Distal Motor Latency in Amyotrophic Lateral Sclerosis: A Robust and Reliable Prognostic Marker

An electrophysiological test is routinely done to confirm Amyotrophic Lateral Sclerosis (ALS) and rule out differentials. Distal Motor Latency (DML) is a simple electrophysiological measure that is always done in a primary setting. It can be used as an excellent prognostic marker for ALS so that we can know ALS better and formulate precise management plans. This longitudinal study was conducted in the Neurology Department of Bangladesh Medical University (BMU), Dhaka, Bangladesh from April 2022 to October 2023. In this study a total of 34 subjects, 17 ALS patients with normal DML and 17 ALS patients with prolonged DML, were enrolled. Severity was assessed by the ALS functional rating scale-revised (ALSFRS-R). The study's endpoints were determined as death during this 6-month follow-up or reaching an advanced stage (ALSFRS-R <20). Then, an electrophysiological test was used to measure DML in all four commonly tested nerves. ALSFRS-R was significantly reduced (p<0.025) at 6 months in ALS patients with prolonged DML than normal DML. It was found that having a higher odd (p<0.012, OR=20.718), prolonged DML had a significant impact on the outcome of ALS patients than that of normal DML. In multivariate analysis, lower ALSFRS-R at diagnosis (B= -0.124, p<0.001, HR=0.883) and prolonged DML (B=1.412, p<0.031, HR=4.104) were associated with poor outcomes. ALS patients with prolonged DML also had a poorer prognosis than patients with normal DML (log-rank test, p<0.045). In this study, patients with prolonged DML had a significant functional decline, rapid disease progression and poor prognosis than patients with normal DML. So, prolonged DML can be used as a robust prognostic marker for patients with ALS.