Features of repetitive nerve stimulation and nerve conduction studies in patients with amyotrophic lateral sclerosis

Abstract

AbstractBackgroundPrecise diagnosis of amyotrophic lateral sclerosis (ALS) and differential diagnosis between ALS and other diseases are important. For ALS diagnosis, not only needle electromyography but also decremental responses to repetitive nerve stimulation (RNS) and a decreased abductor pollicis brevis (APB)/abductor digiti minimi (ADM) amplitude ratio in nerve conduction studies (NCS) are useful. We should know the incidence of decrement in RNS responses and the decreased amplitude ratio in NCS in ALS patients with upper limb symptoms.AimsTo evaluate the findings of both tests in ALS patients with and without upper limb symptoms.MethodsWe selected consecutive ALS patients at our hospital from September 2016 to December 2020 who underwent RNS and NCS. RNS was performed on at least one of the following five muscles: APB, ADM, trapezius, deltoid, and/or frontalis.ResultsForty‐seven patients were included in this study. The rate of abnormal examination results was 70% for RNS responses, 49% for NCS, and 78% for at least one of the two tests in patients with upper limb symptoms at the time of RNS; by contrast, the rate was 30% for RNS responses, 20% for NCS, and 40% for at least one test in patients without upper limb symptoms at the time of RNS. RNS abnormalities were more often observed in patients with upper limb symptoms than in those without upper limb symptoms at the time of RNS (p = 0.030).ConclusionUpper limb symptoms at the time of RNS may reflect the rate of abnormal RNS responses in ALS.