Neuroleptic malignant syndrome

Pathophysiology & Etiology - The Dopamine Drop

• Core Mechanism: Sudden, drastic ↓ in central dopamine (DA) activity, primarily from D2 receptor blockade.
• Primary Triggers:
  • Antipsychotics (Neuroleptics): High-potency typicals (e.g., Haloperidol) pose the highest risk.
  • Antiemetics: Metoclopramide, prochlorperazine.
  • Abrupt Withdrawal: Sudden cessation of DA agonists (e.g., Levodopa in Parkinson's disease).

⭐ NMS is an idiosyncratic reaction, not a true dose-dependent toxicity. It can occur at any point during therapy.

Clinical Presentation - The FEVER Pitch

• Onset is typically gradual, over 1-3 days after altering dopamine antagonist therapy.
• 📌 FEVER mnemonic outlines the core features:
  • Fever: Hallmark sign. Typically high, often >40°C (104°F).
  • Encephalopathy: Universal feature of altered mental status, from delirium to coma.
  • Vitals Instability: Autonomic dysfunction is common.
    • Tachycardia, labile BP, diaphoresis, tachypnea.
  • Enzymes Elevated: Reflects muscle breakdown.
    • ↑ Creatine Kinase (CK), often >1,000 IU/L.
    • Myoglobinuria, leukocytosis, elevated AST/ALT.
  • Rigidity: Severe, generalized "lead-pipe" muscle rigidity.

⭐ High-Yield: The rigidity in NMS is classically "lead-pipe" (diffuse, constant resistance), distinguishing it from the clonus and hyperreflexia more typical of Serotonin Syndrome.

Diagnosis & Differentials - NMS vs. The Impostors

• Diagnosis is clinical, based on history (exposure to dopamine antagonists) and characteristic symptoms. Key labs show marked elevation in Creatine Kinase (CK >1000 IU/L), leukocytosis, and metabolic acidosis.
• 📌 FEVER Mnemonic for NMS: Fever, Encephalopathy, Vitals unstable, Elevated enzymes (CK), Rigidity of muscles.

Management - Cooling & Counteracting

• Immediate Cooling: Aggressive external and internal methods.
  • Ice packs (axilla, groin), cooling blankets, misting.
  • Consider chilled IV fluids or gastric lavage.
• Pharmacologic Counteraction:
  • Dantrolene: Direct muscle relaxant; inhibits Ca²⁺ release from sarcoplasmic reticulum.
  • Bromocriptine: Dopamine (D₂) agonist to reverse central hypo-dopaminergic state.
  • Benzodiazepines (e.g., lorazepam) for agitation.

⭐ Dantrolene is crucial for treating rigidity and hyperthermia in NMS, but bromocriptine is specifically added to address the underlying central dopamine receptor blockade that precipitates the syndrome.

High‑Yield Points - ⚡ Biggest Takeaways

• A life-threatening reaction to neuroleptic agents, especially high-potency typical antipsychotics.
• Classic tetrad: hyperthermia, autonomic instability, "lead-pipe" muscle rigidity, and altered mental status.
• The underlying cause is central D2 receptor blockade.
• Look for a markedly elevated creatine kinase (CK) from rhabdomyolysis.
• Treatment requires immediate cessation of the drug, supportive care, and dantrolene or bromocriptine.
• Key differentiator from serotonin syndrome is bradykinesia and extreme rigidity.