Ocular myasthenia gravis: Predictive value of single fiber electromyography

Extraocular muscle weakness is the most common presenting sign of myastheni a gravis (MG). More than half of patients presenting with symptoms isolated to these muscles (OMG) develop generalized myasthenia gravis (GMG) over th e course of their illness, No clinical, laboratory, or electrophysiological features are recognized that identify these highrisk patients. We have the refore assessed the ability of single-fiber electromyography (SFEMG) to pre dict the development of GMG in patients presenting with OMG. Thirty-nine co nsecutive patients presenting with OMG underwent SFEMG of the extensor digi torum communis muscle as well as a battery of other laboratory and imaging studies at the time of diagnosis. Ail patients were followed prospectively for a minimum of 24 months or until they developed GMG. Two patients were e xcluded, leaving 37 for assessment. Twenty remained with pure OMG for the e ntire follow-up period (mean, 55 months). Twenty-six of the 37 had abnormal SFEMG studies at presentation. Eleven of these remained with OMG and 15 de veloped GMG. Fifty-eight percent of patients with an abnormal SFEMG develop ed GMG, whereas 82% of those with a normal study remained with OMG. Thus, a normal SFEMG was associated with MG remaining restricted to the extraocula r muscles. (P = 0.036, Fisher's exact test), but an abnormal SFEMG was not predictive of subsequent development of GMG. (C) 1999 John Wiley & Sons, In c.