NeurologyTier 1Disease (DEADMAN)

Guillain-Barré syndrome

Description

Acute immune-mediated polyradiculoneuropathy - ascending, symmetric, areflexic weakness
Commonest cause of acute flaccid paralysis worldwide since polio control
Monophasic: progression <4 weeks (90% at nadir by 2 weeks), then plateau then recovery
- Progression >8 weeks = CIDP; 4-8 weeks = subacute IDP

Variants

Variant	Features
AIDP	Demyelinating; ~90% in Western countries; sensorimotor
AMAN	Pure motor, axonal; reflexes may be preserved or brisk; post-Campylobacter; Asia/South America
AMSAN	Axonal motor + sensory; more severe, slower recovery
Miller Fisher	Ataxia + ophthalmoplegia + areflexia; anti-GQ1b; ~5%; descending pattern, good prognosis
Pharyngeal-cervical-brachial	Bulbar + neck + arm weakness, legs spared; mimics botulism/myasthenia
Bickerstaff brainstem encephalitis	MFS features + dec conscious state + hyperreflexia; anti-GQ1b

Facial weakness (often bilateral) in ~50%; bulbar in ~40%
Autonomic involvement in ~2/3 - the reason these patients die

Epidemiology

1-2 per 100,000/yr; ~1 case per week in a large tertiary centre
M>F ~1.5:1
Incidence rises with age; small second peak in young adults
AIDP predominates in Australia/Europe/North America; AMAN in China, Japan, Mexico

Aetiopathogenesis

Antecedent event - ~2/3, within 6 weeks

Campylobacter jejuni ~30% - the strongest association; predicts axonal (AMAN) form and worse outcome
CMV (young, severe sensory, facial), EBV, Mycoplasma pneumoniae, hepatitis E, HIV seroconversion
Zika, influenza, SARS-CoV-2
Surgery, trauma, pregnancy/puerperium
Vaccines - risk is real but tiny (~1 extra case per million); far smaller than the risk from the infection itself
Immune checkpoint inhibitors

Mechanism - molecular mimicry

Microbial lipo-oligosaccharide shares epitopes with peripheral nerve gangliosides
-> cross-reactive IgG -> complement activation at the axolemma/Schwann cell -> conduction block, then degeneration
Anti-GM1 and anti-GD1a -> AMAN (nodes of Ranvier, motor axon)
Anti-GQ1b -> Miller Fisher / Bickerstaff - GQ1b is enriched in CN III, IV, VI
Anti-GT1a -> pharyngeal-cervical-brachial
Antibodies are useful confirmatory tests but are NOT required and are absent in most AIDP

Diagnosis

Clinical diagnosis. Do not wait for CSF or NCS to treat.

Core clinical features

Numbness, paraesthesia, weakness and limb/back pain (pain in ~2/3, often the first symptom and easily missed)
Progressive, relatively symmetric, bilateral limb weakness
Hyporeflexia or areflexia in weak limbs
Ascending (legs -> arms) in most; sensory signs mild relative to weakness

Red flags against GBS - reconsider the diagnosis

No sensory involvement at all -> polio/enterovirus, myasthenia gravis, hypokalaemia, acute myopathy, botulism
Abrupt paralysis with a sensory level or urinary retention -> spinal cord compression / transverse myelitis - image the cord
Marked persistent asymmetry
Fever at onset; CSF pleocytosis >50 cells (-> HIV, Lyme, CMV polyradiculitis, leptomeningeal malignancy)
Slow progression over months

CSF

Albuminocytologic dissociation - raised protein with a normal cell count
- Normal in up to 50% in the first week - a normal CSF early does NOT exclude GBS
- Sensitivity rises to ~80% by week 2
Cells 10-50 = possible; >50 = look for another cause

Nerve conduction studies

Most useful after ~1 week; may be normal early
Demyelinating (AIDP): prolonged distal motor latency, conduction block, temporal dispersion, slowed velocity, absent/prolonged F waves (earliest change), abnormal/absent H reflex
Axonal (AMAN): reduced CMAP amplitude, normal velocity, no conduction block
Sural sparing pattern (abnormal median/ulnar sensory with normal sural) is characteristic

Other

Spirometry / FVC at the bedside is the single most important investigation - repeat 4-6 hourly while progressing
MRI spine with gadolinium - enhancement of the cauda equina / anterior nerve roots; also excludes cord pathology
Anti-ganglioside antibodies (GQ1b if ophthalmoplegia), stool/serology for Campylobacter, HIV, hepatitis E
Exclude porphyria, lead, vasculitic neuropathy, tick paralysis, botulism, diphtheria

Management

A. Respiratory and autonomic surveillance - the priority

The 20/30/40 rule - consider ICU/intubation if:
- FVC <20 mL/kg, OR
- Max inspiratory pressure less negative than -30 cmH2O, OR
- Max expiratory pressure <40 cmH2O
Also intubate for: PaCO2 >48 mmHg, PaO2 <56 mmHg on room air, VC <15 mL/kg
- Do not wait for hypoxia or hypercapnia - by then it is a crash intubation
Bedside markers: single-breath count, inability to lift the head off the pillow, staccato speech
~20-30% require mechanical ventilation
EGRIS score at admission predicts ventilation need (days from onset, facial/bulbar weakness, MRC sum score)
Autonomic monitoring - continuous ECG, lying/standing BP
- Labile hypertension/hypotension, sinus tachycardia, bradyarrhythmia and asystole (especially on suctioning - atropine at the bedside), ileus, urinary retention
- Be very cautious with antihypertensives and sedatives - exaggerated responses

B. Immunotherapy

Treat if unable to walk unaided (Hughes >=3), or rapidly progressive, or bulbar/respiratory involvement
IVIg 0.4 g/kg/day for 5 days (2 g/kg total) - first-line in Australia; PBS/NBA criteria apply
- Start within 2 weeks of weakness onset
- Check IgA (anaphylaxis in IgA deficiency), renal function; risks: thrombosis, aseptic meningitis, haemolysis
Plasma exchange - 5 exchanges over 1-2 weeks; effective within 4 weeks of onset
- Equivalent efficacy to IVIg; choice driven by access, vascular access, haemodynamic stability
*PLEX then IVIg gives no added benefit - do not sequence them*
*A second IVIg course in poor responders does not help and increases thrombotic risk (SID-GBS)*
Corticosteroids are ineffective and are NOT indicated - this is the classic exam point; steroids alone may even delay recovery
Mild disease (still ambulant) and Miller Fisher usually managed supportively

C. Supportive care - where outcome is actually determined

VTE prophylaxis in every non-ambulant patient
Neuropathic pain - gabapentin or pregabalin first; opioids worsen ileus and autonomic instability
Swallow assessment before oral intake; early NG feeding
Pressure area care, splinting, contracture prevention, early physiotherapy
Bladder and bowel care
Psychological support - locked-in, painful, terrifying; delirium and vivid hallucinations are common in ICU
Rehabilitation from day 1; fatigue management long-term

Associations

*Campylobacter jejuni (axonal variants), CMV, EBV, Mycoplasma*, hepatitis E, HIV, Zika, influenza, SARS-CoV-2
Hodgkin lymphoma; SLE; sarcoidosis
Immune checkpoint inhibitors and, rarely, TNF inhibitors
Recent surgery, trauma, pregnancy and puerperium
CIDP - the chronic counterpart; ~5% of "GBS" declares itself as acute-onset CIDP

Natural history & complications

Monophasic: progression <4 weeks -> plateau (days-weeks) -> recovery over months
~80% walk independently at 6 months; conversely ~20% still cannot walk at 6 months
Mortality 3-5% even in good units - respiratory failure, autonomic arrhythmia, PE, sepsis
Residual deficit in ~1/3 - fatigue, distal weakness, sensory symptoms, pain
Treatment-related fluctuation in ~10% - deterioration after initial improvement within 8 weeks; re-treat
- Distinguish from acute-onset CIDP: >2 fluctuations or deterioration after 8 weeks = CIDP, and that patient needs maintenance therapy

Poor prognostic factors (mEGOS)

Older age, rapid onset (<7 days to admission), severe weakness (low MRC sum score)
*Preceding diarrhoea / Campylobacter***
Axonal (AMAN/AMSAN) pattern; low distal CMAP amplitude
Need for ventilation

Complications

Respiratory failure and ventilator-associated pneumonia; aspiration
Autonomic dysfunction - arrhythmia, asystole, extreme hypertension or hypotension
VTE
Pain (acute and chronic), pressure injury, contracture
SIADH; ICU-acquired weakness; anxiety/depression, PTSD

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