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AIDP

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"acute inflammatory demyelinating polyneuropathy" OR "Guillain-Barre syndrome"

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Acute Inflammatory Demyelinating Polyneuropathy (AIDP)

AIDP is the classic and most common subtype of Guillain-Barré Syndrome (GBS), accounting for the majority of GBS cases in Europe and North America. It is an acquired, immune-mediated polyneuropathy characterized by acute demyelination of peripheral nerve roots and nerves.

Definition & Classification

AIDP is defined by the diagnostic criteria for GBS with confirmed demyelinating electrophysiology. GBS itself is a heterogeneous syndrome with several subtypes:
SubtypePathologyNotes
AIDPDemyelinationMost common in Europe/North America
AMANAxonal (motor)Summer epidemics in China; children/young adults
AMSANAxonal (motor + sensory)Severe, poor recovery
Miller-Fisher SyndromeNodes of RanvierOphthalmoplegia, ataxia, areflexia
Pharyngeal-cervical-brachialVariantBulbar-predominant
Acute pandysautonomiaAutonomicRare
  • Bradley and Daroff's Neurology in Clinical Practice, p. 2663

Epidemiology

  • Mean annual incidence: 1.8 per 100,000
  • More common in males (M:F = 1.5:1)
  • All ages affected; incidence rises with age (0.8/100,000 in <18 yr to 3.2/100,000 in >60 yr)
  • GBS is now the leading cause of acute flaccid paralysis in Western countries (since polio eradication)
  • Mortality has fallen from ~33% (pre-ventilation era) to 1-5% currently
  • Bradley and Daroff's Neurology, p. 2663

Pathogenesis

Trigger: ~2/3 of cases are preceded by an infection 1-2 weeks before onset. Key organisms include:
  • Campylobacter jejuni (most common bacterial trigger)
  • Cytomegalovirus (CMV)
  • Epstein-Barr virus (EBV)
  • HIV
  • Zika virus
  • SARS-CoV-2
Mechanism - Molecular Mimicry:
  • Infection triggers microbe-specific T cells and antibodies
  • These cross-react with peripheral nerve antigens (molecular mimicry)
  • Both T cell-mediated and antibody-mediated immunity are involved; T cells are believed to play the dominant role
  • Injury is most extensive in nerve roots and proximal nerve segments
  • Endoneurial perivascular mononuclear cell infiltration (rich in macrophages) with multifocal demyelination
  • Peripheral nerves affected from roots to distal intramuscular segments
  • Robbins & Kumar Basic Pathology, p. 809
  • Bradley and Daroff's Neurology, p. 2666

Clinical Features

Onset: Ascending, relatively symmetric weakness beginning in the legs, spreading proximally over days to a few weeks.

Diagnostic Criteria (Asbury & Cornblath, 1990)

Required:
  • Progressive weakness of both legs and arms
  • Areflexia or hyporeflexia
Supportive (Clinical):
  • Progression over days to 4 weeks (max)
  • Relative symmetry
  • Mild sensory symptoms
  • Bifacial palsies
  • Autonomic dysfunction
  • Absence of fever at onset
  • Recovery beginning 2-4 weeks after plateau
Supportive (Lab):
  • Elevated CSF protein with <10 cells/μL (albuminocytological dissociation)
  • Nerve conduction slowing or block on EDX

Key Clinical Points

  • Weakness ranges from mild (ambulatory) to near-total quadriplegia
  • Areflexia is invariable, though may be absent early
  • Cranial nerve involvement in 45-75%; bilateral facial paresis in >50%
  • Respiratory failure in 9-30% - requires mechanical ventilation
  • Sensory symptoms are relatively mild; vibration sense most affected distally
  • Pain occurs in ~70% during acute phase (back, radicular, dysesthetic); persists 1 year in ~1/3
  • Autonomic dysfunction in 65% of hospitalized patients - arrhythmias, BP fluctuations, ileus, urinary retention
  • Bradley and Daroff's Neurology, p. 2663-2664

Investigations

InvestigationFinding
CSFElevated protein (often >1 g/L), <10 WBC/μL (albuminocytological dissociation)
NCS (nerve conduction studies)Prolonged distal latencies, slowed conduction velocities, conduction block, prolonged or absent F-waves
EMGMay show denervation in severe or prolonged cases
Anti-ganglioside antibodiesAnti-GQ1b in Miller-Fisher; anti-GM1 in AMAN
MRI spineNerve root enhancement on contrast MRI (supportive)
The 20-30-40 Rule for respiratory monitoring:
  • FVC < 20 mL/kg, AND/OR
  • Maximal inspiratory pressure < 30 cmH₂O, AND/OR
  • Maximal expiratory pressure < 40 cmH₂O
Elective intubation when FVC falls below 12-15 mL/kg (or 18 mL/kg with oropharyngeal weakness), or PaO₂ < 70 mmHg on room air.
  • Bradley and Daroff's Neurology, p. 2669

Differential Diagnosis

  • Critical illness polyneuropathy
  • Vasculitic neuropathy
  • Heavy metal poisoning (thallium, arsenic)
  • Diffuse polyradiculopathy (Lyme, CMV, sarcoidosis, neoplastic)
  • Acute poliomyelitis (wild-type, West Nile, enteroviruses)
  • Transverse myelitis / spinal cord compression
  • Myasthenic crisis
  • Botulism
  • Tick paralysis
Key distinguishers: Normal CK (vs. myopathy), normal CMAPs with decremental response (vs. MG crisis), CSF pleocytosis >50 cells/μL argues against uncomplicated GBS.

Treatment

1. Supportive Care (Cornerstone)

  • Respiratory monitoring - serial FVC, pulse oximetry, ICU admission for high-risk patients
  • Elective intubation when indicated; tracheostomy if ventilation >2 weeks
  • Continuous ECG + BP monitoring for autonomic instability
  • Caution with antihypertensives - risk of precipitous hypotension; avoid tracheal suctioning-induced vagal responses
  • DVT prophylaxis - LMWH + pneumatic compression
  • Nutritional support (enteral feeding early if dysphagia)
  • Pain control - NSAIDs, then opioids if needed
  • Pressure ulcer prevention, physiotherapy, psychological support

2. Specific Immunotherapy (Equally Effective Options)

Plasma Exchange (Plasmapheresis):
  • Removes offending antibodies
  • 6 large RCTs (>600 patients) confirmed efficacy - shortens recovery time
  • Recommended for patients with moderate-to-severe weakness (can walk only with support or worse)
  • Best when started within 2 weeks of onset; effective up to 30 days
  • Schedule: 4-5 exchanges (40-50 mL/kg each) on alternate days, with saline/albumin replacement
  • Even mild cases benefit from 2 exchanges; 4 exchanges optimal for moderate/severe
Intravenous Immunoglobulin (IVIg):
  • Equally effective as plasma exchange
  • Dose: 0.4 g/kg/day for 5 days (total 2 g/kg)
  • Mechanism: suppresses immune responses (exact mechanism unclear)
  • Easier to administer; preferred in many centers
Corticosteroids: NOT beneficial in GBS (no evidence of effect; may worsen outcome)
Combination therapy (PE + IVIg): Not superior to either alone
  • Bradley and Daroff's Neurology, p. 2669-2670
  • Robbins & Kumar Basic Pathology, p. 809

Prognosis

  • Most patients reach nadir within 2-4 weeks
  • Recovery begins 2-4 weeks after plateau
  • With treatment, majority achieve complete or near-complete recovery
  • ~20% have residual weakness at 1 year
  • ~5% have a relapsing course (reclassified as CIDP if >8 weeks)
  • Mortality: 1-5% (due to respiratory failure, autonomic dysfunction, sepsis, PE)
  • Poor prognostic factors: older age, preceding C. jejuni infection, rapid onset, need for ventilation, axonal involvement on NCS
  • Neuroanatomy through Clinical Cases, 3rd ed., p. 352

AIDP vs CIDP (Key Distinction)

FeatureAIDP (GBS)CIDP
CourseAcute, peaks ≤4 weeksProgressive ≥2 months, or relapsing
TriggersPost-infectiousOften no clear trigger
TreatmentPE or IVIg (short course)Long-term steroids, IVIg, PE
PrognosisUsually good recoveryChronic/relapsing
Sources:
  • Bradley and Daroff's Neurology in Clinical Practice - Primary reference for GBS/AIDP
  • Robbins & Kumar Basic Pathology - Pathogenesis
  • Neuroanatomy through Clinical Cases, 3rd ed. - Clinical summary
  • Recent systematic review (2026): Exercise programs in GBS/CIDP - PMID 41038424 confirms exercise therapy aids functional recovery in rehabilitation phase
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