Fixed dynamometry is more sensitive than vital capacity or ALS rating scale

Introduction: Improved outcome measures are essential to efficiently screen the growing number of potential amyotrophic lateral sclerosis (ALS) therapies. Methods: This longitudinal study of 100 (70 male) participants with ALS compared Accurate Test of Limb Isometric Strength (ATLIS), using a fixed, wireless load cell, with ALS Functional Rating Scale-Revised (ALSFRS-R) and vital capacity (VC). Results: Participants enrolled at 5 U.S. sites. Data were analyzed from 66 participants with complete ATLIS, ALSFRS-R, and VC data over at least 3 visits. Change in ATLIS was less variable both within- and among-person than change in ALSFRS-R or VC. Additionally, participants who had normal ALSFRS-R arm and leg function averaged 12 to 32% below expected strength values measured by ATLIS. Conclusions: ATLIS was more sensitive to change than ALSFRS-R or VC and could decrease sample size requirements by approximately one-third. The ability of ATLIS to detect prefunctional change has potential value in early trials.