Six-Minute Walk Test demonstrates motor fatigue in spinal muscular atrophy

Abstract

Background: In spinal muscular atrophy (SMA), weakness, decreased endurance, and fatigue limit mobility. Scales have been developed to measure function across the wide spectrum of disease severity. However, these scales typically are observer dependent, and scores are based on sums across Likert-scaled items. The Six-Minute Walk Test (6MWT) is an objective, easily administered, and standardized evaluation of functional exercise capacity that has been proven reliable in other neurologic disorders and in children.

Methods: To study the performance of the 6MWT in SMA, 18 ambulatory participants were evaluated in a cross-sectional study. Clinical measures were 6MWT, 10-m walk/run, Hammersmith Functional Motor Scale-Expanded (HFMSE), forced vital capacity, and handheld dynamometry. Associations between the 6MWT total distance and other outcomes were analyzed using Spearman correlation coefficients. A paired t test was used to compare the mean distance walked in the first and sixth minutes.

Results: The 6MWT was associated with the HFMSE score (r = 0.83, p < 0.0001), 10-m walk/run (r = -0.87, p < 0.0001), and knee flexor strength (r = 0.62, p = 0.01). Gait velocity decreased during successive minutes in nearly all participants. The average first minute distance (57.5 m) was significantly more than the sixth minute distance (48 m) (p = 0.0003).

Conclusion: The Six-Minute Walk Test (6MWT) can be safely performed in ambulatory patients with spinal muscular atrophy (SMA), correlates with established outcome measures, and is sensitive to fatigue-related changes. The 6MWT is a promising candidate outcome measure for clinical trials in ambulatory subjects with SMA.

Figure Percent change in average velocity for each minute during the Six-Minute Walk Test Percent change in average velocity for each minute compared with the average velocity walked in the first minute during the Six-Minute Walk Test (6MWT) for spinal muscular atrophy (SMA) types 3a and 3b. The average velocity for each minute walked during the 6MWT decreased when compared with the average velocity walked in the first minute for participants with type 3a and 3b. Participants with SMA type 3a had slower average velocities at each minute.