Myasthenia Gravis Presenting as Sudden–onset Isolated Hypercapnic Respiratory Failure

Myasthenic crisis, which can be life-threatening due to severe respiratory failure, occurs in 15-20% of patients with myasthenia gravis. However, the crisis often develops within 1-2 years after diagnosis and is very rare as a first symptom of myasthenia gravis; isolated sudden-onset hypercapnic respiratory failure without other symptoms of myasthenia gravis is even rarer. A 63-year-old woman presented to the emergency department with fever and dizziness. Chest computed tomography showed multifocal peribronchial ground-glass opacities, and a diagnosis of pneumonia was made. Initially, the patient did not have dyspnea. However, she developed acute hypercapnic respiratory failure and was intubated. After mechanical ventilation, her hypercapnia improved initially, but worsened on initiation of weaning from the ventilator. As she had a high acetylcholine receptor antibody titer, myasthenia gravis was diagnosed. Her hypercapnia improved after treatment with pyridostigmine and methylprednisolone.