Guillain-Barré syndrome

Epidemiology

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Etiology

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• Acute inflammatory demyelinating polyneuropathy of the peripheral nervous system.
• Autoimmune process triggered by a preceding infection (1-3 weeks prior).
  • Most common association: Campylobacter jejuni gastroenteritis.
  • Other associations: CMV, EBV, influenza, Zika virus, recent vaccination.
• Mechanism: Molecular mimicry, where antibodies against the infectious agent cross-react with gangliosides on the myelin sheath of peripheral nerves. c
• Results in demyelination and axonal damage, leading to impaired nerve conduction.

Pathophysiology

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Clinical features

• Motor:
  • Ascending, symmetric flaccid paralysis/weakness (lower extremities → trunk/upper extremities → bulbar/respiratory muscles).
  • Areflexia or hyporeflexia (absent or diminished DTRs; hallmark finding).
• Sensory:
  • Mild distal paresthesias/numbness (“stocking-glove” distribution); neuropathic pain (back, buttocks, thighs).
• Autonomic Instability (up to 70% of cases):
  • Labile BP, orthostatic hypotension, resting tachycardia, severe bradycardia/arrhythmias, urinary retention, paralytic ileus.
• Cranial Nerves:
  • Bilateral facial nerve palsy (CN VII) is classic; dysphagia, dysarthria.
• Variant:
  • Miller Fisher Syndrome: Triad of ophthalmoplegia, ataxia, and areflexia with minimal extremity weakness. Strongly linked to anti-GQ1b antibodies.

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Diagnostics

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• Initial Bedside Respiratory Assessment (Priority):
  • Serial Spirometry: Measure Forced Vital Capacity (FVC) and Negative Inspiratory Force (NIF) / Maximum Inspiratory Pressure (MIP).
  • High-risk thresholds: FVC $\le$ 20 mL/kg or NIF $\le$ –30 cmH₂O (indicates impending respiratory failure).
• Initial Diagnostic Test / Key Labs:
  • Lumbar Puncture (LP) / CSF Analysis: Albuminocytologic dissociation (↑ CSF protein with normal CSF WBC count $<5/\mu \text{L}$). c
    • Autoimmune response, not infection
  • Note: Protein may be normal in the first 7 days; repeat LP if suspicion remains high.
• Confirmatory / Most Specific Test:
  • Electromyography & Nerve Conduction Studies (EMG/NCS): Demyelinating pattern (↓ nerve conduction velocity, prolonged distal latencies, conduction blocks).
• Serology (Specific Subtypes):
  • Anti-GQ1b IgG autoantibodies (Miller Fisher syndrome).
  • Anti-GM1, anti-GD1a (axonal variants).

Treatment

1. Airway & Respiratory Monitoring (First Priority):
   • Admit to ICU for telemetry and serial FVC/NIF monitoring (every 2–4 hours).
   • Elective Endotracheal Intubation: Indicated if FVC $<20\text{ mL/kg}$, NIF $<-30{\text{ cmH}}_2\text{O}$, rapid downward trajectory, or severe autonomic/bulbar dysfunction (do not wait for ABG deterioration).
2. First-line Disease-Modifying Therapy (Initiate promptly):
   • Intravenous Immune Globulin (IVIG): $0.4\text{ g/kg/day}$ for 5 days. c
   • Plasma Exchange (PLEX / Plasmapheresis): Equally efficacious to IVIG; preferred if IVIG contraindicated (e.g., IgA deficiency).
   • Note: Combination of IVIG + PLEX has no added benefit.
3. Contraindicated Therapy:
   • Systemic Corticosteroids: NOT effective; potentially delay recovery (frequent Step 2 board trap). c
     • Can’t remove existing antibodies
4. Supportive Care:
   • DVT/PE Prophylaxis: LMWH + sequential compression devices (high risk due to flaccid immobility).
   • Hemodynamic Support: Judicious use of short-acting anti-HTN or vasopressors for autonomic instability.
   • Neuropathic Pain: Gabapentin, pregabalin, or NSAIDs.
   • Rehabilitation: Early physical and occupational therapy.