39K/23Na-MRI at 7T for assessment of ionic balance combined with fat quantification at 3T in myofibrillar myopathies

Motivation: Recent advances have enabled the application of 39K-MRI in skeletal muscle in vivo. Moreover, information on disease progression/pathogenesis from non-invasive 1H-MRI is still limited. Goal(s): Determination of apparent tissue potassium and tissue sodium concentrations (aTPC/aTSC) in myofibrillar myopathies. Approach: Less severe effected lower legs of 10 patients with filaminopathy-, desminopathy- and zaspopathy-causing mutations measured by 39K/23Na-MRI at 7T and Dixon-type-sequence at 3T. Results: Fat-corrected ion concentrations were significantly altered in calf muscles of all patients with myofibrillar myopathies in comparison to healthy control subjects. Despite incoherencies with respect to disease progression and etiology fat-corrected aTSC were in- and aTPC were decreased. Impact: Combined 39K/23Na-MRI detects changes in ionic balance beyond fatty replacement of muscle in a diverse cohort of myofibrillar myopathies. Further studies are needed to investigate whether different genotypes or whether disease progression can be detected in early stages by 39K/23Na-MRI.