Which clinical feature best distinguishes typical antipsychotic-induced tardive dyskinesia from acute dystonia?

Explanation

## Distinguishing Tardive Dyskinesia from Acute Dystonia **Key Point:** Tardive dyskinesia (TD) and acute dystonia are both extrapyramidal side effects of antipsychotics, but they differ fundamentally in timing, mechanism, and reversibility. ### Temporal Onset and Duration | Feature | Acute Dystonia | Tardive Dyskinesia | |---------|---|---| | **Onset** | Hours to days after drug start (or dose ↑) | Months to years of continuous exposure | | **Duration** | Minutes to hours; resolves with anticholinergic | Persists; may be irreversible even after drug withdrawal | | **Mechanism** | Acute dopamine blockade → cholinergic excess | Chronic dopamine blockade → receptor supersensitivity | ### Clinical Presentation **Acute Dystonia:** - Sustained muscle contractions (torticollis, oculogyric crisis, opisthotonus) - Rapid onset, dramatic presentation - Responds dramatically to IM/IV benztropine within 5–15 minutes **Tardive Dyskinesia:** - Involuntary choreiform, athetoid, or rhythmic movements - Orofacial region (lip smacking, tongue protrusion, grimacing) - Limbs (finger movements, restlessness) - Does NOT respond to anticholinergics; may worsen **High-Yield:** The **months-to-years latency** and **involuntary dyskinetic movements** are the cardinal discriminators. Acute dystonia is an emergency; TD is a chronic complication. **Clinical Pearl:** Anticholinergic challenge can help differentiate: acute dystonia improves; TD worsens or remains unchanged. **Mnemonic:** **TARDIVE** = **T**ime (years), **A**nticholinergics ineffective, **R**eceptor supersensitivity, **D**yskinesia (involuntary), **I**rreversible (often), **V**ery late onset, **E**xtrapyramidal. ### Why Option 1 Is Correct Tardive dyskinesia is defined by: 1. Exposure to dopamine antagonists for ≥3 months (typically years) 2. Involuntary orofacial and limb movements (choreiform, athetoid, or rhythmic) 3. Emergence after prolonged treatment, not acutely This temporal and phenomenological profile uniquely identifies TD among extrapyramidal syndromes.