300PThe role of muscle MRI in mild neuromuscular disorders. where are we?

There is increasing evidence that muscle magnetic resonance imaging (MRI) can be a valuable tool to improve the diagnostic workup of patients with inherited neuromuscular disorders (NMD), as it can also guide the genetic prioritization and the follow-up of patients as the disease progresses, or during clinical trials. In order to explore the sensitivity and specificity of muscle MRI for the early detection or confirmation of NMD, we selected all the patients who had come to our clinical attention for hyperckaemia/muscle weakness over the past two years and who had also undergone at least one muscle MRI study and exome sequencing. We selected 93 patients aged between 1 and 86 years. Of these, 32 received a conclusive diagnosis of NMD (34%), including 25 (78%) who had a muscle MRI consistent with the genetic disorder, and 7 who presented asymptomatic hyperckaemia and a negative MRI. Of these, 5 patients were associated with a heterozygous pathogenetic variant in RYR1, one harbored a heterozygous variant in MYH7 mutation, and one was a presymptomatic Pompe disease. Of the 93 patients, 28 had a positive MRI, 2 harbors VUS in large genes (COL6 and TTN), and one was negative. In 26/93 patients, the muscle MRI highlighted unspecific findings; these patients harbored heterozygous mutations in autosomal recessive genes or VUS in autosomal dominant genes. In 39/93 the muscle MRIs were negative and in 5 cases we reached a diagnosis of a different disorder. Twenty cases harbored VUS in large genes unrelated to their muscular picture (TTN, COL6, FLNC) and 7 carried only benign variants. The diagnostic rate, especially in mild cases of NMD, is compatible with what is described in literature. Muscle MRI was confirmed as an important tool in the work up of neuromuscular diseases, demonstrating a sensibility of 78% and a specificity of 100% (12 patients). A better definition of both morphological and functional techniques to improve biochemical and physiological imaging of skeletal muscle and their integration with analysis techniques on Big Data could be the answer to the gap in the use of MRI in mild NMD. This work was supported by an EU Horizon 2020 project grant termed “Computational Models for New Patient Stratification Strategies of Neuromuscular Disorders; ComPaSS-NMD” (Horizon2020 Project-ID 101080874).