Araya Puwanant

Introduction/Aims Although muscle structure measures from magnetic resonance imaging (MRI) have been used to assess disease severity in muscular dystrophies, little is known about how these measures are affected in myotonic dystrophy type 2 (DM2). We aim to characterize lower extremity muscle fat fraction (MFF) as a potential biomarker of disease severity, and evaluate its relationship with motor performance in DM2. Methods 3‐Tesla MRIs were obtained from nine patients with DM2 and six controls using a T1W‐Dixon protocol. To calculate MFF, muscle volumes were segmented from proximal, middle, and distal regions of the thigh and calf. Associations between MFF and motor performance were calculated using Spearman's correlations ( ρ ). Results Mean age of DM2 participants was 62 ± 11 y (89% female), and mean symptom duration was 20 ± 12 y. Compared to controls, the DM2 group had significantly higher MFF in the thigh and the calf segments ( p ‐value = .002). The highest MFF at the thigh in DM2 was located in the posterior compartment (39.7 ± 12.9%) and at the calf was the lateral compartment (31.5 ± 8.7%). In the DM2 group, we found a strong correlation between the posterior thigh MFF and the 6‐min walk test ( ρ = −.90, p ‐value = .001). The lateral calf MFF was also strongly correlated with the step test ( ρ = −0.82, p ‐value = .006). Discussion Our pilot data suggest a potential correlation between lower extremity MFF and some motor performance tests in DM2. Longitudinal studies with larger sample sizes are required to validate MFF as a marker of disease severity in DM2.