T77. Reference values for jitter recordings with concentric needle electrodes on stimulated frontalis

Introduction Single fiber electromyography (SFEMG) serves as the most sensitive technique to assess neuromuscular transmission (NMT). In recent years, disposable concentric needle electrodes (CNE) become an alternative to single fiber electrodes for recordings because of concerns about the risk of transmitting infections. Reference values for this new method should be established first before its clinical use in differential diagnosis of neuromuscular junction disorders. Methods We recruited 73 patients, 32 males and 41 females (18–83 years, mean age 52.2 ± 14.0 years), with eyelid, ocular, or weakness symptoms other than myasthenia gravis (MG). None of them had neuromuscular junction diseases, facial nerve palsy or myopathies. The facial nerve was stimulated at the temporal branch with surface electrodes. CNE recorded 20 apparent single fiber action potentials (ASFAPs) from the frontalis for each subjects. Jitter was measured with amplitude level trigger method and expressed as the mean consecutive difference (MCD). Results The mean MCD were 17.68 ± 3.30  μ s for subjects and 17.66 ± 7.81  μ s for individual potentials. For ensuring higher specificity, we set the mean values plus 3 SD as the upper normal limits, and figured out the corresponding cut-offs of 28  μ s for mean jitter values and 42  μ s for jitter values of individual potentials. Conclusion Our data derived from disease control subjects are similar to those of previous studies by other authors on healthy controls. It is a helpful supplement to the reference value pool of CNE-SFEMG of the frontalis. Introducing patients with confusing diseases into the reference population will increase the ability of this technique to differentiate MG from non-NMT disorders.