Jitter analysis with concentric needle electrodes in the extensor digitorum communis for the diagnosis of myasthenia gravis: a pilot study:

Bedside and laboratory diagnostic testing in myasthenia

Myasthenia gravis (MG) and congenital myasthenic syndromes (CMS) are a group of disorders with a well characterised autoimmune or genetic and neurophysiological basis. We reviewed the literature from the last 20 years assessing the utility of various neurophysiological, immunological, provocative and genetic tests in MG and CMS. Diagnostic sensitivity of repetitive nerve stimulation test ranges between 14 and 94% and specificity between 73 and 100%; sensitivity of single-fibre EMG (SFEMG) test ranges between 64 and 100% and specificity between 22 and 100%; anti-acetylcholine receptor (AChR) antibody sensitivity ranges from 13 to 97% and specificity ranges from 95 to 100%. Overall, SFEMG has the highest sensitivity while positive anti-AChR antibodies have the highest specificity. Newer testing strategies that have been investigated over the last couple of decades include ocular vestibular-evoked myogenic potentials, otoacoustic emissions and disease-specific circulating miRNAs in serum for autoimmune myasthenia, as well as next-generation sequencing for genetic testing of CMS. While there has been significant progress in developing newer testing strategies for diagnosing MG and CMS over the last couple of decades, more research is needed to assess the utility of these newer tools regarding their sensitivity and specificity.

Single-fiber EMG with concentric electrodes in lambert-eaton myasthenia

INTRODUCTION

We analyzed jitter recordings made with concentric needle electrode (CNE) single-fiber electromyography (SFEMG) in Lambert-Eaton myasthenia (LEM).

METHODS

Fifteen subjects diagnosed with LEM were studied using CNE-SFEMG in the extensor digitorum (ED) and tibialis anterior (TA) muscles. CNE-SFEMG in the ED and TA was also used to evaluate 12 and 10 healthy controls (HCs), respectively.

RESULTS

Ten men and 5 women were diagnosed with LEM based on an increase of 100% in compound muscle action potential amplitude during 50 Hz repetitive nerve stimulation. All patients exhibited markedly greater jitter in the ED (88.8 ± 23.2 µs) and TA (92.2 ± 30.2 µs) than HCs (28.3 ± 3.4 µs and 30.9 ± 5.1 µs, respectively).

CONCLUSIONS

CNE-SFEMG is sensitive for discovering abnormalities in neuromuscular transmission in LEM. Muscle Nerve 56: 253-257, 2017.