Impaired neuromuscular transmission in facial muscles of amyotrophic lateral sclerosis: A single‐fiber electromyography study

Abstract

AbstractBackgroundDecremental responses in repetitive nerve stimulation studies have been reported in the limb muscles of patients with amyotrophic lateral sclerosis (ALS).AimTo reveal the function of neuromuscular junction (NMJ) in the frontalis muscle, which is less affected in ALS.MethodsWe performed axonal‐stimulated single‐fiber EMG studies in the frontalis muscles in 27 patients with ALS, 32 with myasthenia gravis (MG), and 12 healthy controls were performed.ResultsThe mean value of mean consecutive difference (MCD) in ALS was greater than controls (P < .05), but smaller than MG (P < .01) [ALS; 26.5, MG;47.7, control;16.4 (µs)]. The percentage of endplates with increased jitter (MCD >51μs) in ALS was also greater than controls (P < .001) but smaller than MG (P < .001) [ALS; 7.7, MG; 29.4, control; 0.8 (%)]. In ALS, the mean MCD was negatively correlated with the bulbar subset of ALS functional rating scale revised (ALSFRS‐R) (r = −0.67, P < .01). No axonal blocking was observed in all cohorts. In the facial muscles that are relatively preserved in ALS, jitter in single‐fiber EMG was significantly increased, possibly caused by dysfunction of the presynaptic NMJ and motor nerve terminals.ConclusionsAssessment of neuromuscular transmission could provide a new insight into the pathophysiology of motor nerve terminal dysfunction in ALS.