Individualized Prediction of Changes in 6-Minute Walk Distance for Patients with Duchenne Muscular Dystrophy. Goemans N*, Vanden Hauwe M, Signorovitch J, Swallow E, Song J; Collaborative Trajectory Analysis Project (cTAP). PLoS One. 2016 Oct 13;11(10):e0164684. doi: 10.1371/journal.pone.0164684. eCollection 2016

1 University Hospitals Leuven, Child Neurology, Leuven, Belgium, 2 Analysis Group, Inc., 111 Huntington Ave, 14th floor, Boston, Massachusetts, United States of America, 3 The Trajectory Analysis Project (TAP) Collaboration, One Broadway, 14th floor, Cambridge, Massachusetts, United States of America

Membership of the cTAP is provided in the Acknowledgments.

* nathalie.goemans@uzleuven.be

ABSTRACT

Background
Deficits in ambulatory function progress at heterogeneous rates among individuals with Duchenne muscular dystrophy (DMD). The resulting inherent variability in ambulatory outcomes has complicated the design of drug efficacy trials and clouded the interpretation of trial results. We developed a prediction model for 1-year change in the six minute walk distance (6MWD) among DMD patients, and compared its predictive value to that of commonly used prognostic factors (age, baseline 6MWD, and steroid use).

Methods
Natural history data were collected from DMD patients at routine follow up visits approxi- mately every 6 months over the course of 2–5 years. Assessments included ambulatory function and steroid use. The annualized change in 6MWD (Δ6MWD) was studied between all pairs of visits separated by 8–16 months. Prediction models were developed using multi- variable regression for repeated measures, and evaluated using cross-validation.

Results
Among n = 191 follow-up intervals (n = 39 boys), mean starting age was 9.4 years, mean starting 6MWD was 351.8 meters, and 75% had received steroids for at least one year. Over the subsequent 8–16 months, mean Δ6MWD was -37.0 meters with a standard deviation (SD) of 93.7 meters. Predictions based on a composite of age, baseline 6MWD, and steroid use explained 28% of variation in Δ6MWD (R2 = 0.28, residual SD = 79.4 meters). A broadened prognostic model, adding timed 10-meter walk/run, 4-stair climb, and rise from supine, as well as height and weight, significantly improved prediction, explaining 59% of variation in Δ6MWD after cross-validation (R2 = 0.59, residual SD = 59.7 meters).