A 28-year-old male on risperidone for 2 weeks presents with fever (39.8°C), diaphoresis, severe muscle rigidity, and a CK of 12,000 U/L. He is confused and his BP oscillates widely. Urine is dark. Which investigation is most likely to show a diagnostic finding?

• A Serum iron levels (low iron supports NMS) ✓
• B Urine myoglobin (elevated, confirming rhabdomyolysis)
• C EEG (periodic discharges in NMS)
• D Lumbar puncture (lymphocytic pleocytosis in NMS)

Explanation

Neuroleptic Malignant Syndrome (NMS) is associated with low serum iron levels, which is a consistent and diagnostically supportive laboratory finding. The clinical scenario is classic NMS: hyperthermia, lead-pipe rigidity, autonomic instability, and elevated CK. While rhabdomyolysis does occur (elevated myoglobin, dark urine, elevated CK), low serum iron is a more specific supportive marker for NMS distinct from other causes of rhabdomyolysis. EEG and LP findings are non-specific in NMS.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.