Acute Inflammatory Demyelinating Polyradiculoneuropathy (AIDP)

Definition

• Bradley and Daroff's Neurology in Clinical Practice, p. 2663
• Goldman-Cecil Medicine, p. 4080

Etiopathogenesis

• Annual incidence: 1-2 per 100,000; males > females (1.4-1.5:1)
• A preceding infection (60% of cases) triggers an autoimmune response via molecular mimicry - the immune system mistakenly attacks peripheral nerve antigens that resemble microbial antigens
• Common triggers: upper respiratory tract infection, gastroenteritis (Campylobacter jejuni, Epstein-Barr virus, CMV, Zika virus, Hepatitis E)
• The immune attack targets the Schwann cell myelin sheath of spinal roots and peripheral nerves, producing multifocal inflammatory demyelination
• T-lymphocytes and macrophages infiltrate nerve roots; macrophages strip myelin from otherwise intact axons

Clinical Features

• Progressive, relatively symmetrical ascending weakness beginning in the legs and spreading to arms, respiratory muscles, and cranial nerves
• Hyporeflexia or areflexia (invariable feature)
• Respiratory failure requiring ventilation in 9%-30% of patients
• Cranial nerve involvement in 45%-75%: bilateral facial paresis (50%), extraocular muscle involvement, bulbar weakness

• Paresthesias and sensory loss (usually mild and distal)
• Moderate to severe pain in extremities or back in ~70% during acute phase

• Orthostatic hypotension, sinus tachycardia, cardiac arrhythmias (heart block, asystole from vagal spells)
• Urinary retention, GI atony, anhidrosis or episodic diaphoresis
• ECG changes: T-wave abnormalities, QT prolongation, ST depression

Diagnostic Criteria (Asbury & Cornblath criteria)

1. Progressive weakness of both legs and arms
2. Areflexia or hyporeflexia

• Progression over days to 4 weeks
• Relative symmetry
• Mild sensory symptoms
• Bifacial palsies, autonomic dysfunction
• Absence of fever at onset
• Recovery begins 2-4 weeks after progression ceases

• CSF: Elevated protein with <10 cells/uL - classic albuminocytological dissociation (cytoalbuminologic dissociation); normal in up to 10% in first week
• Nerve conduction studies (NCS): Reduced conduction velocities, prolonged distal latencies, conduction blocks, absent F-waves (evidence of demyelination)

Subtypes of GBS (for context)

Treatment

1. Supportive care - ICU monitoring, mechanical ventilation if FVC <15-20 mL/kg
2. Intravenous immunoglobulin (IVIg) - 0.4 g/kg/day for 5 days; equally effective as plasmapheresis
3. Plasmapheresis (plasma exchange) - 4-6 exchanges over 2 weeks; removes circulating antibodies
4. Note: Corticosteroids are NOT effective in GBS and are not recommended
5. DVT prophylaxis, pain management, physiotherapy, nasogastric feeding if bulbar involvement

Prognosis

• 50% reach maximum disability within 2 weeks, >90% within 4 weeks
• Mortality: ~3% (1-5%) with modern ICU care (previously 33% before positive-pressure ventilation)
• Most patients recover completely or with minor residual deficits
• 20% have persistent disability
• Poor prognosis predictors: older age, preceding diarrheal illness (C. jejuni), severe weakness, axonal variants, low CMAP amplitudes
• Goldman-Cecil Medicine, p. 4083; Bradley and Daroff's Neurology, p. 2663-2670