G.P.124: Increase in T2 relaxation times in skeletal muscle of Duchenne but not Becker muscular dystrophy patients

Abstract

Exon-skipping drugs in Duchenne muscular dystrophy (DMD) aim to ameliorate the phenotype by restoring truncated dystrophin expression. This potentially leads to a milder phenotype like Becker muscular dystrophy (BMD). This treatment development emphasizes the importance of quantitative outcome parameters and a better understanding of disease progression in both DMD and BMD. Quantitative mapping of T2 relaxation time using MRI can be used to assess muscle edema, but can also be influenced by fatty infiltration, even after fat suppression (FS). We performed quantitative T2 mapping with FS and quantitative Dixon MRI in lower leg muscles of DMD and BMD patients, and healthy controls. Outcome parameters were fat percentage and T2 relaxation time for seven lower leg muscles after controlling for fatty infiltration. The relation between T2 relaxation time and fat percentage was assessed and T2 values were compared between patients and controls for both DMD and BMD patients using an ANCOVA with disease status as fixed factor and fat percentage as covariate. We included 18 DMD boys, 11 healthy boys, seven BMD patients and nine healthy adults. There was a significant correlation between T2 relaxation time and fat percentage in DMD and BMD patients (<i>p</i><0.001), but not in healthy controls (<i>p</i>=0.15). After adjusting for fat, the T2 relaxation time was significantly increased in all DMD muscles (<i>p</i><0.01), except for the extensor digitorum longus muscle (<i>p</i>=0.71) compared to controls. In BMD patients, none of the muscles showed an increase in T2 relaxation time compared to controls. The increased T2 relaxation time in DMD, but not in BMD patients suggests that T2 relaxation time could be a useful outcome parameter in DMD trials. The correlation between fat percentage and T2 relaxation time in patients suggests that, despite FS, fatty infiltration still influences T2 values. This should be accounted for when using quantitative T2 mapping to investigate edema or inflammation.