What is the immediate management for a myasthenia gravis crisis?

Immediate Management of Myasthenia Gravis Crisis

In a myasthenia gravis crisis, immediate management requires hospital admission with ICU monitoring, airway protection, and prompt initiation of plasmapheresis as the preferred first-line immunotherapy. 1

Definition and Recognition

• Myasthenic crisis is defined as respiratory failure requiring mechanical ventilation due to myasthenic weakness
• Affects approximately 15-20% of MG patients, typically within the first 2-3 years of diagnosis 2
• Mortality has decreased from 75% historically to less than 5% with modern management 3

Initial Assessment and Stabilization

1. Respiratory Assessment

   • Monitor Negative Inspiratory Force (NIF) and Vital Capacity (VC)
   • NIF < -20 cm H₂O indicates severe respiratory compromise requiring immediate intervention
   • NIF between -20 to -60 cm H₂O requires close monitoring 1

2. Airway Management

   • Secure airway if respiratory failure is present or imminent
   • Consider intubation for patients with:
     • Severe bulbar weakness causing inability to protect airway
     • Progressive respiratory muscle weakness
     • Declining pulmonary function tests

Immediate Therapeutic Interventions

First-Line Treatment

• Plasmapheresis:

  • Preferred over IVIG for crisis due to faster onset of action
  • Typical regimen: 5 exchange sessions over 7-14 days 1, 2

• Alternative: IVIG

  • If plasmapheresis is unavailable
  • Dosage: 2 g/kg divided over 5 days 1

Supportive Care

• Discontinue cholinesterase inhibitors (e.g., pyridostigmine) during acute ventilatory support to reduce secretions
• Identify and treat precipitating factors:
  • Respiratory infections (most common trigger)
  • Aspiration
  • Sepsis
  • Medication changes (especially rapid steroid tapering)
  • Surgical procedures 3

Medication Considerations

• Avoid medications that exacerbate MG:

  • β-blockers
  • IV magnesium
  • Fluoroquinolones
  • Aminoglycosides
  • Macrolides 1

• If anesthesia is needed:

  • Safe options: Propofol, sevoflurane, isoflurane, fentanyl, remifentanil
  • Avoid: Atracurium, mivacurium, and succinylcholine
  • Preferred muscle relaxant: Rocuronium (can be reversed with sugammadex) 1

Ongoing Monitoring

• Continuous respiratory monitoring
• Serial measurements of NIF and VC
• Regular neurological assessments
• Monitor for complications:
  • Ventilator-associated pneumonia
  • Deep vein thrombosis
  • Pressure ulcers

Post-Crisis Management

• Once stabilized, initiate or adjust immunosuppressive therapy:
  • Corticosteroids (prednisone 1-1.5 mg/kg PO daily)
  • Consider steroid-sparing agents (azathioprine, mycophenolate mofetil, methotrexate)
• Gradually reintroduce cholinesterase inhibitors as patient improves

Common Pitfalls to Avoid

• Delaying immunotherapy while waiting for diagnostic confirmation
• Misinterpreting deterioration as cholinergic crisis (rare) rather than myasthenic crisis
• Failing to recognize and treat precipitating factors
• Premature extubation before adequate neuromuscular recovery
• Initiating high-dose corticosteroids without immunomodulatory coverage (may temporarily worsen symptoms)

Most patients with myasthenic crisis can be successfully weaned from mechanical ventilation within one month, and the condition generally has a favorable prognosis with proper management 2.