What is the recommended treatment for a patient diagnosed with Acute Motor Sensory Axonal Neuropathy (AMSAN), a variant of Guillain-Barré Syndrome (GBS)?

Treatment of Acute Motor Sensory Axonal Neuropathy (AMSAN)

Treat AMSAN with intravenous immunoglobulin (IVIg) 0.4 g/kg/day for 5 consecutive days (total dose 2 g/kg) as first-line therapy, though evidence suggests this treatment may be less effective in axonal variants compared to demyelinating forms of Guillain-Barré syndrome. 1, 2

First-Line Treatment Protocol

IVIg is the preferred first-line treatment despite limited efficacy data specific to AMSAN, administered at 0.4 g/kg body weight daily for 5 consecutive days. 1, 2, 3 This preference is based on easier administration, wider availability, and higher completion rates compared to plasma exchange. 1, 3

Plasma exchange (5 sessions of 200-250 ml/kg) is an equally acceptable alternative if IVIg is contraindicated, unavailable, or cost is prohibitive. 2, 3 However, the American Academy of Neurology considers both treatments equivalent overall for GBS variants. 1, 2

Critical Evidence Gap for Axonal Variants

A major caveat exists: IVIg may not be beneficial specifically in axonal forms like AMSAN. A 2022 study comparing IVIg to natural course found that while IVIg reduced poor recovery at 6 months in AIDP (0.8% vs 6.6%, p=0.03), it did not alter outcomes in AMAN patients. 4 The axonal forms appear mediated by anti-ganglioside antibodies that inhibit sodium channels—a different pathophysiological mechanism than demyelinating forms—which may explain reduced treatment efficacy. 2

Despite this evidence suggesting limited benefit, current guidelines do not differentiate treatment recommendations between AMSAN and AIDP subtypes, and both IVIg and plasma exchange remain standard first-line options. 1

Timing and Initiation Criteria

• Initiate treatment immediately in patients unable to walk unaided with moderate to severe weakness, especially with rapid progression. 3
• Begin within 2 weeks of symptom onset for maximum effectiveness. 1, 3
• AMSAN patients often present later and more severely than AIDP patients, making early recognition crucial. 3

Critical Monitoring Requirements

Admit all AMSAN patients to a monitored unit with rapid ICU transfer capability, as approximately 25% of GBS patients develop respiratory failure. 1, 3

Respiratory Monitoring ("20/30/40 Rule")

Patient is at risk for respiratory failure if: 1, 2, 3

• Vital capacity <20 ml/kg
• Maximum inspiratory pressure <30 cmH₂O
• Maximum expiratory pressure <40 cmH₂O

Calculate the Erasmus GBS Respiratory Insufficiency Score (EGRIS) to predict probability of requiring mechanical ventilation within 1 week. 1, 2, 3

Additional Monitoring

• Continuous cardiac monitoring for arrhythmias and blood pressure instability due to autonomic dysfunction. 2
• Monitor bowel and bladder function for autonomic involvement. 2
• Assess swallowing and coughing difficulties to prevent aspiration. 5
• Serial neurologic examinations using Medical Research Council grading scale and GBS disability scale. 5

Medications to Strictly Avoid

Never use the following medications as they worsen neuromuscular function: 1, 2, 3

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

Never use corticosteroids alone—they are ineffective and may worsen outcomes. 1, 2, 3

Managing Treatment Response

Expected Initial Response

Approximately 40% of patients do not improve in the first 4 weeks following treatment, which does not necessarily indicate treatment failure, as progression might have been worse without therapy. 5, 1, 3

Treatment-Related Fluctuations (TRFs)

If clinical deterioration occurs within 2 months after initial improvement or stabilization, this represents a treatment-related fluctuation (occurs in 6-10% of patients). 5, 1, 2, 3 Repeat the full course of IVIg or plasma exchange in these cases, as this indicates the treatment effect has worn off while inflammation continues. 5, 1, 2, 3

Severe Cases Without Response

For severe axonal GBS cases on mechanical ventilation with no improvement after initial IVIg, a second cycle of IVIg using the same dose and regimen may be considered after 6 weeks, though this is based on limited case report evidence. 6 One small case series showed patients weaned off mechanical ventilation approximately 5 days after second infusion. 6

Do not routinely give a second course of IVIg to patients with poor prognosis outside of TRFs, as this increases serious adverse events without proven benefit. 1

Supportive Care Essentials

Pain Management

• Use gabapentin, pregabalin, or duloxetine for neuropathic pain. 2, 3
• Avoid opioids as first-line for pain management. 2, 3

Other Supportive Measures

• DVT prophylaxis for immobilized patients. 3
• Pressure ulcer prevention with frequent repositioning. 5
• Treatment of constipation/ileus, which is common. 5, 3
• Nutritional support if dysphagia present. 3

Prognosis for AMSAN

AMSAN typically has worse outcomes than demyelinating forms. 2 Overall GBS mortality is 3-10%, primarily from cardiovascular and respiratory complications. 1, 2, 3 About 80% of GBS patients overall regain walking ability at 6 months, but this figure may be lower for AMSAN given the axonal damage. 1, 2, 3

Calculate the modified Erasmus GBS Outcome Scale (mEGOS) on admission to predict prognosis. 2 Recovery can continue beyond 3 years after onset. 2

Up to two-thirds of deaths occur during the recovery phase, mostly from cardiovascular and respiratory dysfunction, so maintain vigilance even after ICU discharge, especially in patients with cardiovascular risk factors. 5