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Myasthenic crisis is a life-threatening complication of myasthenia gravis characterized by severe muscle weakness affecting respiratory muscles, requiring immediate mechanical ventilation. It represents an acute exacerbation of the underlying autoimmune neuromuscular disorder, often triggered by infections, medications, or stress. This medical emergency has a mortality rate of 4-10% and requires prompt recognition and intensive care management.
Myasthenic crisis occurs due to severe dysfunction at the neuromuscular junction caused by autoantibodies against acetylcholine receptors or muscle-specific kinase (MuSK). These antibodies block, destroy, or alter acetylcholine receptors, preventing effective neuromuscular transmission and resulting in profound muscle weakness. The respiratory muscles become critically affected, leading to hypoventilation, hypoxemia, and potential respiratory failure requiring mechanical ventilation support.
Diagnosis involves recognizing the triad of worsening muscle weakness, respiratory compromise, and difficulty clearing secretions in a patient with known or suspected myasthenia gravis. Key clinical features include dyspnea, weak cough, dysarthria, dysphagia, and ptosis, with forced vital capacity typically less than 20 mL/kg indicating need for intubation. Management focuses on respiratory support, plasmapheresis or IVIG for rapid improvement, corticosteroids for long-term control, and identifying/treating precipitating factors while avoiding neuromuscular blocking agents.