2023 American Academy of Neurology Abstract Website

Objective:

To characterize lower extremity muscle fat fraction (MFF) in patients with myotonic dystrophy type 1 (DM1), myotonic dystrophy type 2 (DM2), and controls. Additionally, we examine the associations between MFF and disease-specific endpoints.

Background:

DM1 and DM2 are dominantly inherited muscular dystrophy primarily characterized by progressive muscle weakness, myotonia, and multisystemic features. A potential biomarker of disease severity includes MFF (%) derived from magnetic resonance imaging (MRI). However, how lower extremity MFF compares between DM1 and DM2 has not been previously examined against controls.

Design/Methods:

Lower extremity 3T MRIs were obtained using a two-point 3D Dixon volumetric interpolated breath-hold examination protocol. Muscle volumes (15mm thickness) were segmented from the proximal, middle, and distal levels of the thigh and calf in both legs. Lower extremity MFF was correlated with six-minute walk test (6MWT), grip strength, and 15-second step test using Spearman’s correlation (ρ). The sample consisted of seven patients with DM1(43% female), seven DM2 (86% female), and four controls (50% female).

Results:

Mean age was 50±13 years for DM1, 60±13 for DM2, and 56±8 for controls. Disease duration was 19±14 for DM1 and 18±14 years for DM2. Mean MFF of the thigh was 35.7% (range: 15.3%-79.9%) for DM1, 34.4% (17.8%-58.0%) for DM2, and 13.2% (10.5%-16.6%) for controls. Mean MFF of the calf was 32.9% (range: 17.9%-70.1%) for DM1, 27.3% (21.3%-34.6%) for DM2, and 12.6% (10.9%-14.9%) for controls. Higher MFF were strongly correlated with shorter distance of 6MWT (ρ=-0.74 for thigh and ρ=-0.64 for calf, p-value<0.01), weaker grip strength (ρ=-0.77 for thigh and calf, p-value<0.001), and less steps completed (ρ=-0.78 for thigh and ρ=-0.77 for calf, p-value<0.001). MFF were also moderately correlated with disease duration (p-value>0.5).

Conclusions:

Higher muscle fat infiltration of the lower extremities is associated with poorer physical performance and grip strength in both DM1 and DM2 groups.