term decision; the acute contraction must be reversed first.
High-yield takeaway
Torticollis, trismus or oculogyric crisis within days of a dopamine blocker is acute dystonia: give benztropine 1 to 2 mg IM/IV and it resolves in minutes.
Reference: Therapeutic Guidelines: Psychotropic, Antipsychotic adverse effects (extrapyramidal) (2021)
Common questions
Which drugs commonly cause acute dystonia?
High-potency antipsychotics such as haloperidol, and antiemetics such as metoclopramide and prochlorperazine.
How is acute dystonia different from neuroleptic malignant syndrome?
Dystonia is focal, painful and afebrile with a clear sensorium. Neuroleptic malignant syndrome causes fever, generalised rigidity, autonomic instability and a raised creatine kinase.
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