Lower limb muscle magnetic resonance imaging in myotonic dystrophy type 1 correlates with the six-minute walk test and CTG repeats

The aim of this study was to elucidate correlations among clinical, genetic, and magnetic resonance imaging (MRI) data of muscles in myotonic dystrophy type 1 (DM1). We retrospectively reviewed the medical records and images of nineteen patients with DM1 from different families. We retrieved the genetic data (CTG repeats) and the clinical data, which included disease duration, creatine kinase level, sum score of manual muscle testing, modified Medical Research Council sum score, and the six-minute walk test results (6MWT). The correlation analyses showed a statistically significant correlation between the modified Medical Research Council sum score and CTG repeat numbers. Among the lower extremity muscles, 6MWT correlated most with the sum of the ankle plantar-flexors (the soleus, medial, and lateral gastrocnemius muscles). Compared to the other plantar-flexor muscles, the soleus muscle presented the highest correlation with the 6MWT. Additionally, our results showed that the CTG repeat numbers did not correlate with the 6MWT. However, it correlated with the modified Medical Research Council sum score. The ankle plantar-flexor muscles were the most severely affected muscles revealed in the whole body MRI, and presented statistically significant correlation with the 6MWT. Among the plantar-flexor muscles, the soleus muscle most influenced the 6MWT.