What is the treatment for the AMSAN (Acute Motor-Sensory Axonal Neuropathy) variant of Guillain-Barré Syndrome?

Treatment for AMSAN Variant of Guillain-Barré Syndrome

Treat AMSAN with either intravenous immunoglobulin (IVIg) 0.4 g/kg/day for 5 days or plasma exchange (5 sessions of 200-250 ml/kg), though evidence suggests these treatments may be less effective in axonal variants compared to demyelinating forms. 1

First-Line Treatment Options

The standard immunomodulatory treatments for all GBS variants, including AMSAN, are:

• IVIg at 0.4 g/kg body weight daily for 5 consecutive days (total dose 2 g/kg) 1, 2
• Plasma exchange: 5 sessions at 200-250 ml/kg 1

Both treatments are considered equally effective overall, though IVIg is generally preferred due to easier administration, wider availability, and higher completion rates 2. However, this equivalence may not hold true specifically for AMSAN.

Critical Evidence Regarding Axonal Variants

A major caveat exists for AMSAN treatment: Recent research demonstrates that IVIg therapy does not significantly alter outcomes in acute motor axonal neuropathy (AMAN), the pure motor axonal variant 3. While AMSAN (acute motor-sensory axonal neuropathy) was not specifically studied in this trial, the shared axonal pathophysiology suggests similar treatment resistance may occur 3, 4.

The axonal forms (AMAN and AMSAN) may be mediated by anti-ganglioside antibodies that inhibit sodium channels, representing a different pathophysiological mechanism than demyelinating forms 4. This mechanistic difference may explain why standard immunomodulatory treatments show reduced efficacy in axonal variants 3.

Treatment Algorithm for AMSAN

Despite limited efficacy data, initiate treatment promptly with one of the following:

1. Start IVIg 0.4 g/kg/day for 5 days as first-line therapy due to ease of administration 2

   • Monitor serum IgG levels post-treatment, as patients with minor IgG increases recover significantly slower 5
   • Consider second IVIg course if poor response and low IgG increase 5

2. Alternative: Plasma exchange (5 sessions) if IVIg contraindicated or unavailable 1

3. Do NOT use corticosteroids alone - they provide no benefit and may worsen outcomes 6, 2

Essential Monitoring and Supportive Care

Respiratory monitoring is critical in AMSAN:

• Admit to unit with rapid ICU transfer capability 7, 2
• Apply the "20/30/40 rule": patient at risk if vital capacity <20 ml/kg, maximum inspiratory pressure <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O 2
• Calculate Erasmus GBS Respiratory Insufficiency Score (EGRIS) to predict ventilation need 2, 5
• Approximately 25% of GBS patients require mechanical ventilation 5

Autonomic dysfunction monitoring:

• Continuous cardiac monitoring for arrhythmias and blood pressure instability 7
• Monitor bowel/bladder function 7

Pain management:

• Use gabapentin, pregabalin, or duloxetine for neuropathic pain 6
• Avoid opioids as first-line 6

Medications to Avoid

Strictly avoid drugs that worsen neuromuscular function: 6, 2

• β-blockers
• IV magnesium
• Fluoroquinolones
• Aminoglycosides
• Macrolides

Prognosis Considerations

AMSAN typically has worse outcomes than demyelinating forms:

• Overall GBS mortality is 3-10%, primarily from cardiovascular and respiratory complications 7, 2
• About 80% of GBS patients regain walking ability at 6 months, but this figure may be lower for AMSAN given the axonal damage 7, 2
• Recovery can continue beyond 3 years after onset 1
• Calculate modified Erasmus GBS Outcome Scale (mEGOS) on admission to predict prognosis 1

Treatment-Related Fluctuations

• Occur in 6-10% of patients within 2 months of initial improvement 2
• Repeat full course of IVIg or plasma exchange if fluctuations occur 2
• The 5-day IVIg regimen is preferred over shorter regimens as treatment-related fluctuations are more frequent with abbreviated courses 7