Which clinical feature best distinguishes tardive dyskinesia from acute dystonia as an antipsychotic side effect?

Explanation

## Distinguishing Tardive Dyskinesia from Acute Dystonia ### Key Clinical Differences **Key Point:** Tardive dyskinesia (TD) and acute dystonia are both extrapyramidal side effects of antipsychotics, but they differ fundamentally in onset, duration, reversibility, and response to treatment. | Feature | Acute Dystonia | Tardive Dyskinesia | |---------|----------------|-------------------| | **Onset** | Hours to days after drug start or dose ↑ | Months to years of continuous use | | **Duration** | Minutes to hours (episodic) | Persistent; may outlast drug discontinuation | | **Movement pattern** | Sustained muscle contractions, twisting | Involuntary choreiform, athetoid, orofacial movements | | **Reversibility** | Fully reversible with anticholinergics | Often irreversible even after drug cessation | | **Anticholinergic response** | Dramatic, immediate relief | No response; may worsen | | **Risk factors** | Young age, high-potency typical APs | Older age, female, long duration of use | ### Why Option 1 (Tardive Dyskinesia) is Correct **High-Yield:** Tardive dyskinesia is characterized by **involuntary orofacial movements** (lip smacking, tongue protrusion, grimacing) and **choreiform limb movements** that emerge after **months to years** of antipsychotic exposure. This temporal and phenomenological profile is the gold-standard discriminator. ### Pathophysiology **Clinical Pearl:** Acute dystonia results from acute dopamine blockade causing relative cholinergic excess in the basal ganglia, explaining rapid anticholinergic response. Tardive dyskinesia is thought to arise from dopamine receptor supersensitivity and neuroadaptation after chronic blockade — hence anticholinergics are ineffective and may paradoxically worsen it. ### Clinical Implications 1. **Prevention:** Minimize antipsychotic duration and dose; use second-generation agents when possible (lower TD risk). 2. **Management of TD:** Reduce or discontinue offending agent; consider tetrabenazine or valbenazine (VMAT2 inhibitors). 3. **Management of acute dystonia:** Immediate IM/IV benztropine or diphenhydramine. [cite:Stahl's Essential Psychopharmacology 6e Ch 11]