Acute Dystonic Stiff Neck from Antipsychotics
Administer benztropine 1–2 mg intramuscularly or intravenously immediately, which will provide rapid relief within minutes. 1, 2
Immediate Treatment
First-line therapy is benztropine 1–2 mg IM or IV, which produces symptom resolution within minutes and is the preferred anticholinergic agent for acute dystonia. 1, 2
Diphenhydramine 25–50 mg IM or IV is an equally effective alternative when benztropine is unavailable or contraindicated. 1, 2
Critical Safety Consideration
Assess immediately for laryngeal involvement by asking about choking sensation, breathing difficulty, or stridor—laryngeal dystonia is a life-threatening emergency requiring urgent anticholinergic treatment to prevent respiratory compromise and fatal outcomes. 1, 2 When administering benztropine with other sedating agents, monitor oxygen saturation and respiratory effort closely for respiratory depression. 1
Route of Administration
The intramuscular route is preferred over intravenous for emergency administration in this setting. 2
Post-Acute Management
After resolving the acute dystonic reaction, reassess the antipsychotic regimen:
- Consider dose reduction of the current antipsychotic if clinically feasible. 3
- Switch to an atypical antipsychotic with lower D2 receptor affinity if continued antipsychotic therapy is necessary, as atypical agents carry substantially lower risk of extrapyramidal symptoms. 3, 4
- Do not continue the same dose of the offending antipsychotic without modification, as this leads to recurrence. 1
Prevention for High-Risk Patients
Prophylactic anticholinergic agents should be considered for patients at highest risk: young males receiving high-potency dopamine D2 antagonists (e.g., haloperidol, fluphenazine). 1, 2 Young age is the single most significant risk factor, with male sex further increasing susceptibility. 1, 5
Prophylaxis is particularly important when medication adherence is a concern, as dystonic reactions are extremely distressing and represent a common reason for treatment discontinuation. 1, 2
Reassess the need for prophylactic anticholinergics after the acute treatment phase or when antipsychotic doses are reduced—many patients no longer require prophylaxis during long-term maintenance therapy. 2
Mechanism and Timing
Acute dystonia results from sudden, non-selective blockade of dopamine D2 receptors in the nigrostriatal pathway, creating relative cholinergic excess. 1, 6 Symptoms typically manifest within the first few days to weeks after initiating or substantially increasing the dose of a dopamine-blocking medication. 1, 5, 7
Anticholinergic agents are highly effective because they suppress the widespread influence of tonically active striatal cholinergic interneurons that become disinhibited when dopaminergic tone is blocked. 1, 6
Contraindications to Anticholinergics
Avoid anticholinergic agents in patients with glaucoma, benign prostatic hypertrophy, or current anticholinergic drug intoxication, as these conditions heighten the risk of adverse effects. 1
Differential Diagnosis
Distinguish acute dystonia from akathisia, which presents with subjective restlessness, pacing, and inability to sit still rather than sustained muscle contractions. 2, 3 Anticholinergic agents are not consistently effective for akathisia, which responds better to lipophilic beta-blockers such as propranolol. 2, 3, 4
Do not confuse with tardive dyskinesia, which develops after long-term antipsychotic exposure (not days to weeks), presents with involuntary rhythmic orofacial movements rather than sustained muscle spasms, and does not respond to anticholinergics. 3, 8