Mechanism hypotheses for the electrophysiological manifestations of two cases of endplate acetylcholinesterase deficiency related congenital myasthenic syndrome

Abstract

Objective: To summarize the electrophysiological characteristics of two cases of endplate acetylcholinesterase deficiency (EAD) related congenital myasthenic syndrome (CMS) caused by COLQ mutation and to discuss the possible mechanism of these electrophysiological phenomena.

Methods: Electrophysiological examinations were conducted including nerve conduction studies, routine electromyography (EMG), repetitive nerve stimulation (RNS) and single fiber EMG (SFEMG). The ulnar nerve was also stimulated at 50 Hz followed by 0.5 Hz to record the recovery process of compound muscle action potential (CMAP).

Results: Repetitive CMAP (R-CMAP) was found in motor nerve conduction in both cases. Needle EMG showed myogenic damages and SFEMG showed remarkably increased jitter values. Of note, the amplitude of CMAP and R-CMAP showed regular changing trends, and so did their time intervals in RNS studies.

Conclusions: The change patterns of CMAP and R-CMAP, in combination with other electrophysiological features are very useful for the diagnosis of EAD related CMS, especially in predicting the presence of correct gene mutations.

Keywords: COLQ; Congenital myasthenic syndrome; Electromyography; Endplate acetylcholinesterase deficiency; Repetitive compound muscle action potential.