Single fiber electromyography in the diagnosis of ocular myasthenia gravis: report of 90 cases.

BACKGROUND: The aim of this study was to evaluate single fiber electromyography (SFEMG) in the diagnosis of ocular myasthenia gravis (OMG), compared with repetitive nerve stimulation (RNS) and blood concentration of antibody to acetylcholine receptor (AchRAb).

METHODS: SFEMG, RNS and AchRAb titration were measured in 90 patients with OMG (44 men, 46 women).

RESULTS: Markedly increased jitter and ratio of block in the frontalis and the extensor digitorum communis (EDC) were observed (83.3% and 61.1%, respectively). The mean jitter was 43.6 +/- 14.5 micros, and the percentages of jitter>55 micros and blocking were 16.9% +/- 19% and 3.5% +/- 9.5% respectively in the EDC. The mean jitter was 64.3 +/- 25.6 micros, and the percentages of jitter > 55 micros and blocking were 33.5% +/- 27.6% and 29.3% +/- 23.2% respectively in the frontalis. The percentage of abnormal RNS was 27.8% (25/90). There was an increased AchRAb titration in 29 (32.2%) of the 90 patients. Increased jitter, blocking was negatively correlated with maximum decrement to RNS (P < 0.01). 11.4% (4/35) of patients with abnormal RNS and 24.1% (7/29) patients with abnormal AchRAb were seen in the patients with normal SFEMG in the EDC.

CONCLUSION: SFEMG test showed the highest sensitivity in the diagnosis of OMG. To our knowledge, the three methods (SFEMG, RNS and AchRAb) are complementary in the diagnosis and differential diagnosis of OMG.