Six-Minute Walk Test as a Measure of Walking Capacity in Ambulatory Individuals With Amyotrophic Lateral Sclerosis

Abstract Objective To determine the validity of the 6-minute walk test (6MWT) as an outcome measure to evaluate walking capacity in ambulatory patients with amyotrophic lateral sclerosis (ALS). Design Observational study. Setting Multidisciplinary ALS clinic at an academic medical center. Participants Patients with ALS (N=186) who ambulate without (stage I) or with (stage II) an assistive device. Interventions Not applicable. Main Outcome Measure Walking distance obtained from the 6MWT. Results Participants performed the 6MWT, 25-foot walk test (25FWT), Timed Up and Go (TUG) test, lower extremity maximum voluntary isometric contraction (MVIC), ALS Functional Rating Scale-Revised (ALSFRS-R), and forced vital capacity (FVC). Walking capacity was reduced to 66% predicted of healthy subjects (75.2%±22% in stage I; 42.6%±22% in stage II). The 6MWT correlated with all other outcome measures in ambulatory patients with ALS (25FWT: r =−.74, P ≤.0001; TUG test: r =−.80, P ≤.0001; MVIC: r =.64, P ≤.0001; percent predicted FVC: r =.25, P ≤.0007; ALSFRS-R: r =.52, P ≤.0001; ALSFRS-R gross motor subscore: r =.71, P ≤.0001). When ambulatory patients with ALS were stratified by stage of ambulation, the 6MWT was associated with all other outcome measures in stage I (25FWT: r =−.56, P ≤.0001; TUG test: r =−.66, P ≤.0001; MVIC: r =.51, P ≤.0001; percent predicted FVC: r =.40, P ≤.02; ALSFRS-R: r =.52, P ≤.0001; ALSFRS-R gross motor subscore: r =.61, P ≤.0001). In stage II, the 6MWT correlated with the 25FWT ( r =−.83, P ≤.0001), TUG test ( r =−.77, P ≤.0001), MVIC ( r =.47, P ≤.0001), and ALSFRS gross motor subscore ( r =.61, P ≤.0001), but not with percent predicted FVC ( r =.09, P ≤.513) or ALSFRS-R ( r =.21, P ≤.141). Conclusions The 6MWT is a valid measure of walking capacity of ambulatory patients with ALS that is associated with measures of lower extremity muscle strength and function in both stages of ambulation. The discordance between the 6MWT with the ALSFRS-R and percent predicted FVC in stage II ambulatory patients with ALS indicates that the 6MWT is an independent measure of ambulatory function in both stages of ambulation. The 6MWT may provide a quantitative, simple, and inexpensive outcome measure of walking capacity for early stage clinical trials in ambulatory patients with ALS.