The degree of muscle involvement of lower leg muscles of 34 patients with DMD >8 years, using muscle MRI, was estimated in a multicenter study at the Institute of Child Health and other centers in London, in the UK, and 1 in Rome, Italy. Muscle MRI findings in a subgroup of 15 patients were correlated with the histology of open biopsies of extensor digitorum brevis (EDB). A gradient of muscle involvement in the lower leg was documented in all patients, and the posterior compartment (gastrocnemius > soleus) was most severely affected. The anterior compartment (tibialis anterior/posterior, popliteus, extensor digitorum) was least affected. Muscle MRI/EDB involvement correlated with the patient’s age (p=0.055). MRI correlated with EDB histopathologic changes in 10/15 patients. Abnormal MRI grades 3-4 (range 0-4) were associated with more severe fibro-adipose tissue replacement. Muscle MRI showed a progressive involvement of the EDB, more obvious in older patients and those nonambulant for a longer time. [1]

COMMENT. This study demonstrates good correlation between muscle MRI and muscle histologic changes in boys with DMD. It validates muscle MRI as a tool for selection of patients with sufficiently preserved EDB muscle for clinical trials of IM injections of an antisense oligonucleotide (AO) to induce dystrophin production.