Risk for generalization in ocular onset myasthenia gravis: experience from a neuro-ophthalmology clinic

Conversion to generalized myasthenia gravis (GMG) within the first 2 years has been reported in 18–85% of patients with ocular myasthenia gravis (OMG). The aim of the study was to investigate the risk factors for generalization in patients with OMG admitted to a neuro-ophthalmology clinic and to determine if there were differences between patients with GMG with predominant bulbar (GMG-B) or extremity muscle (GMG-E) involvement according to the 6th and 24th-month Myasthenia Gravis Foundation of America classification ranks. Patients with OMG who were followed-up for at least 24 months were retrospectively analyzed. Demographic, clinical, laboratory features and treatment strategies that can be associated with generalization and time to generalization were evaluated. Of the 139 patients with OMG, 54 (39%) showed generalization with a mean time of 10.3 (range 2–24) months. GMG-B and GMG-E were diagnosed in 31 (22.3%) and 23 patients (16.5%), respectively. Seropositivity for acetylcholine receptor and muscle-specific tyrosine kinase antibodies, abnormal single-fiber electromyography (SFEMG), and the presence of thymic abnormalities (thymoma and hyperplasia) were factors associated with generalization on multivariate analysis without a significant difference between the GMG-B and GMG-E groups. In addition, an abnormal repetitive nerve stimulation test was related to a shortened time to generalization. Bilateral ptosis at onset was found as a risk factor for generalization. In a neuro-ophthalmology clinic, bilateral ptosis as an initial feature of OMG must be approached cautiously because it may be the first sign of impending GMG.