A 48-year-old man with schizophrenia on haloperidol 15 mg daily for 3 weeks presents with high fever (40.2°C), severe muscle rigidity, altered mental status, and autonomic instability (BP 160/100 mmHg, HR 118/min). Serum creatine kinase is 2800 IU/L. The patient is conscious and breathing spontaneously. What is the most appropriate immediate next step in management?

Explanation

## Clinical Presentation: Neuroleptic Malignant Syndrome (NMS) This patient meets **all four cardinal features of NMS**: 1. **Fever** (≥38.5°C) — 40.2°C 2. **Muscle rigidity** — "severe muscle rigidity" 3. **Altered mental status** — confusion/altered consciousness 4. **Autonomic instability** — hypertension, tachycardia **High-Yield:** NMS is a **medical emergency** with mortality 10–20% if untreated. The temporal relationship (3 weeks on haloperidol) and elevated CK (2800 IU/L, indicating rhabdomyolysis) confirm the diagnosis. ## Diagnostic Criteria & Severity Assessment **Key Point:** NMS diagnosis is **clinical**; no single lab test confirms it. However, elevated CK (often >1000 IU/L) and myoglobinuria are hallmarks of rhabdomyolysis. ```mermaid flowchart TD A[Suspected NMS: Fever + Rigidity + Altered MS + Autonomic Instability]:::outcome --> B{Confirmed NMS?}:::decision B -->|Yes| C[STOP antipsychotic IMMEDIATELY]:::urgent C --> D[Initiate dantrolene 2.5 mg/kg IV q5-10min]:::action D --> E[Aggressive cooling: ice packs, cooling blankets, cold IV saline]:::action E --> F[IV hydration: target UOP 200-300 mL/hr]:::action F --> G[Monitor: CK, myoglobin, renal function, electrolytes]:::action G --> H{Rhabdomyolysis with AKI?}:::decision H -->|Yes| I[Urine alkalinization + aggressive hydration]:::action H -->|No| J[Supportive care + ICU monitoring]:::action I --> K[Benzodiazepines for agitation/seizure prophylaxis]:::action J --> K ``` ## Management of NMS: Step-by-Step ### 1. **Discontinue Antipsychotic (IMMEDIATELY)** - This is the **single most important intervention** - Continuing the offending agent is contraindicated and worsens outcomes - Recovery typically begins within 24–72 hours of discontinuation ### 2. **Dantrolene Sodium (Specific Pharmacotherapy)** **Key Point:** Dantrolene is the **only specific agent** for NMS. It works by: - Inhibiting calcium release from the sarcoplasmic reticulum in skeletal muscle - Reducing muscle rigidity and heat production - Dose: 2.5 mg/kg IV push every 5–10 minutes until: - Rigidity resolves, OR - Temperature normalizes, OR - Maximum cumulative dose of 10 mg/kg is reached **Clinical Pearl:** Dantrolene must be reconstituted with sterile water (no saline) and given IV. Oral dantrolene is used for maintenance after acute crisis. ### 3. **Aggressive Cooling** - Ice packs to groin, axillae, neck - Cooling blankets - Cold IV saline infusion - Target: core temperature <38.5°C ### 4. **IV Hydration & Rhabdomyolysis Management** - **Aggressive IV hydration:** 1–2 L/hour normal saline - Target urine output: **200–300 mL/hr** - Monitor for myoglobinuria (dark/cola-colored urine) - If myoglobinuria present: **urine alkalinization** (sodium bicarbonate) to pH >6.5 to prevent myoglobin precipitation in renal tubules ### 5. **Supportive Care** - ICU admission for continuous monitoring - Benzodiazepines (lorazepam) for agitation, seizure prophylaxis - Treat electrolyte abnormalities - Monitor for acute kidney injury ## Comparison: NMS vs. Serotonin Syndrome | Feature | NMS | Serotonin Syndrome | |---------|-----|--------------------| | **Trigger** | Antipsychotics (dopamine antagonists) | Serotonergic drugs (SSRI, MAOI, tramadol) | | **Onset** | Days to weeks | Hours to days | | **Muscle tone** | Lead-pipe rigidity (uniform) | Normal or hyperreflexia | | **Clonus** | Absent | Present (especially lower limbs) | | **GI** | Constipation | Diarrhea | | **First-line Rx** | Dantrolene + supportive care | Supportive care + cyproheptadine (severe) | | **Mortality** | 10–20% untreated | <5% with supportive care | **Warning:** Do NOT give dantrolene for serotonin syndrome. Do NOT continue antipsychotics in NMS. ## Why Each Option Is Right or Wrong **Correct Answer (Option 1 - Dantrolene):** - Addresses the underlying pathophysiology (muscle calcium release) - Only specific pharmacotherapy for NMS - Must be combined with discontinuation of haloperidol and aggressive supportive care - Improves survival and reduces complications [cite:Harrison 21e Ch 449; Adityanjee et al. Neuroleptic malignant syndrome in the "atypical" antipsychotic era: diagnostic and management challenges. J Clin Psychiatry. 2005;66(3):273-282.]