Myasthenia gravis and myasthenia crisis:
Myasthenia gravis (MG) is a condition causing muscle weakness due to autoantibodies targeting the nicotinic acetylcholine receptors at the neuromuscular junction.
Myasthenia crisis is a complication of myasthenia gravis characterized by worsening muscle weakness, which can lead to respiratory failure that requires intubation and mechanical ventilation.
It is important to note that myasthenic crisis can be life-threatening, but with prompt and appropriate management, most patients can recover.
The priorities of management of myasthenic crisis in the emergency department include:
1. Airway management:
Patients with myasthenic crisis may require intubation and mechanical ventilation to support their breathing.
2. Identification and treatment of triggers:
Common triggers include infection, surgery, pregnancy, childbirth, or tapering of immunosuppressive medications.
3. Immunosuppressive therapy:
Corticosteroids or intravenous immunoglobulin can help to improve symptoms and prevent future crises.
4. Monitoring and supportive care:
Patients with myasthenic crisis require close monitoring and supportive care, including electrolyte management, nutritional support, and physical therapy.
Muscle relaxants or paralytic agents in MG.
Both succinylcholine and rocuronium act on the same acetylcholine receptors affected in MG.
Succinylcholine causes continuous depolarization, while rocuronium competitively antagonizes these receptors.
However, in myasthenia gravis, the reduced number of receptors can lead to resistance to succinylcholine and increased sensitivity to rocuronium.
Avoid succinylcholine in myasthenic crisis, if possible.
Succinylcholine may fail to work due to reduced acetylcholine receptor density on muscle.
Succinylcholine may also lead to unpredictable effectiveness and prolonged duration of action.
However, if succinylcholine is the only option available, an increased dose should be considered.
Rocuronium is the preferred paralytic agent in myasthenic crisis,
due to its competitive antagonism and a more predictable response in patients with myasthenia gravis.
The dose of rocuronium for myasthenia crisis should be reduced by approximately 50% compared to the usual dose.
The recommended dose is 0.3 to 0.5 milligram per kilogram based on expert consensus.
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