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A comparison of the 6-minute walk test to commonly used outcome measures in Duchenne muscular dystrophy (DMD)

CM MCDONALD MD 1, EK HENRICSON MPH1,
C SPALDING MD 1, RT ABRESCH 1, J HAN 1,
A NICORICI 1, L ATKINSON 2, A REHA2, G ELFREING2,
L MILLER 2

1. Physical Medicine and Rehabilitation, UC Davis Medical Center, Sacramento, CA, USA;
2. PTC Therapeutics, Inc., South Plainfield, NJ, USA

Background/Objectives: The lack of functional outcome measures is an obstacle to the clinical development of new treatments for DMD. The six-minute walk test has been used extensively in other disease states to measure global physical functioning and is being used in DMD clinical trials. The objectives of this study is to evaluate the correlations between the 6-minute walk distance (6MWD) and other commonly used measures of disease severity in Duchenne muscular dystrophy.

Design: This is a single-center investigator-initiated observational study.

Participants and Setting: We enrolled ambulatory boys with DMD (n=17) and able-bodied controls (CTRL) (n=34) ages 4-12 years old.

Materials/Methods: Evaluations were conducted in our exercise physiology laboratory at baseline (all participants) and at Week 1 (DMD) participants only). Outcome measures included a modified 6MWT, timed motor function tests, Brooke & Vignos motor function scales, and isometric quantitative strength testing.

Results: There was a significant difference in outcome measure values between DMD and CTRL groups (p<0.001). In DMD, 6MWD had a strong negative correlation with time to climb 4 stairs, time to run/walk 10 meters, time to run/walk 25 meters (r=0.7 to -0.9), and was strongly correlated wit Vignos lower extremity functional scale (r=0.72). 6MWD had a moderate negative correlation (r=0.45-0.69) with time to stand from the supine position, and a moderate correlation with the Brooke upper extremity functional scale, and quantitative knee extensor strength. The 6MWD did not correlate with quantitative knee flexor strength. Correlations between 6MWD and other measures were not as strong in the CTRL group.

Conclusions/Significance: 6MWD shows moderate to strong correlation with timed measures of physical function in DMD. 6MWDE shows a strong correlation with the Vignos lower extremity motor function scale and a moderate correlation with the Brooke upper extremity motor function scale. The 6MWD correlates moderately with isometric knee extensor strength but not with knee flexor strength. The 6MWD measures global physical function and endurance in DMD and provided a quantitative outcome measure that is related to but different from commonly used measures of strength and functional ability.

 
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