Treatment of Myasthenic Crisis
Myasthenic crisis requires immediate hospitalization with ICU-level monitoring, administration of IVIG (2 g/kg IV over 5 days) or plasmapheresis for 5 days, and frequent pulmonary function assessment to reduce mortality and improve outcomes. 1
Diagnosis and Initial Assessment
- Myasthenic crisis is defined as respiratory failure requiring mechanical ventilation or delayed postoperative extubation for more than 24 hours resulting from myasthenic weakness 2
- Perform immediate neurologic consultation and assessment of respiratory function with pulmonary function testing (NIF/VC) 1
- Check for anti-AChR antibodies and anti-striated muscle antibodies; if AChR antibodies are negative, consider muscle-specific kinase and lipoprotein-related 4 antibodies 3
- Conduct electrodiagnostic studies, including neuromuscular junction testing with repetitive stimulation and/or jitter studies 1
- Evaluate for possible concurrent myositis or myocarditis with CPK, aldolase, ESR, CRP, ECG, and TTE if respiratory insufficiency or elevated CPK/troponin T is present 1
Immediate Management
- Admit patient to ICU for close monitoring and potential respiratory support 1
- Initiate either IVIG (0.4 g/kg/day for 5 days for a total dose of 2 g/kg) or plasmapheresis for 5 days 1
- Continue corticosteroids if already prescribed (methylprednisolone 1-2 mg/kg daily) 1
- Perform frequent pulmonary function assessment and daily neurologic review 1
- Consider early intubation and mechanical ventilation if respiratory function deteriorates 4
Medication Management
- Maintain pyridostigmine therapy, adjusting dose based on improvement 1
- Strictly avoid medications that can worsen myasthenia: β-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolides 1, 5
- For patients already on immunosuppressive therapy (e.g., azathioprine, mycophenolate), continue these medications during crisis management 5
Comparative Efficacy of IVIG vs. Plasmapheresis
- Both IVIG and plasmapheresis are effective in treating myasthenic crisis 6, 7
- Some evidence suggests plasmapheresis may be more effective than IVIG in treating myasthenic crisis involving respiratory failure, though a definitive randomized trial is still needed 4
- The median time for disease stabilization is approximately 8 days with plasmapheresis and 10 days with IVIG 6
Management of Complications
- Ventilator-associated pneumonia is the most common complication (30% of cases) and should be aggressively treated 6
- Monitor for and address other complications such as deep vein thrombosis, sepsis, and cardiac arrhythmias 8
- Thymoma, elevated PCO₂ before mechanical ventilation, and pneumonia are independent risk factors for prolonged mechanical ventilation 8
Prognosis and Follow-up
- With appropriate treatment, mortality from myasthenic crisis has decreased from 75% historically to less than 5% currently 2
- The median duration of crisis is approximately 11 days, with median ICU stay of 15 days 6
- After crisis resolution, continue immunosuppressive therapy and gradually taper corticosteroids based on symptom improvement 1
- Consider thymectomy for patients with thymoma after stabilization, as thymoma is associated with poorer outcomes in myasthenic crisis 8
Special Considerations
- For patients with known myasthenia gravis undergoing surgery, consider preoperative plasma exchange or IVIG to minimize risk of postoperative myasthenic crisis 2
- MuSK-antibody positive patients may have shorter mechanical ventilation requirements and hospital stays compared to AChR-antibody positive patients 8
- Efgartigimod alfa-fcab may be considered for AChR-antibody positive patients who have inadequate response to conventional therapy 3, 9