Background

• As many as 20% of patients with myasthenia gravis experience crisis
• Crisis can be initial manifestation of disease
• Respiratory failure is feared complication

Clinical Presentation of Respiratory Failure in MG Patient

• Increasing weakness (bulbar/proximal extremity/neck)
• Dyspnea usually worse in supine position (increased dependence of diaphragm on gravity)
• Important to remember that patients may not exhibit normal signs of respiratory failure secondary to weakness (ex: accessory muscle use)

Causes

• medication noncompliance
• infection
• surgery
• pregnancy/child birth
• drugs (antibiotics, cardiovascular, anesthetics, anticonvulsants, antipsychotics, etc.)

Management

• Most Important Step = Assessment/Monitoring of Respiratory Function
• Vital Capacity (VC) and Max Inspiratory Pressure (aka Negative Inspiratory Force) are most important to monitor during crisis
• Consider intubation if VC below 15-20 ml/kg OR MIP/NIF less negative than -25 to -30 cmH2O
• Often need ICU for frequent monitoring, q2-4 hr respiratory function testing
• Plasma Exchange OR IVIG (rapid acting therapies)
• Glucocorticoids: crisis patients often started on high dose steroids
• Associated with transient worsening of weakness, however less of a concern with concurrent plasma exchange/IVIG
• Stay tuned next week for intubation pearls!

References

Bird S, Levine J. “Myasthenic Crisis.” UpToDate. 25 August 2016; https://www.uptodate.com/contents/myasthenic-crisis?source=search_result...

Tintinalli, JE. Tintinalli's Emergency Medicine: A Comprehensive Study Guide. 8th ed. NewYork, NY: McGraw-Hill Education LLC, 2016.