S150. Detection of upper motor neuron impairment in ALS with central motor conduction time

Introduction Detection of both upper and lower motor neuron impairments is essential for making a diagnosis of amyotrophic lateral sclerosis (ALS). Although electrophysiological findings identifying lower motor neuron damage have been established, there are few useful objective biomarkers for upper motor neuron impairment. Here, we retrospectively investigated the utility of the central motor conduction time (CMCT) for the detection of upper motor neuron impairment in patients with ALS. Methods Fifty-five patients were diagnosed as ALS from 2007 to 2017 in our hospital. Forty-five ALS patients without any signal changes in the pyramidal tracts on magnetic resonance images and 10 healthy controls participated in this study. Electromyograms were recorded from the first dorsal interosseous and tibialis anterior muscles. Transcranial magnetic stimulation and magnetic motor root stimulation were performed to measure cortical and root latencies and obtained the CMCT. ALS patients were classified into two subgroups; positive and negative Babinski’s sign. The cortical and motor root latencies and CMCT were compared between two subgroups. Finally, we calculated the rates of ALS patients with abnormally prolonged CMCT (longer than mean +2 standard deviation of normal values). Results Cortical latency, motor root latency and CMCT were significantly longer in ALS group than the control group. There were no differences in the latencies and CMCT between the two subgroups of ALS patients. The CMCT was abnormally prolonged in 60% of ALS patients with positive Babinski’s sign and 50% of those with negative Babinski’s sign, respectively. Conclusion The CMCT is useful for detecting upper motor neuron impairment in patients with ALS without any clinical pyramidal signs. CMCT can pave the way for finding upper motor neuron impairment masked by lower motor neuron damage in ALS patients.