Snapshot A 34-year-old woman is brought to the emergency department by her husband due to an altered mental status. The husband reports that his wife has schizophrenia, and she recently had a change in dosage to her antipsychotic medication. Her temperature is 103°F (39.4°C), labile blood pressure, pulse is 105/min, and respirations are 26/min. She appears profusely diaphoretic and has muscle rigidity in her extremities. In addition to supportive care, she is started on dantrolene. Introduction Mechanism of action blocks ryanodine receptors decreases excitation-contraction coupling decreases Ca2+ release from the sarcoplasmic reticulum in skeletal muscle Clinical use malignant hyperthermia hypermetabolic crisis secondary to inhaled anesthetic use (e.g., halothane) or succinylcholine patients have a genetic abnormality in ryanodine or dihydropyridine receptors, a skeletal muscle protein results in excessive Ca2+ release from the sarcoplasmic reticulum neuroleptic malignant syndrome (NMS) medical emergency secondary to neuroleptic use (e.g., antipsychotics) characterized by hyperthermia mental status change rigidity autonomic dysfunction