What is the management approach for a myasthenia gravis crisis?

Management of Myasthenia Gravis Crisis

The management of myasthenia gravis crisis requires immediate hospitalization with ICU-level monitoring, administration of corticosteroids, and initiation of either intravenous immunoglobulin (IVIG) or plasmapheresis to rapidly reduce antibody levels. 1

Definition and Recognition

• Myasthenic crisis is defined as respiratory failure requiring mechanical ventilation in patients with myasthenia gravis 2
• Characterized by worsening muscle weakness affecting respiratory and/or bulbar muscles leading to respiratory compromise 3
• May be the presenting feature of myasthenia gravis or occur in known patients, typically within the first year of diagnosis 4

Initial Assessment and Stabilization

• Perform immediate pulmonary function assessment with negative inspiratory force (NIF) and vital capacity (VC) measurements 1
• Early intubation and mechanical ventilation is the most important initial step in management when respiratory failure is present 2
• Consider non-invasive ventilation (NIV) in selected patients with APACHE II score <6 and serum bicarbonate <30 mmol/L 5
• Monitor maximal expiratory pressure (Pemax) - values ≥40 cmH₂O predict successful extubation 5

Diagnostic Workup

• Check acetylcholine receptor (AChR) antibodies and anti-striated muscle antibodies 1
• If AChR antibodies are negative, test for muscle-specific kinase (MuSK) and lipoprotein-related protein 4 (LRP4) antibodies 1
• Measure CPK, aldolase, ESR, and CRP to evaluate for concurrent myositis 1
• Perform cardiac evaluation with ECG and transthoracic echocardiogram if respiratory insufficiency or elevated CPK/troponin T to rule out concurrent myocarditis 1
• Consider MRI of brain and/or spine to exclude CNS involvement or alternative diagnoses 1
• Obtain neurology consultation and electrodiagnostic studies (repetitive stimulation and/or jitter studies) 1

Treatment Algorithm

First-Line Interventions

• Respiratory Support

  • Admit to ICU for close monitoring 1
  • Perform frequent pulmonary function assessments 1
  • Initiate mechanical ventilation when indicated 2

• Immunotherapy (initiate immediately)

  • Administer high-dose corticosteroids: methylprednisolone 1-2 mg/kg/day IV or prednisone 1-1.5 mg/kg/day orally 1
  • Start plasmapheresis (5 sessions over 5 days) OR IVIG (2 g/kg total dose over 5 days at 0.4 g/kg/day) 1
  • Plasmapheresis may be more effective than IVIG when respiratory failure is present 2

• Cholinesterase Inhibitors

  • Pyridostigmine starting at 30 mg orally three times daily, gradually increasing to maximum of 120 mg four times daily as tolerated 1
  • Wean based on symptom improvement 1

Medication Precautions

• IMMEDIATELY discontinue medications that can worsen myasthenia gravis:
  • Beta-blockers
  • IV magnesium (absolutely contraindicated)
  • Fluoroquinolones
  • Aminoglycosides
  • Macrolide antibiotics 1, 6

Monitoring and Follow-up

• Daily neurological evaluation 1
• Frequent assessment of respiratory function 1
• Monitor for complications of immunotherapy 1
• Begin steroid taper 3-4 weeks after initiation, based on symptom improvement 1

Special Considerations

• Myasthenic crisis has a mortality rate of 4-8% with modern neurocritical care 7, 3
• For patients requiring mechanical ventilation, extubation failure occurs in approximately 39% of cases, most commonly due to poor cough strength 5
• ICPi-associated myasthenia gravis may be monophasic, potentially requiring less prolonged immunosuppression 1
• If severe hypomagnesemia requires treatment, neurology consultation is mandatory before administration 6

Treatment Response and Prognosis

• With appropriate management, mortality has decreased from historical rates of 75% to current rates of less than 5% 4
• Extubation failure is associated with significant in-hospital morbidity 5
• Most patients recover with timely respiratory support and appropriate immunotherapy 4