P.95 - Skeletal muscle tissue characterization of a large cohort of patients with Becker muscular dystrophy using quantitative NMR imaging

Abstract

Becker muscular dystrophy (BMD) is a genetic disease caused by an X-linked recessive mutation leading to a defective dystrophin expression, with a relatively mild clinical course. Skeletal muscle fibers undergo degeneration and regeneration leading to a progressive muscle replacement by adipose tissue. This study was to characterize the skeletal muscles of a large cohort of BMD patients using quantitative NMR imaging. 86 BMD patients and 22 age-matched controls underwent NMR imaging of both thighs on a 3T scanner. Fat fraction was quantified using the 3-point Dixon method. Water T2 was measured with a multi spin echo sequence and a triexponential signal decay model. The different parameters were evaluated in 10 different regions of interest delineated in the left and right thighs. For all muscles, mean fat fraction was statistically higher in the patients group than in the controls (36 ± 12 % VS 3 ± 1 %, p < 0.05). Vastus lateralis, medialis and intermedius, as well as semi-tendinous and semi-membraneous muscles were the more affected. Mean fat fraction was correlated with patient age (R = 0.50, p < 0.05). Water T2 was slightly but statistically more elevated in the patients (36.0 ± 1.5 ms VS 35.2 ± 1.4 ms, p < 0.05), and associated standard deviations, which can be interpreted as an index of muscle tissue disorganization, were also statistically higher in this group (3.1 ± 0.5 ms VS 2.2 ± 0.3 ms, p < 0.05). This study partly confirms previous evaluation realized on smaller cohorts of BMD patients. The severity of muscle involvement was already shown to vary between muscle groups in the thighs. However, Wokke et al. did not detect any water T2 increase in the calves of a small group of BMD patients. Our much larger sample size certainly helped to pick up a slight water T2 increase in the thighs, which likely reflects the inflammatory processes occurring during the disease. A three-year follow up of these patients is on-going and will quantify the progression rate of skeletal muscle remodeling in BMD.