Myasthenia gravis

Definition

• A autoimmune disorder of the motor endplate that is associated with thymomas and causes a syndrome of weakness that worsens with repeated movements
• Can also present with predominantly bulbar involvement, or simple ocular involvement

Clinical Manifestations

• History
• Signs & Symptoms
  • Ptosis worse than baseline
  • Abnormal or fatiguable extraocular movements
  • Dysarthria
  • Neck flexion and extension (tests C3-4 that also innervates the diaphragm)
  • Decreased duration of limb raiding

Management

• Acute
  • Monitor FVC, MIPS, and MEPS
    • Can approximate FVC by counting the duration of exhilation
• Chronic

Avoidance of Certain Medications

• Some medications are thought to cause or exacerbate myasthenic crisis through a variety of mechanisms1
• Altered immune response:
  • Definite association with immune checkpoint inhibitors and D-penicillamine
  • Probable association with statins
  • Possible association with interferons
  • Doubtful association with tandutinib
• Effects on neuromuscular transmission:
  • Definite association with macrolides, aminoglycosides, class Ia antiarrhythmics, magnesium, neuromuscular blockers and inhaled anaesthetics, corticosteroids (use low doses when possible), botulinum toxin
  • Probable association with fluoroquinolones, penicillins (rare), lithium
  • Possible association with beta blockers, L-type CCBs, antipsychotics
• The above antibiotics can be used if necessary, but may need close clinical monitoring