Elemental EM: Myasthenia Gravis

This is the first post in the Elemental EM series, a rapid review of core emergency medicine topics. The goal is to present high yield facts as a foundation for practice and fundamentals for board review. Please enjoy the following bullet point summary on myasthenia gravis.

Author: Courtney Cassella, MD (@Corablacas, EM Resident Physician, Icahn SoM at Mount Sinai) // Edited by: Alex Koyfman, MD (@EMHighAK, EM Attending Physician, UT Southwestern Medical Center / Parkland Memorial Hospital) and Brit Long, MD (@long_brit)


Source: http://www.myasthenia.asia/news.aspx?category=1
  • 0.15-0.7% of the population, Most often 3rd to 6th decade
  • Autoimmune: Acetylcholine receptor antibodies
    • Causes receptor degradation, dysfunction, and blockade
    • Impairs function at neuromuscular junction (NMJ) → decreased muscle strength
  • Dysfunction of thymus gland or immune response to infectious antigens → abnormal thymus → often thymoma present

Clinical Presentation

  • General weakness
    • Proximal muscles
    • Neck extensors
    • Facial or bulbar muscles: Ptosis, diplopia, dysphagia, dysarthria, dysphonia
  • Worsens: as the day progresses, with prolonged muscle use, hot temperatures, stress, infection
  • No deficit in sensory, reflex, or cerebellar function
  • Myasthenic crisis: Respiratory failure
    • Precipitants: infection, surgery, rapid tapering of immunosuppressants, pain, menstruation, pregnancy, sleep deprivation, medications
  • Evaluation for impending respiratory failure
    • Inspiratory function
      • Vital capacity <1L (<20-25 mL/kg)
      • Negative inspiratory force <20 cm H2O
      • Accessory muscle use
    • Expiratory function
      • Positive expiratory force <40 cmH2O
      • Weak cough
      • Difficulty counting to 20 in a single breath
    • Upper airway (bulbar) weakness: dysphagia, nasal regurgitation, nasal quality of speech, staccato speech, jaw weakness, bifacial paresis, tongue weakness

Differential Diagnosis

Lambert-Eaton SyndromeBotulismIntracranial mass
Drug-induced myasthenia gravisThyroid disordersStroke
Congenital myasthenia gravisElectrolyte imbalanceSepsis


  • Serologic testing – acetylcholine receptor antibodies
  • Ice pack test – ptosis improves with ice pack application
  • Edrophonium or neostigmine (Acetylcholinesterase inhibitor) → improves muscle strength
    • Limited use in testing as may worsen weakness in other NMJ disorders or cholinergic crisis leading to respiratory failure.
    • Caution: cardiac disease → may cause bradycardia, AV block, atrial fibrillation, cardiac arrest
    • Differentiates myasthenic crisis versus cholinergic crisis
  • Electromyographic testing → postsynaptic NMJ dysfunction


  • Neurology consult
Acetylcholinesterase Inhibitors (Adult Dosing)
Pyridostigmine Neostigmine
  • PO 60 – 90 mg every 4 hours
  • IV slow infusion 1/30th PO dose (2-3mg)
  • If a dose is missed, next dose is doubled
  • PO 15 mg
  • IV 0.5 mg
  • IM/SC 0.5 to 2.0 mg, onset 30 min, effect 4 hrs
  • Management of respiratory failure
    • Induction with smaller doses: Etomidate, fentanyl, propofol
    • Avoid use of depolarizing or nondepolarizing paralytic agents
      • If paralytics are necessary → half-dose
    • Immunosuppression: steroids, azathioprine, mycophenolate, plasma exchange, IVIG
    • Thymectomy


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