What are the variants of Guillain‑Barré syndrome?

Variants of Guillain-Barré Syndrome

Guillain-Barré syndrome encompasses several distinct clinical variants beyond the classic sensorimotor form, including pure motor variant, Miller Fisher syndrome, regional variants (bilateral facial palsy with paresthesias, pharyngeal-cervical-brachial weakness, paraparetic variant), and the electrophysiological subtypes AIDP, AMAN, and AMSAN. 1

Core Clinical Variants

Classic Sensorimotor GBS

• Accounts for approximately 70% of cases in Europe and the Americas, but only 30-40% in Asia 2
• Presents with rapidly progressive bilateral ascending weakness starting in legs, progressing to arms and cranial muscles, accompanied by sensory symptoms 1
• Diminished or absent reflexes are characteristic, typically beginning in lower limbs 2

Pure Motor Variant

• Represents 5-70% of cases depending on geographic region 2
• Characterized by motor weakness without sensory signs 1
• A critical pitfall: patients with pure motor variant and AMAN subtype can have normal or even exaggerated reflexes throughout the disease course, which can delay diagnosis 1, 3

Miller Fisher Syndrome (MFS)

• Comprises 5-25% of GBS cases 2
• The classic triad consists of ophthalmoplegia, areflexia, and ataxia 1
• Anti-GQ1b antibodies are present in up to 90% of cases, providing the most specific serologic marker 2
• Carries a 15-30% risk of respiratory failure despite the distinct clinical presentation 2

Regional Variants

Bilateral Facial Palsy with Paresthesias

• Weakness limited to cranial nerves 1
• Can be the presenting feature before limb weakness develops 2
• Bilateral simultaneous facial weakness is extremely rare in Bell's palsy and should immediately raise suspicion for GBS 2

Pharyngeal-Cervical-Brachial Weakness

• Weakness confined to upper limbs and bulbar muscles 1
• Requires immediate anti-ganglioside antibody testing (particularly anti-GQ1b) when bulbar symptoms are present 2

Paraparetic Variant

• Weakness limited to lower limbs 1

Electrophysiological Subtypes

Acute Inflammatory Demyelinating Polyneuropathy (AIDP)

• The most common subtype in Western populations 4
• Characterized by demyelinating features on nerve conduction studies 1
• Electrodiagnostic criteria vary widely: applying six different published criteria to the same GBS population yielded AIDP classification rates ranging from 21% to 72% 5

Acute Motor Axonal Neuropathy (AMAN)

• More prevalent in Asian populations 2
• Characterized by markedly reduced or absent compound muscle action potentials reflecting primary motor axonal degeneration 2
• Can present with normal or exaggerated reflexes, a key diagnostic pitfall 1

Acute Motor and Sensory Axonal Neuropathy (AMSAN)

• Features both motor and sensory axonal damage 1, 4
• Associated with more severe outcomes: at 12 months, median GBS disability scale was 1 for axonal forms versus 0 for demyelinating forms 6
• Axonal degeneration on two successive early nerve conduction studies may predict poor outcome 6

Debated Variants

The following are often included in the GBS spectrum but do not fulfill diagnostic criteria for GBS:

• Pure sensory variant: shares clinical features with classic GBS except lacks motor symptoms 1
• Pure sensory ataxia: overlaps clinically with Miller Fisher syndrome 1
• Bickerstaff brainstem encephalitis (BBE): presents with MFS-like symptoms but subsequently develops brainstem dysfunction including impaired consciousness and pyramidal tract signs 1

These variants can exhibit anti-GQ1b or other ganglioside antibodies similar to MFS, but their classification as GBS variants remains subject to debate 1

Critical Classification Considerations

Overlap and Impurity

• GBS variants are rarely 'pure' and often overlap with the classic syndrome or show features typical of other variant forms 1
• Approximately one-third of patients cannot be classified into AIDP, AMAN, or AMSAN at initial presentation and are labeled "equivocal" or "inexcitable" 1, 4

Repeat Testing

• Repeating electrodiagnostic studies 3-8 weeks after disease onset may aid classification of initially unclassifiable cases, though this practice remains controversial 1, 4

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 4
• The traditional demyelinating versus axonal dichotomy is increasingly challenged in clinical practice 4

Pediatric Considerations

Young children (<6 years) can present with atypical features that delay diagnosis:

• Poorly localized pain 1
• Refusal to bear weight 1, 2
• Irritability 1, 2
• Meningism 1
• Unsteady gait 1