Abstract

Saly. H. Elkholy *, Hatem. S. Shehata , Hebatallah Raafat , Amani. M. Nawito and Rania. A. Almahdy

This study was aimed at establishing normative values for volitional single fiber electromyography (SFEMG) of the masseter muscle in Egyptians and evaluating the sensitivity of this test in the diagnosis of generalized myasthenia gravis. Twenty two patients with myasthenia gravis (mean age of 37.72 years; range, 20 to 59; mean duration of illness, 4 years; range, 1 months to 16 years) where enrolled in the study to assess for SFEMG of the masseter muscle and of the extensor digitorum communis (EDC) muscle. Twenty normal individuals (mean age 34.3; range 22 to 55 years) where similarly studied to determine the normative values of SFEMG of the masseter muscle. The mean jitter of the masseter in the patients’ group was 63.4 ± 9.98 us, compared to 21.3 ± 4.9 us in the control group. Examination of the masseter muscle yielded 100% sensitivity in this study, compared to 90% sensitivity for EDC. We suggested a normal upper limit of masseter’s mean jitter of 26 microsecond/ study (mean +/- 1 SD) and 28 us / individual fiber pair (The 95th upper percentile was 27.51 us). Volitional SFEMG of the masseter muscle is highly sensitive test to diagnose generalized MG that is not related to weakness of this particular muscle but correlated to the degree of the disease’s severity.