P.16 - Relationships between ambulatory function and body composition in patients with Duchenne muscular dystrophy

Abstract

Ambulatory function is highly variable in Duchenne muscular dystrophy (DMD), even among boys of the same age. In addition, variations in total body mass and lean body mass are typical, and reflect growth as well as muscle atrophy. We measured the extent to which body composition can explain variability in ambulatory function in boys with DMD aged 5–20 years. Associations were measured at concurrent assessments of total body mass, % lean body mass (measured via DEXA) and ambulatory function using Pearson correlations and multivariable regressions accounting for repeated measures. A total of 327 patients were studied at n = 1453 visits with DEXA scans and ambulatory assessments. Percent lean body mass decreased with age, with means (standard deviations) of 75 (4), 74 (6), 68 (9), 60 (10) and 53 (10) for patients aged <6, 6–8, 8–10, 10–12, and >12 years, respectively. Associations between function and % lean body mass were numerically stronger than associations between function and age, with Pearson correlations of 0.59 and -0.32 for the North Star Ambulatory Assessment (NSAA) total score, −0.45 and 0.33 for the 30-ft walk/run, −0.42 and 0.37 for sit to stand and -0.38 and 0.25 for the 4-stair climb. In multivariable analyses adjusted for age and total body mass, each 10 point decrease in % lean body mass was associated with 5.4 units lower NSAA score, 1.7 seconds longer 30-ft walk/run, 2.5 seconds longer sit to stand and 1.5 seconds longer 4-stair climb (all p < 0.05). Accounting for % lean body mass, in addition to age and total body mass, more than doubled the proportion of explained variation in most functional measures, with levels of explained variation reaching 19–37%. We conclude that lean body mass is an important determinant of multiple components of ambulatory function. These findings can contribute to the interpretation of treatment effects on ambulatory outcomes, especially for treatments that aim to impact muscle mass and/or function.