Guillain-Barré Syndrome (GBS)

Overview

GBS is an acute, autoimmune polyradiculoneuropathy — frequently severe and potentially fulminant. It occurs year-round at 10–20 cases per million annually (~5,000–6,000 cases/year in the US). Males are slightly more affected than females; in Western countries, adults more than children. (Harrison's, p. 12718)

Pathophysiology

GBS is triggered by molecular mimicry: a preceding infection induces antibodies that cross-react with peripheral nerve gangliosides and myelin antigens.

Common precipitants (1–4 weeks prior):

Campylobacter jejuni (most common, ~30%)
Cytomegalovirus (CMV)
Epstein-Barr virus (EBV)
Mycoplasma pneumoniae
COVID-19, Zika virus
Vaccines (rare)

Subtypes

Subtype	Mechanism	Key Feature
AIDP (most common in West)	Demyelinating	Slow conduction velocity
AMAN	Axonal, motor	Anti-GM1/GD1a antibodies
AMSAN	Axonal, motor + sensory	Worse prognosis
Miller Fisher Syndrome	Anti-GQ1b antibodies	Ophthalmoplegia, ataxia, areflexia
Bickerstaff's encephalitis	Anti-GQ1b, CNS involvement	Altered consciousness

Clinical Features

Progression: Ascending weakness + sensory symptoms → nadir by 4 weeks

Motor: Bilateral limb weakness (legs → arms), facial diplegia
Sensory: Paresthesias, pain (back/leg pain common early)
Autonomic: Tachycardia, BP fluctuation, urinary retention, ileus (life-threatening)
Respiratory: Diaphragm weakness → respiratory failure in ~25–30%
Reflexes: Areflexia/hyporeflexia is a hallmark

Plateau phase typically lasts 2–4 weeks, then gradual recovery.

Diagnosis

CSF (Lumbar Puncture)

Classic finding: Albuminocytologic dissociation
- Elevated protein (>45 mg/dL, often >100)
- Normal or near-normal cell count (<10 WBC/µL)
- Seen in ~80% at 2 weeks

Electrodiagnostics (NCS/EMG)

AIDP: Prolonged distal latencies, slowed conduction velocity, conduction block, prolonged F-waves
AMAN/AMSAN: Reduced CMAP amplitudes with relatively preserved conduction velocity

Antibody Testing

Anti-GQ1b → Miller Fisher Syndrome
Anti-GM1 → AMAN
Anti-GD1b → sensory GBS

MRI

Gadolinium enhancement and thickening of nerve roots (cauda equina) is a classic radiological finding:

MRI of cauda equina in GBS — axial T2 (left) shows thickened intradural ventral nerve roots (yellow arrows); T1 post-contrast (right) shows gadolinium enhancement indicating blood-nerve barrier breakdown, consistent with AIDP

Management

ICU Monitoring Criteria (admit all suspected GBS)

Serial FVC monitoring — intubate if FVC <20 mL/kg, MIP <30 cmH₂O, MEP <40 cmH₂O ("20-30-40 rule")
Continuous cardiac monitoring (autonomic instability)
DVT prophylaxis

Immunotherapy

Initiated as soon as possible — within ~2 weeks of first motor symptoms (Harrison's, p. 12730):

Therapy	Dose	Notes
IVIg (preferred first-line)	2 g/kg total over 5 days	Easy to administer; good safety profile
Plasmapheresis (PLEX)	5 exchanges over 2 weeks	Equally effective
Combination	Not recommended	No added benefit over either alone

Steroids (corticosteroids) are NOT effective in GBS and not recommended.

Supportive Care

Pain management (gabapentin, carbamazepine, opioids for severe cases)
Bowel/bladder care
Physical and occupational therapy
Nutritional support (NG/PEG if bulbar dysfunction)

Prognosis

~85% walk independently at 6 months
~5–10% mortality (respiratory failure, autonomic instability, sepsis)
~20% have significant residual disability at 1 year
Predictors of poor outcome: older age, rapid progression, axonal subtype (AMAN/AMSAN), preceding C. jejuni infection, low CMAP amplitudes

EGOS/mEGOS score can estimate probability of independent ambulation at 6 months.

Key Differentiators from Mimics

Feature	GBS	Transverse Myelitis	CIDP	MG
Reflexes	Absent	Absent/hyperreflexia	Reduced	Normal
Sensory level	No	Yes	Variable	No
CSF protein	High	Variable	High	Normal
Progression	<4 weeks	Hours–days	>8 weeks	Fatigable
Autonomic	Common	Bladder/bowel	Rare	Rare

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