MYOTONIC DYSTROPHY: EP.238 Masseter muscle volume as a disease marker in adult-onset myotonic dystrophy type 1

Abstract

Myotonic dystrophy type 1 (DM1) is an autosomal dominant genetic condition characterized by multisystem involvement. Given the recent commencement of clinical trials in DM1, reliable outcome measures assessing different disease manifestations need to be investigated and validated, while keeping the total number of assessments to a minimum. In this study we used magnetic resonance (MR) images of the head of DM1 patients from a previous study to investigate the clinical correlations of masseter muscle volume and evaluate its potential use as a marker of muscle involvement. Data from 39 DM1 patients and 20 age-matched control participants who had previously undergone MR imaging of the head, completed a range of clinical outcome measures and had CTG repeat measured by small-pool PCR was used. Single rater performed manual segmentation of each masseter muscle in all participants to estimate its volume. The masseter muscle was atrophied in DM1 patients when compared to controls (p<0.001). Significant correlations were discovered between masseter volume and genetic determinants of disease severity, including estimated progenitor allele length (p=0.001) and modal allele length (p=0.003), as well as the disease duration (p=0.009). After correction for lean body mass, masseter volume was inversely correlated with self-reported myotonia (p=0.014), and with muscle function quantified using the muscle impairment rating scale (p=0.008). Masseter muscle atrophy is common in DM1 patients, and is easily quantified on MRI. The masseter volume correlates with genetic determinants of disease and measures of muscle involvement, suggesting these changes reflect the underlying disease process. Further studies evaluating masseter muscle through quantitative MRI methods may yield useful insights for outcome measure selection, and demonstrate that data regarding both central and peripheral disease may be gained from MRI brain in DM1 patients.