A new parameter to discriminate amyotrophic lateral sclerosis patients from healthy participants by motor cortical excitability changes.

Introduction: We sought a combination of abnormalities to define a more sensitive measure of cortical excitability in amyotrophic lateral sclerosis (ALS).

Methods: The automatic threshold tracking method was employed to assess the resting motor threshold, intracortical facilitation (ICF), short-interval intracortical inhibition (SICI), and short-interval intracortical faciilitation (SICF) in patients and controls.

Results: SICF at interstimulus intervals (ISI) between 1 and 1.8 ms and 2 and 3 ms as well as average SICI and SICI at ISIs of 1 and 2.5 ms were significantly reduced in ALS. The SICI curve was altered, displaying a solitary peak. Discriminant analysis revealed that the combination of SICI 2.5 ms and the mean SICF between 1 and 1.8 ms ISIs was the most sensitive parameter to distinguish patients with ALS from healthy participants.

Discussion: Along with the reduced SICI and its altered shape, connectivity between motor cortical circuits is changed in ALS. Combination with SICF increases the diagnostic utility of SICI in ALS.