CMAP decrement by low-frequency repetitive nerve stimulation in different hand muscles of ALS patients

To study compound muscle action potential (CMAP) decrement by low-frequency repetitive nerve stimulation (RNS) in different hand muscles of amyotrophic lateral sclerosis (ALS) patients and the relationship with split hand phenomenon and clinical manifestation.

Clinical and decrement data of 51 ALS patients who had done RNS in different hand muscles were retrospectively reviewed from November 2016 to July 2017. Decrement data of 24 myasthenia gravis (MG) and 20 Lambert Eaton myasthenia syndrome (LEMS) patients was also reviewed to compare decrement pattern with hand muscles of ALS patients.

There was statistical significance between the decrement ratio of abductor digiti minimi (ADM) and abductor pollicis brevis (APB) as well as ADM and first dorsal interosseous (FDI). The decrements of the APB, ADM, and FDI were negatively correlated with their amplitude of CMAPs respectively. The difference between the decrement ratio of the APB and ADM was negatively correlated with the division ratio (CMAP_APB/CMAP_ADM). The decrement ratio of APB and FDI was negatively correlated with their muscle strength. There was a mild correlation between decrement ratio of APB and disease course. There was no statistical significance in the decrement pattern of the three-hand muscles of ALS patients. There was statistical significance in decrement pattern between APB of ALS and LEMS patients.

Dysfunction of neuromuscular transmission was found in hand muscles of ALS patients, APB was involved most significantly. The dysfunction of neuromuscular transmission might be involved in the formation of the split hand phenomenon.