Myasthenia Crisis

Myasthenia crisis is a complication of myasthenia gravis. It is defined as worsening of myasthenic weakness requiring intubation or noninvasive ventilation. Myasthenia crisis has a mortality rate of 5%


  • Myasthenia crisis is a complication of myasthenia gravis
  • Defined as worsening of myasthenic weakness requiring intubation or noninvasive ventilation
  • Myasthenia crisis has a mortality rate of 5%
  • 10 to 20% of myasthenia gravis patients experience myasthenic crisis at least once in their lifetime

Cholinergic crisis

  • Paradoxical weakening with anticholinesterase medications is called "cholinergic crisis."
  • It can be difficult to distinguish from worsening myasthenia gravis.
  • Develops as a result of overstimulation of nicotinic and muscarinic receptors at the neuromuscular junctions and synapses
  • It is a major side effect of excessive anticholinesterase medication if the dose limitation of pyridostigmine is exceeded above 120 mg every three hours. .


  • concurrent infection
  • post-surgical intervention (eg, thymectomy)
  • pregnancy
  • childbirth
  • tapering of immunosuppressive medications
  • Certain drugs

Table 1: Other causes of acute neuromuscular respiratory failure

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Table 2: Drugs that precipitate myasthenia gravis

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  • Admit in ICU for frequent monitoring of respiratory function
  • Vital capacity (VC) and/or maximal inspiratory pressure (MIP) should be measured frequently, typically every four hours.
  • Diaphragm thickness measurements by using ultrasound
  • Elective intubation if suspecting impending respiratory failure
  • Dyspnea on lying down that can be expressed as suffocation or drowning.
  • Severe dysphagia with weak cough and difficulty clearing secretions.
  • Signs of respiratory muscle weakness, such as hypophonia, pausing during speech to take a breath, poor respiratory effort, increased respiratory rate with shallow breaths, use of accessory muscles of respiration, and paradoxical abdominal breathing. However the signs of respiratory muscle weakness not always apparent.
  • VC falls below 15 to 20 mL/kg
  • MIP is less negative than -25 to -30 cmH20
  • Decreased diaphragm thickening fraction
  • Progressive respiratory acidosis despite therapy
  • Arterial blood gases are insensitive tests to measure respiratory muscle weakness because they often develop only after the onset of life-threatening respiratory failure
  • For patients with myasthenic crisis who are intubated, anticholinesterase medications used for myasthenia gravis (eg, pyridostigmine) should be withdrawn to reduce airway secretions. These medications can be restarted at a low dose after the patient has shown a response to plasma exchange (PLEX) or intravenous immune globulin (IVIG).
  • Rapid therapy with PLEX or IVIG
  • Expert consensus suggests that PLEX is more effective and works more quickly. The choice between the 2 therapies depends on patient comorbidity (e.g., PLEX cannot be used in sepsis and IVIg is contraindicated in hypercoagulable states, renal failure, or hypersensitivity to immunoglobulin) and other factors, including availability.
  • Plasma exchange directly removes acetylcholine receptor antibodies from the circulation
  • Generally the course of treatment consists of five exchanges (3 to 5 L of plasma each) over 7 to 14 days
  • Dosage of IVIG is 2 g/kg, usually over 2-5 days.
  • Concurrent initiation of chronic immunomodulating therapy with high-dose glucocorticoids; if glucocorticoids are contraindicated or less effective consider azathioprine, mycophenolate mofetil, or cyclosporine.
  • Weaning from mechanical ventilation with spontaneous breathing trials considered after treatment with plasma exchange or IVIG has been started and respiratory muscle strength has been improved (VC >15 to 20 mL/kg and a MIP more negative than -25 to -30 cmH2O)
  • Remove any precipitating factors such as drugs or infections exacerbating the disease.
  • Workup for concurrent infections including CBC, UA, CXR and blood cultures.
  • Treat any infection if present
  • IV Magnesium added as allergy

Mechanical Ventilation in Myasthenia Crisis

  • The key to the greatest chance of recovery in patients with neuromuscular disease is quick assessment and prompt treatment.
  • Identifying patient with impending respiratory failure and prompt endotracheal intubation with positive pressure mechanical ventilation should be considered while managing myasthenia crisis
  • Invasive mechanical ventilation has the advantage of adequate secretion clearance and full support for those suspected to have prolonged courses of crisis
  • The mode of mechanical ventilation generally utilized for managing myasthenia crisis is assist control modes of volume controlled ventilation and low levels of positive end-expiratory pressure (PEEP) with subsequent adjustments.
  • The median duration of mechanical ventilation is 14 days in myasthenia crisis

Complications of Myasthenia crisis

  • Fever and infection, including pneumonia, bronchitis, urinary tract infection, colitis caused by Clostridium difficile, bacteremia, and sepsis.
  • Increased risk for vascular complications including deep vein thrombosis, heart failure, acute myocardial infarction, cardiac arrhythmias, and cardiac arrest.

Further Reading

  • Excellent Review Article - Getting Rid of Weakness in the ICU: An Updated Approach to the Acute Management of Myasthenia Gravis and Guillain-Barré Syndrome (Lizarraga, Lizarraga, & Benatar, 2016)


  • Boon, A. J., Harper, C.J., et al. Two-dimensional ultrasound imaging of the diaphragm: quantitative values in normal subjects. Muscle Nerve. 2013;47(6):884-889
  • Sanders, D. B., Wolfe, G. I., Benatar, M., et al. International consensus guidance for management of myasthenia gravis: Executive summary. Neurology 2016; 87:419.
  • Lizarraga, A. A., Lizarraga, K. J., & Benatar, M. (2016). Getting Rid of Weakness in the ICU: An Updated Approach to the Acute Management of Myasthenia Gravis and Guillain-Barré Syndrome. Seminars in Neurology, 36(6), 615–624.
  • Weinberg, M., Cavalcante, J. A., Choy, T., & Ahmad, S. (2019). A 23-Year-Old Man With Dyspnea During Myasthenia Crisis. Chest, 155(6), e155–e157.