Abstract
Current therapies in Duchenne muscular dystrophy (DMD) include contracture management and glucocorticosteroids (GC) with timed tests being used to monitor progression and predict loss of ambulation. The objective is to understand the role of GC on contracture, progression and interplay between strength and contractures on timed velocity tests. Individuals were enrolled in the CINRG Duchenne natural history study at 20 sites obtained in a standardized manner. Data included: range of motion (ROM) in 4 joints (elbow (EE) and wrist (WE) extension, knee extension (KE) and ankle dorsiflexion(DF), timed tests (supine to stand, stairs, 10MWT), quantitative muscle testing (QMT) of knee flexors and extensors. We assessed EE and ankle DF ROM across the age span and over time. Longitudinal mixed effects models assessed the relationship between strength and ROM on velocity with age and GC status as covariates. We enrolled 440 individuals; mean baseline age was 10.7 +/-5.7 and 15.3 +/-6.6 at last study visit. At baseline, 292 were ambulatory; 192 at last study visit. Only 16% were GC naïve, 81% of cohort ranged from 6mos- 25 years on GCs. GCs have initial affect on ROM compared to steroid naïve and no significant effect on progression. QMT, ROM, age and GCs contribute to timed tests. KE strength and DF ROM are significant predictors of velocity for all timed function tests (p<.001). KE strength is the primary predictor of walking velocity estimating that every pound increase in KE results in a 0.042 m/s improvement in 10MWT and a smaller similar increase of .009m/s with every degree of ankle DF ROM. GC use provides an improvement in strength and ROM but does not affect rate of change. Knee strength have a greater influence on speed of timed tests than DF ROM although both are statistically significant predictors of velocity. Results show that retaining knee strength, along with management of contractures, are important to maintain the ability to run, climb, and stand.
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