Assess for neuroleptic malignant syndrome, as the tetrad of rigidity, hyperthermia, autonomic instability, and elevated CK after recent antipsychotic initiation requires immediate discontinuation and emergency medical transfer.

The clinical tetrad — rigidity, hyperthermia, autonomic instability, and altered mental status — with a markedly elevated CK (reflecting severe rhabdomyolysis) within days of antipsychotic initiation is NMS. Mortality rates are significant if untreated. Immediate actions: discontinue the antipsychotic, provide aggressive supportive care (cooling, IV hydration, renal protection from myoglobin), and consider dantrolene (for rigidity) or bromocriptine (dopamine agonist). This patient needs ICU-level medical management.

Assess for acute dystonia and administer benztropine, as the severe muscle rigidity occurring within days of antipsychotic initiation is consistent with an acute extrapyramidal reaction requiring anticholinergic treatment.

Acute dystonia presents with focal muscle spasm (torticollis, oculogyric crisis), not generalized rigidity with fever and autonomic instability. This presentation far exceeds dystonia.

Obtain a urine drug screen to rule out sympathomimetic intoxication, as stimulant use or serotonergic substance ingestion could produce this clinical picture independent of the antipsychotic medication.

While serotonin syndrome and sympathomimetic toxicity share some features, the clinical context (new antipsychotic, lead-pipe rigidity, markedly elevated CK) is diagnostic of NMS. A UDS would not change the immediate management.

Reduce the antipsychotic dose by half and monitor closely over the next 24 hours, as the symptoms may represent a dose-related extrapyramidal effect that will improve with conservative dose adjustment.

NMS requires complete antipsychotic discontinuation, not dose reduction. Continuing any dose risks progression and death. This is a medical emergency, not a dose-adjustment scenario.