P.195 Quantitative skeletal muscle MRI of golden retriever muscular dystrophy dogs

Abstract

Quantitative magnetic resonance imaging (MRI) is often proposed in clinical trials related to neuromuscular diseases. The intramuscular fat fraction (FF) is associated with functional decline while the quantification of water tissue relaxation times (T1 and T2) and the extracellular volume fraction (ECV) provides information about microstructural changes of the muscle tissue fraction that has not been replaced by fat. The Golden Retriever Muscular Dystrophy (GRMD) dog, an animal counterpart of Duchenne muscular dystrophy, represents an ideal model to evaluate the sensitivity to disease status and therapeutic response of these variables in a dystrophic context. MRI data from the pelvic limbs distal muscles of young and old GRMD (N = 14) and healthy dogs (N = 9) were acquired. A subgroup of the young GRMD dogs were under corticosteroids. The exam comprised water T2 mapping and T1 mapping before and after an intravenous injection of a gadolinium-based contrast agent from which ECV was calculated. In young dogs, we found that T1, T2 and ECV were significantly higher in all muscles of GRMD compared to healthy counterparts. Water T2 and ECV values were significantly lower in the corticosteroid compared to the naïve GRMD dogs. In old dogs, GRMD presented higher ECV values in all muscles. ECV classified dystrophic muscles with higher sensitivity and specificity than water T2 and native T1. Significant correlations were found between native T1 and water T2 in all the groups. Interestingly, ECV and water T2, as well as ECV and native T1 correlated significantly in all groups, except old GRMD dogs. In conclusion, native T1, water T2 and ECV measured by MRI are sensitive to the histological alterations encountered in dystrophic muscles. On a small cohort of GRMD dogs, the two latter variables were also sensitive to a corticosteroid treatment. By combining the different variables, we were able to distinguish different pathophysiological processes in young and old GRMD dogs.