Respiratory failure as a first presentation of myasthenia gravis.

Background: Although respiratory failure commonly occurs during the course of myasthenia gravis (MG), it is rarely described at presentation in patients with previously unrecognized MG.

Material/methods: We determined the prevalence and clinical characteristics of patients with respiratory failure associated with undiagnosed MG by review of the medical records of all patients who were diagnosed with MG related respiratory failure at four University hospitals. Respiratory failure was defined on the basis of a forced vital capacity < or =1 liter, negative inspiratory force < or =20 cm H2O, or requirement of mechanical ventilation.