Is plasma exchange (plasma exchange) recommended prior to thymectomy in patients with severe or unstable myasthenia gravis (myasthenia gravis)?

Plasma Exchange Prior to Thymectomy in Myasthenia Gravis

Plasma exchange is recommended prior to thymectomy in patients with severe or unstable myasthenia gravis to reduce perioperative complications and improve long-term outcomes. 1, 2

Preoperative Assessment and Patient Selection

Medical control of myasthenia gravis must be achieved before any surgical procedure. 3, 1, 2 The following assessment is essential:

• Measure vital capacity (VC) and negative inspiratory force (NIF) to assess respiratory function 1
• Apply the "20/30/40" rule to identify patients at high risk for respiratory failure: VC <20 mL/kg, maximum inspiratory pressure <30 cm H2O, or maximum expiratory pressure <40 cm H2O 1
• Evaluate for severe symptoms including dysphagia, notable weight loss, severe weakness, or inability to lift arms 1, 2
• Check acetylcholine receptor (AChR) antibody levels in all patients, even those without symptoms, to avoid respiratory failure during surgery 1, 2

Treatment Recommendations: Plasma Exchange vs IVIG

When to Use Plasma Exchange

Plasma exchange should be used in high-risk patients including those with:

• Severe generalized weakness (Osserman class IIA or IIB) 4
• Respiratory compromise or impending myasthenic crisis 5
• Thymoma-associated myasthenia gravis, which has increased frequency of myasthenic crisis and often responds poorly to immunosuppression 5

Plasma Exchange Protocol

The standard protocol involves 5 sessions of plasma exchange (200-250 mL plasma/kg body weight or 1-L exchanges) performed every other day, 10-30 days before surgery 3, 6, 4. The procedure should:

• Exchange twice the blood volume with fresh-frozen plasma or 5% albumin 3
• Be performed 3.2 ± 1.5 times on average before thymectomy 4
• Be completed with surgery ideally performed within 2 weeks 7

Evidence Supporting Plasma Exchange

A retrospective study of 51 patients demonstrated significant benefits of preoperative plasma exchange 4:

• Only 5.3% of patients treated with plasma exchange had crisis within 1 year post-thymectomy versus 28.1% without plasma exchange (p=0.049) 4
• No postoperative crisis within 30 days in the plasma exchange group versus 15.6% in the non-plasma exchange group 4
• 100% improvement rate and 79% pharmacologic remission at 5-7 years with plasma exchange versus 81.3% improvement and 50% remission without it (p<0.05) 4

Alternative: IVIG as First-Line Therapy

IVIG may be preferred over plasma exchange in most patients due to easier administration, wider availability, and fewer complications 3, 1. The protocol is:

• 0.4 g/kg/day for 5 consecutive days (total 2 g/kg) 3, 1, 7
• Improvement begins 1-9 days after starting (mean 3.33 days) 7
• Thymectomy should be performed within 2 weeks after IVIG treatment to minimize perioperative complications 7

Comparative Evidence: IVIG vs Plasma Exchange

A randomized trial of 24 patients showed IVIG superiority in several outcomes 6:

• Significantly shorter intubation period (p=0.01) 6
• Shorter duration of surgery (p=0.05) 6
• Reduced ICU length of stay and total hospitalization 6

However, plasma exchange remains effective and established for preoperative preparation, particularly in thymoma-associated cases 5, 4.

Selective vs Routine Approach

Selective use of plasma exchange for high-risk patients is recommended rather than routine use in all cases 8. A retrospective analysis of 164 patients demonstrated:

• Selective protocol reduced plasma exchange-related complications from 25.7% to 8.9% (p<0.05) 8
• No difference in postoperative mechanical ventilation duration, ICU stay, or hospital stay between routine and selective approaches 8

High-Risk Criteria for Plasma Exchange

Patients requiring preoperative plasma exchange include those with:

• Severe generalized weakness or bulbar symptoms 1, 4
• Respiratory compromise (VC <20 mL/kg or NIF <30 cm H2O) 1
• Thymoma-associated myasthenia gravis 5
• Previous myasthenic crisis or poor response to immunosuppression 5

Special Considerations

Check serum IgA levels before administering IVIG, as IgA deficiency may lead to severe anaphylaxis 1.

Continue anticholinesterase medications (pyridostigmine) perioperatively unless contraindicated 1.

Monitor closely for myasthenic crisis postoperatively, including respiratory failure, and consider early tracheostomy in high-risk patients (those unable to lift arms from bed at 1 week after intubation or with axonal subtype on electrophysiology) 1.

Clinical Algorithm

1. Assess all myasthenia gravis patients preoperatively with VC, NIF, and AChR antibodies 1
2. For high-risk patients (severe weakness, respiratory compromise, thymoma): Use plasma exchange (5 sessions over 10 days) OR IVIG (0.4 g/kg/day × 5 days) 6, 4, 8
3. For stable, mild disease: Consider IVIG alone or proceed to surgery with medical optimization 8
4. Perform thymectomy within 2 weeks of completing immunomodulatory therapy 7
5. Prepare for postoperative complications with ICU monitoring and mechanical ventilation availability 1, 4