What is the treatment for a possible myasthenia gravis crisis?

Treatment for Myasthenia Gravis Crisis

Myasthenia gravis crisis requires immediate respiratory support and immunomodulatory therapy, with plasmapheresis or IVIG as first-line treatments to rapidly reduce autoantibodies and improve neuromuscular function.

Immediate Management

Respiratory Support

• Assess respiratory function immediately using:

  • Negative Inspiratory Force (NIF) measurements (normal values > -60 cm H2O) 1
  • Forced Vital Capacity (FVC) - values <80% predicted with symptoms or <50% without symptoms indicate respiratory compromise 1
  • Peak Cough Flow (PCF) - values <270 L/min indicate impaired ability to clear secretions 1

• Intubation criteria:

  • Early intubation is essential if bulbar symptoms with aspiration risk and/or respiratory insufficiency are present 2
  • Do not delay intubation if respiratory parameters are deteriorating rapidly
  • Secure airway before respiratory failure becomes critical

Medication Management

1. Cholinesterase inhibitors:

   • Temporarily discontinue pyridostigmine during acute crisis phase if patient is intubated 1
   • Once stabilized, resume pyridostigmine at 30 mg orally three times daily, gradually increasing to maximum 120 mg four times daily 1, 3
   • IV neostigmine may be used if oral administration is not possible 1

2. Acute immunomodulatory therapy (initiate immediately):

   • First-line options:

     • Plasmapheresis: 5-6 exchanges over 10-14 days 1, 2, 4
     • OR
     • IVIG: 2 g/kg divided over 5 days 1, 4

   • Plasmapheresis is generally preferred for faster onset of action (24-48 hours) compared to IVIG (4-5 days) 4

Concurrent Management

Identify and Treat Precipitating Factors

• Common triggers that must be addressed 2, 4:
  • Respiratory infections (most common)
  • Aspiration
  • Sepsis
  • Recent surgery
  • Rapid tapering of immunosuppressants
  • Recent initiation of corticosteroids
  • Medications that worsen neuromuscular blockade

Avoid Medications That Worsen MG

• Strictly avoid:
  • β-blockers
  • IV magnesium
  • Fluoroquinolones
  • Aminoglycosides
  • Macrolides
  • Methocarbamol
  • Orphenadrine
  • Neuromuscular blocking agents (especially atracurium, mivacurium, and succinylcholine) 1

Aggressive Respiratory Care

• Implement intensive respiratory therapy to reduce complications:
  • Regular suctioning
  • Chest physiotherapy
  • Intermittent positive-pressure breathing
  • Bronchodilator treatments when indicated 5
  • Aggressive respiratory treatment significantly reduces atelectasis and pneumonia (46% vs 91% in less aggressive approaches) 5

Initiation of Long-term Immunosuppression

1. Corticosteroids:

   • Begin prednisone 0.5-1.5 mg/kg orally daily 1
   • Note: Initial steroid therapy may temporarily worsen symptoms in some patients

2. Steroid-sparing agents (start concurrently with steroids):

   • Azathioprine: 2 mg/kg of ideal body weight in divided doses
   • OR
   • Mycophenolate mofetil: Start 500 mg twice daily, increase to 1000 mg twice daily
   • OR
   • Methotrexate: 15 mg weekly 1

Monitoring and Follow-up

• Monitor in ICU setting for at least 24 hours after stabilization 2

• Regular assessment of:

  • Respiratory parameters (NIF, FVC)
  • Bulbar function (swallowing, speech)
  • Muscle strength
  • Signs of infection or other complications 1, 6

• Typical duration of mechanical ventilation is approximately 2 weeks (median 12-14 days), but can be longer with complications 2

• Approximately 20% of patients remain ventilated after 1 month 2

Special Considerations

• Risk of recurrence: Lifetime risk of crisis recurrence is approximately 30% 2
• Mortality: 2-5% (rarely from crisis itself, but from complications) 2
• Prevention of future crises:
  • Maintain optimal immunosuppression
  • Regular neurological follow-up
  • Prompt treatment of respiratory infections
  • Avoid medications that exacerbate MG 1, 6

The aggressive management of myasthenic crisis with early respiratory support and immunomodulatory therapy has dramatically improved outcomes, reducing mortality from 75% to less than 5% over the past four decades 4.