Primary Types of Guillain-Barré Syndrome
GBS is classified into three main electrophysiological subtypes—AIDP (acute inflammatory demyelinating polyneuropathy), AMAN (acute motor axonal neuropathy), and AMSAN (acute motor and sensory axonal neuropathy)—plus several distinct clinical variants including Miller Fisher syndrome. 1, 2
Main Electrophysiological Subtypes
AIDP (Acute Inflammatory Demyelinating Polyneuropathy)
- This is the classic demyelinating form that accounts for approximately 90% of GBS cases in Western countries 3
- Characterized by demyelination of peripheral nerves with both motor and sensory involvement 4
- Cranial nerve involvement occurs in 30-50% of AIDP cases 5
- Electrodiagnostic studies show demyelinating features, though international consensus on specific criteria remains elusive 1
AMAN (Acute Motor Axonal Neuropathy)
- A pure motor variant characterized by axonal damage without sensory signs 2, 4
- More prevalent in Asia, South and Central America 3
- Strongly associated with preceding Campylobacter jejuni infection 4, 3
- Mediated by anti-ganglioside antibodies (particularly anti-GD1a) that target axons 5
- Notably, cranial nerve involvement is NOT observed in AMAN, distinguishing it from AIDP 5
AMSAN (Acute Motor and Sensory Axonal Neuropathy)
- Features both motor and sensory axonal damage 1, 4
- Also more common in Asia, South and Central America 3
- Frequently preceded by Campylobacter jejuni infection 4
- Represents the most severe axonal form with both motor and sensory nerve involvement 4
Clinical Variants
Miller Fisher Syndrome (MFS)
- Characterized by the classic triad: ophthalmoplegia, areflexia, and ataxia 2, 5
- May also present with cranial nerve dysfunction 5
- Associated with anti-GQ1b ganglioside antibodies 5
- Represents a distinct clinical phenotype rather than an electrophysiological subtype 2
Regional Variants
- Bilateral facial palsy with paresthesias 2
- Pharyngeal-cervical-brachial weakness 2
- Paraparetic variant (affecting primarily lower extremities) 2
Important Clinical Considerations
Diagnostic Classification Challenges
- Approximately one-third of patients cannot be classified into AIDP, AMAN, or AMSAN at initial presentation and are labeled "equivocal" or "inexcitable" 1
- Repeating electrodiagnostic studies 3-8 weeks after onset may help classify initially unclassifiable cases, though this practice remains controversial 1
- The traditional demyelinating versus axonal dichotomy is increasingly challenged and is not endorsed by recent European Academy of Neurology/Peripheral Nerve Society guidelines 6
Treatment Implications
- Treatment approach does not differ based on electrophysiological subtype—both IVIg and plasma exchange are first-line regardless of whether the patient has AIDP, AMAN, or AMSAN 7, 6
- This makes the clinical distinction less critical for acute management decisions 6
Common Pitfall
- Do not assume normal reflexes rule out GBS, as the pure motor variant (AMAN) can occasionally have normal or even exaggerated reflexes 8
- The wide variability in electrodiagnostic criteria (ranging from 21% to 72% classified as AIDP depending on criteria used) means classification should not delay treatment 9