Table of Contents
Primary Category
Neuromuscular
P-Category
Secondary Category
S-Category
Authors:
Introduction
- 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. .
Precipitants
- concurrent infection
- post-surgical intervention (eg, thymectomy)
- pregnancy
- childbirth
- tapering of immunosuppressive medications
- Certain drugs
Table 1: Other causes of acute neuromuscular respiratory failure
Table 2: Drugs that precipitate myasthenia gravis
Management
- 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crisis who are intubated, anticholinesterase medications used for myasthenia gravis (eg, pyridostigmine) should be withdrawn to reduce airway secretions.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)
- Case Discussion - A 23-Year-Old Man With Dyspnea During Myasthenia Crisis (Weinberg, Cavalcante, Choy, & Ahmad, 2019)
Bibliography
- 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 https://doi.org/10.1002/mus.23702
- Sanders, D. B., Wolfe, G. I., Benatar, M., et al. International consensus guidance for management of myasthenia gravis: Executive summary. Neurology 2016; 87:419. https://doi.org/10.1212/WNL.0000000000002790
- 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. https://doi.org/10.1055/s-0036-1592106
- 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. https://doi.org/10.1016/j.chest.2018.10.054
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Written by
Movement Disorders Neurologists and teaches physicians internationally, Directs an online mini-fellowship in Movement Disorders since 2017, Founding director of the International Neurology program at University of Nebraska Medical Center