Stimulated single-fiber EMG of the frontalis and orbicularis oculi muscles in ocular myasthenia gravis

We performed single-fiber electromyography by axonal stimulation (stimulated SFEMG) of the frontalis and orbicularis oculi muscles of 20 patients with ocular myasthenia gravis (OM) and 46 controls. In controls, mean consecutive differences (MCD) ranged from 5 to 55 μs (average, 14.7 ± 2.8 μs) in the frontalis and from 4 to 56 μs (average, 12.56 ± 2.19 μs) in orbicularis oculi. The mean MCD of individual muscle potentials (MPs) was 14.6 ± 6.8 μs in frontalis and 12.68 ± 6.10 μs in orbicularis oculi. In the OM patients, the mean MCD was 43.85 ± 25.18 μs in the frontalis and 69.85 ± 29.55 μs in orbicularis oculi (P < 0.0001), and the number of MPs with altered MCD was 7.15 ± 4.66 (range, 1–18) and 12.65 ± 4.90 (range, 6–21), respectively (P < 0.0001). We conclude that stimulated SFEMG of the orbicularis oculi muscle is more sensitive for the diagnosis of OM than of the frontalis muscle. Muscle Nerve 28: 501–503, 2003