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 Ł1 liter, negative inspiratory force Ł20 cm H2O, or requirement of mechanical ventilation.Results:Out of 51 MG patients with respiratory failure, 7(14%) patients had no previous diagnosis of MG. Another patient was identified after the review. The mean age of these 8 patients was 56 years (range 23–76 years); six were women. Five had previous episodes of unexplained respiratory failure. On initial evaluation, ocular or bulbar signs were present in 7 patients. The diagnosis of MG was made by edrophonium test (n=3), edrophonium test with positive acetylcholine antibody levels or repetitive nerve stimulation (n=2), repetitive nerve stimulation with positive acetylcholine antibody levels (n=2), and positive acetylcholine antibody levels alone (n=1). Seven patients required mechanical ventilation. Plasma exchange (n=7) or intravenous immunoglobulins (n=1) resulted in successful extubation or resolution of symptoms in all patients.Conclusions:Respiratory failure can occur at presentation in MG. A high index of suspicion should be maintained in patients with previous history of unexplained respiratory failures.

Keywords: Myasthenia Gravis - diagnosis, Respiratory Insufficiency - diagnosis, Myasthenia Gravis - diagnosis, Respiratory Insufficiency - diagnosis