Psychiatry for USMLE Step 2 CK

A 24-year-old man brought in by police is agitated, diaphoretic and hypertensive with a temperature of 39.4°C. He is on fluoxetine and was given tramadol in the emergency department 2 hours ago. Examination shows hyperreflexia and inducible ankle clonus, worse in the lower limbs. What is the most likely diagnosis?

1. Serotonin syndrome correct Correct. Onset within hours of adding a serotonergic drug, with autonomic instability, altered mental state and NEUROMUSCULAR HYPERACTIVITY. Clonus and hyperreflexia greater in the legs is close to diagnostic, and tramadol plus an SSRI is a common precipitant.
2. Anticholinergic toxicity Gives dry skin and dry mucous membranes with absent bowel sounds. This patient is diaphoretic, and bowel sounds are typically normal or increased in serotonin syndrome.
3. Malignant hyperthermia Triggered by volatile anesthetics or succinylcholine intraoperatively, with masseter spasm and a rapidly rising end-tidal CO₂.
4. Neuroleptic malignant syndrome Follows dopamine antagonists, develops over days rather than hours, and produces lead-pipe RIGIDITY with hyporeflexia, the opposite neuromuscular picture.
5. Sympathomimetic intoxication Plausible on vital signs alone, but stimulant toxicity does not produce clonus and lower-limb-predominant hyperreflexia, and the drug history points at serotonin excess.

The point: Serotonin syndrome: hours, clonus, hyperreflexia, diaphoresis. NMS: days, rigidity, hyporeflexia, dopamine blocker. Cool, give benzodiazepines, stop the agent; cyproheptadine for refractory cases.

Source: USMLE Content Outline — psychiatry and pharmacotherapy NBME / FSMB (USMLE programme) · tier 0, exam blueprint / regulator