Jitter Remains Stable Throughout a Single Fiber EMG Session in Healthy and Myasthenic Muscles

Abstract

Fatigability is the hallmark of myasthenia gravis (MG). It is not clear, however, whether there is an analogous increase in jitter during the course of a single fiber electromyography (SFEMG) session. The individual jitter values of all potentials of 76 normal and 44 myasthenic orbicularis oculi muscles were assigned a rank number according to their temporal order in which they were collected and linear regression was performed to determine if the slope of the regression line was significantly different from zero. Control and MG subjects displayed rather flat linear regression lines with non-significant positive or negative slopes. Accordingly, ROC analysis yielded areas under the curve near 0.5. We conclude that there is no systematic jitter increase during the collection of 20 potential pairs in a typical SFEMG session.

The dispersion of individual jitter values is a sensitive diagnostic indicator of voluntary SFEMG

“…[1][2][3] SFEMG becomes particularly important in the not uncommon clinical setting of seronegative myasthenia-like symptoms with normal repetitive nerve stimulation studies. In this respect, additional parameters that consider the course 4 and the variability of individual jitter values throughout a SFEMG session are particularly desirable, as they may help enhance diagnostic accuracy.…”

“…The diversity and lack of specificity of muscle pathology in IMNM is increasingly recognized and reported, and these cases further highlight the importance of interpreting the muscle biopsy with knowledge of the clinical context. 4 In addition, anti-HMGCR and anti-SRP antibodies have very low false positive and false negative rates, depending on the type of assay, and therefore the antibodies should also be interpreted in the appropriate clinical context. 5 In summary, we steadfastly agree with the authors on the importance of not missing the diagnosis of IMNM, due to its potential treatability.…”