Stimulated single fiber EMG of the frontalis muscle in the diagnosis of ocular myasthenia

We performed single fiber electromyography by axonal stimulation (SFEMG-AS) of the frontalis muscle of 16 patients with ocular myasthenia gravis (OM) and 33 controls. In the controls, values of mean consecutive differences (M CD) ranged from 5 to 55 mu s (average, 14.7 +/- 2.8 us) and mean MCD of ind ividual MPs was 14.6 +/- 6.8 mu s All the OM patients showed abnormal SFEMG -AS jitter before prostigmine was administered (mean MCD, 49.19 +/- 21.82 m u s, percentage of blocks: 20.97 +/- 18.53). Twenty or 30 min after prostig mine had been administered, we saw a significant improvement in jitter: mea n MCD was 36.38 +/- 22.49 mu s (P = 0.005), and percentage of blocks was 10 .16 +/- 18.87 (P = 0.008). The method was well tolerated. We conclude that SFEMG-AS of the frontalis muscle is a sensitive technique for the diagnosis of OM and is easy to carry out. (C) 2000 John Wiley & Sons. Inc.