## Diagnosis: Neuroleptic Malignant Syndrome (NMS) ### Clinical Presentation & Diagnostic Criteria **Key Point:** NMS is a life-threatening idiosyncratic reaction to antipsychotics (especially high-potency typical agents like haloperidol). It is characterized by the **classic tetrad: fever, rigidity, altered mental status, and autonomic instability**, typically developing **24–72 hours** after antipsychotic exposure or dose increase. ### Why This Is NMS, Not Serotonin Syndrome | Feature | NMS | Serotonin Syndrome | |---------|-----|--------------------| | **Antipsychotic exposure** | Yes (haloperidol ×2 years, then ↑ dose) | No | | **Onset timeline** | 24–72 hours | Hours (4–12) | | **Rigidity type** | Lead-pipe (uniform) | Mild-moderate, variable | | **Clonus** | Absent | Present (spontaneous/inducible) | | **CK elevation** | Severe (often >1000, can be >10,000) | Mild-moderate | | **Rhabdomyolysis** | Common, severe | Less common | | **Myoglobinuria** | Yes (dark urine) | Rare | This patient has **severe NMS** with: - Antipsychotic exposure (haloperidol dose doubled 18 hours ago) - Fever 39.5°C - Lead-pipe rigidity (described as "severe") - Altered mental status - Markedly elevated CK (8500 U/L) → **severe rhabdomyolysis** - Dark urine → **myoglobinuria** - Acute kidney injury (Cr 2.1 from 0.9) ### Immediate Management Algorithm ```mermaid flowchart TD A[Suspected NMS]:::outcome --> B[STOP antipsychotic immediately]:::urgent B --> C[Assess severity]:::decision C -->|Mild| D[Supportive care, benzodiazepines]:::action C -->|Moderate-Severe| E[ICU admission]:::urgent E --> F[Aggressive IV hydration]:::action F --> G[Target urine output 200-300 mL/hr]:::action G --> H[Dantrolene 1 mg/kg IV q4-6h]:::action H --> I[Cooling measures]:::action I --> J[Monitor CK, creatinine, myoglobin]:::action J --> K[Dialysis if renal failure]:::action ``` **High-Yield:** The **immediate priority is to stop the antipsychotic** and prevent acute kidney injury from rhabdomyolysis by aggressive hydration. ### Pharmacological Management **Dantrolene Sodium:** - **Mechanism:** Inhibits calcium release from sarcoplasmic reticulum in skeletal muscle → reduces muscle rigidity and heat production - **Dosing:** 1 mg/kg IV push, repeat every 4–6 hours until symptoms resolve or max 10 mg/kg/day - **Efficacy:** Reduces mortality from ~11% to ~5% when used early - **Monitoring:** Watch for hepatotoxicity (LFTs), thrombophlebitis at IV site **Bromocriptine (dopamine agonist):** - Less evidence than dantrolene; can be used as adjunct - Dosing: 2.5–10 mg PO/NG three times daily - Onset slower than dantrolene **Benzodiazepines:** - Lorazepam 2–4 mg IV for agitation and muscle relaxation - Does NOT treat the underlying pathophysiology but provides symptomatic relief ### Fluid Management **Clinical Pearl:** Aggressive hydration is **critical** to prevent acute tubular necrosis from myoglobin precipitation in renal tubules. - Target urine output: **200–300 mL/hr** (use foley catheter) - IV fluid: Normal saline (avoid hypotonic fluids) - Consider **alkalinization of urine** (sodium bicarbonate) to increase myoglobin solubility (target urine pH >6.5) - Monitor: Serum creatinine, urine myoglobin, electrolytes (hyperkalemia risk from rhabdomyolysis) ### Prognosis & Recovery - **Mortality:** 5–15% if untreated; <5% with early recognition and dantrolene - **Recovery timeline:** 24–72 hours after stopping antipsychotic - **Rechallenging antipsychotics:** Wait ≥5–14 days; use low-potency or atypical agent (risperidone, olanzapine) at lowest effective dose; avoid high-potency typicals [cite:Harrison 21e Ch 395; Kaplan & Sadock's Synopsis of Psychiatry 11e] 
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.