Myasthenia Gravis

Myasthenia Gravis is a topic covered in the 5-Minute Emergency Consult.

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  • Antibody-mediated condition that results in painless, fatigable muscle weakness
  • Ocular or generalized:
    • Ocular (eyelids and extraocular) muscle weakness:
      • Most common initial symptom (60%)
      • ∼80% of myasthenia gravis (MG) patients who present with ocular weakness initially will progress to general weakness within 2 yr.
    • Generalized:
      • Usually affects proximal limbs, axial muscle groups such as neck, face, bulbar muscles
  • Acute or subacute, with relapses and remissions
  • Associated with thymoma in 15% and thymic hyperplasia in 65%
  • Myasthenic crisis:
    • Respiratory failure or inability to protect airway due to weakness
    • Triggers:
      • Infection
      • Surgery
      • Trauma
      • Pregnancy
      • Medication changes (e.g., rapid tapering of steroids)
    • Difficult to distinguish from cholinergic crisis resulting from excessive doses of acetylcholinesterase (AChE) inhibitors:
      • Cholinergic crisis may also include muscarinic effects such as sweating, lacrimation, salivation, and GI hyperactivity in addition to weakness.


  • Pediatric MG is rare and distinct:
    • Congenital MG: Genetic defect
    • Juvenile MG: Autoimmune disorder
    • Transient neonatal MG: Postdelivery complication from placental transfer of maternal antibodies
  • Adult MG has bimodal distribution:
    • 1st peak in 2nd and 3rd decades affecting mostly women
    • 2nd peak in 6th and 7th decades affecting men


  • Antibody-mediated attack on nicotinic acetylcholine receptors
  • Up to 20% of patients may be acetylcholine receptor antibody (AChR Ab) negative
  • Penicillamine can cause MG as well as other autoimmune conditions
  • Many medications may worsen myasthenic weakness:
    • Aminoglycosides, macrolides, quinolones, antimalarials
    • Local anesthetics
    • Antidysrhythmics (propafenone, quinidine, procainamide)
    • β-Blockers, calcium-channel blockers
    • Anticonvulsants (phenytoin, carbamazepine)
    • Antipsychotics (phenothiazine, atypicals)
    • Neuromuscular blocking agents
    • Iodine-containing radiocontrast

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