D.P.15 Quantitative T2 relaxation times in lower leg of Duchenne and Becker muscular dystrophy patients

Abstract

Edema can be present in muscles of Duchenne muscular dystrophy (DMD) patients, and is thought to indicate inflammation. It can be quantified using MRI and could be useful as a marker of the disease progression in therapeutic trials. In this study, we compared edema in muscles of DMD patients, Becker muscular dystrophy (BMD) patients, and healthy controls. Edema was assessed in eight lower leg muscles of 19 DMD patients (10±3y, range 5–14y) and nine BMD patients (38±11y, range 26–63y) by measuring the T2 relaxation time using fat suppressed MRI at 3T (multi-echo sequence with seven echo times: 13–91ms). T2 values were obtained using manually drawn ROIs. T2 relaxation times in both DMD (mean 45ms) and BMD (mean 45ms) were higher than in healthy controls. As high fat fractions could still influence T2 relaxation times despite the application of fat suppression, we only included muscles with less than 20% fat (assessed by Dixon MRI) in the final analysis This did not alter the range and showed means of 42ms in DMD and 43ms in BMD. Surprisingly, muscles in DMD and BMD had similar T2 values. The only exception was tibialis anterior (TA) muscle. In patients younger than 10years the T2 relaxation time of this muscle was increased in both DMD (n=8) and BMD patients (50 vs 58ms). In DMD patients above the age of 10 the T2 of the TA was significantly lower than in BMD patients, contrary to what one might expect. These results suggest that edema, as defined by increased T2 relaxation times, is more pronounced in relatively mildly affected muscle tissue, and specifically the TA muscle in BMD patients and DMD patients under 10. Therefore, the use of quantitative T2 for disease evaluation or effects of therapy needs further study before it can be used routinely in trials in DMD patients.