Neuroleptic Malignant Syndrome

NMS: Intro & Causes - The Dopey Danger

• Neuroleptic Malignant Syndrome (NMS): Rare, life-threatening idiosyncratic reaction to dopamine D2 antagonists.
• Incidence: 0.02-3% with antipsychotics.
• Primary Causes:
  • Antipsychotics (most common):
    • Typical (e.g., Haloperidol) > Atypical (e.g., Risperidone).
  • Other dopamine antagonists: Metoclopramide.
  • Withdrawal of dopaminergic drugs (e.g., Levodopa).

⭐ NMS is idiosyncratic. Not strictly dose-dependent for occurrence, but higher doses/rapid escalation of causative agents can ↑ risk.

NMS: Pathophysiology - Dopamine Drain Drama

• Primary Insult: Central D2 receptor blockade.
  • Hypothalamus: Disrupts thermoregulation (fever), alters muscle tone.
  • Nigrostriatal Pathway: Blockade → severe muscle rigidity.
  • Mesolimbic Pathway: Blockade → altered mental status.
• Compounding Factor: Sympathetic hyperactivity contributes to autonomic instability (e.g., tachycardia, labile BP).

⭐ Abrupt withdrawal of dopaminergic agents (e.g., levodopa in Parkinson's) can also precipitate an NMS-like syndrome.

NMS: Clinical Features - Feverish & Stiff

Presents with a characteristic tetrad, often recalled by 📌 FEVER:

• Fever: Temperature typically >38°C (100.4°F), can be very high.
• Encephalopathy: Altered mental status ranging from confusion/agitation to delirium/coma.
• Vital sign instability: Autonomic dysfunction (tachycardia, labile BP, tachypnea, diaphoresis).
• Enzymes elevated: Marked ↑CK (often >1000 IU/L), leukocytosis, ↑myoglobin.
• Rigidity: Severe, generalized "lead-pipe" muscle rigidity.

⭐ 'Lead-pipe rigidity' is a classic, highly characteristic sign of NMS.

NMS: Diagnosis & DDx - Spotting the Syndrome

• Diagnosis of Exclusion: NMS is a diagnosis of exclusion; rule out other causes.
• Key Investigations:
  • CBC (leukocytosis), LFTs, RFTs, electrolytes, ABG.
  • Serum CK (markedly ↑, often >1000 IU/L), urine myoglobin.
  • CSF analysis: often normal; helps rule out CNS infection.
• Diagnostic Criteria: Apply established criteria (e.g., Levenson's: major + minor).
• Differential Diagnosis (DDx):
  • Serotonin Syndrome (key: hyperreflexia, myoclonus)
  • Malignant Hyperthermia (anaesthetic trigger)
  • Heat Stroke (environmental, dry skin)
  • CNS Infections (meningitis/encephalitis)
  • Catatonia, Lethal Catatonia

⭐ Markedly elevated Creatine Kinase (CK), often >1000 IU/L, is a hallmark laboratory finding in NMS.

NMS: Management - Cooling & Control

• Immediate Actions:
  • Stop ALL antipsychotics.
  • Maintain ABCs (Airway, Breathing, Circulation).
• Supportive Care:
  • Aggressive IV hydration.
  • Cooling measures (e.g., ice packs, cooling blankets).
• Pharmacological Therapy:
  • Dantrolene: 1-2.5 mg/kg IV (direct-acting muscle relaxant).
  • Bromocriptine: 2.5-10 mg TID (dopamine agonist).
  • Benzodiazepines (e.g., Lorazepam): For agitation, seizures, or rigidity.
• Refractory Cases:
  • Electroconvulsive Therapy (ECT).

⭐ Re-challenge with antipsychotics after NMS should be done cautiously, preferably with a low-potency atypical agent after at least 2 weeks.

NMS: Complications & Prognosis - Risky Aftermath

• Major Complications:
  • Rhabdomyolysis → myoglobinuria → Acute Renal Failure (ARF)
  • Disseminated Intravascular Coagulation (DIC)
  • Acute Respiratory Distress Syndrome (ARDS)
  • Seizures, Arrhythmias
  • Hepatic failure, Sepsis
• Prognosis:
  • Mortality: Historically 10-20%, significantly ↓ with prompt treatment.
  • Recovery: Full recovery can take days to weeks.

⭐ Acute kidney injury secondary to rhabdomyolysis is a major cause of morbidity and mortality in NMS.

High‑Yield Points - ⚡ Biggest Takeaways

• Life-threatening reaction to antipsychotics (especially high-potency first-generation), primarily due to D2 receptor blockade.
• Cardinal tetrad: Fever (hyperthermia), Encephalopathy (altered mental status), Vitals unstable (autonomic dysfunction), and Rigidity ("lead-pipe").
• Markedly ↑CK (often >1000 IU/L), ↑WBC (leukocytosis), and myoglobinuria are characteristic lab findings.
• Stop offending drug immediately; provide intensive supportive care (cooling, hydration).
• Specific pharmacological agents include dantrolene (muscle relaxant) and bromocriptine (dopamine agonist).
• Onset is typically within days to 2 weeks of neuroleptic initiation or an increase in dosage.
• Key differential: Serotonin syndrome (distinguished by hyperreflexia, myoclonus, and different causative agents).