Associated with adverse drug interactions - movement disorders

Red flags

Rigidity + fever + autonomic instability + altered consciousness - NMS
Trismus, torticollis, oculogyric crisis in a young patient after antiemetic/antipsychotic - acute dystonia (airway risk if laryngeal)
Hyperreflexia + clonus + fever + agitation - serotonin syndrome
Sudden severe rigidity with hyperthermia - consider malignant hyperthermia (anaesthetic trigger) as a differential

Acute dystonia (hours-days after exposure)

Antipsychotics (esp. high-potency typicals - haloperidol), metoclopramide, prochlorperazine
Young, male, antipsychotic-naive at highest risk

Akathisia

Antipsychotics, metoclopramide, SSRIs - subjective inner restlessness, often mistaken for anxiety/agitated psychosis (worsening with more antipsychotic)

Parkinsonism (drug-induced)

Antipsychotics (esp. typicals), metoclopramide, sodium valproate, some calcium channel blockers (flunarizine)
Symmetric, resolves over weeks-months after cessation

Tardive dyskinesia

Chronic antipsychotic exposure - orofacial, choreoathetoid movements; may persist after cessation

NMS vs serotonin syndrome (distinguish by exam)

Feature	NMS	Serotonin syndrome
Onset	Days	Hours
Tone	Lead-pipe rigidity	Hyperreflexia, clonus
Reflexes	Reduced	Increased
Cause	Dopamine antagonist / agonist withdrawal	Serotonergic drug combination

Tremor

Recent antipsychotic/antiemetic start or dose increase
Serotonergic drug combinations (SSRI/SNRI + MAOI, tramadol, linezolid)
Time course - hours (dystonia, serotonin syndrome) vs days (NMS) vs months-years (tardive dyskinesia)
Recent abrupt dopaminergic drug withdrawal (Parkinson's medication) - can mimic NMS

Tone (lead-pipe vs normal), reflexes, clonus
Temperature, autonomic signs (BP, HR, diaphoresis)
Movement pattern - dystonic posturing vs choreoathetoid vs tremor vs restlessness

Acute dystonia: IV/IM anticholinergic (benztropine) or antihistamine (diphenhydramine) - rapid response
NMS: stop the causative drug, supportive care/cooling, dantrolene or bromocriptine for severe cases, benzodiazepines for agitation
Serotonin syndrome: stop causative drug(s), benzodiazepines, cyproheptadine if moderate-severe, active cooling
Akathisia: dose reduction/cessation, beta-blocker (propranolol) or benzodiazepine; switching antipsychotic
Tardive dyskinesia: cease/reduce causative agent where possible, valbenazine/tetrabenazine if persistent and disabling

Akathisia is easily mistaken for worsening psychiatric agitation, prompting more antipsychotic - the wrong response
NMS can occur with any dopamine antagonist, not just antipsychotics (also metoclopramide), and with abrupt levodopa withdrawal
Tardive dyskinesia may not resolve on stopping the drug and can even transiently worsen
Serotonin syndrome and NMS are distinguished clinically (reflexes/tone), not by a lab test

1. Time course narrows it fast

"Hours points to dystonia or serotonin syndrome, days to NMS, months to tardive dyskinesia."

2. Reflexes separate the two big mimickers

"Increased reflexes and clonus is serotonin syndrome; reduced reflexes with lead-pipe rigidity is NMS."

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