Myotonic dystrophy type 1: a comparison between the adult- and late-onset subtype

INTRODUCTION/AIMS: While the extent of muscle weakness and organ complications has not been well-studied in patients with late-onset myotonic dystrophy type 1 (DM1), adult-onset DM1 is associated with severe muscle involvement and possible life threatening cardiac and respiratory complications. This study aimed to compare the clinical phenotype of adult-onset versus late-onset DM1, focusing on the prevalence of cardiac, respiratory and muscular involvement.

METHODS: Data was prospectively collected in the Dutch DM1 registry.

RESULTS: 275 adult-onset and 66 late-onset DM1 patients were included. Conduction delay on electrocardiogram was present in 123 out of 275 (45%) adult-onset patients, compared to 24 out of 66 (36%) late-onset patients (p=0.218). DM1 subtype did not predict presence of conduction delay (OR 0.706, CI 0.405-1.230, p=0.219). Subtype did predict indication for non-invasive ventilation (NIV) (late-onset vs. adult-onset, OR 0.254, CI 0.104-0.617, p=0.002) and 17% of late-onset patients required NIV compared to 40% of adult-onset patients. Muscular impairment rating scale (MIRS) scores were significantly different between subtypes (MIRS 1-3 in 66% of adult-onset vs. 100% of late-onset(p<0.001)), as were DM1-ActivC scores (67±21 in adult-onset vs. 87±15 in late-onset, p<0.001).

DISCUSSION: Although muscular phenotype was milder in late-onset compared to adult-onset DM1, the prevalence of conduction delay was comparable. Moreover, subtype was unable to predict the presence of cardiac conduction delay. Even though adult-onset patients had an increased risk of having an NIV indication, 17% of late-onset patients required NIV. Despite different muscular phenotypes, screening for multi-organ involvement should be equally thorough in late-onset as in adult-onset DM1. This article is protected by copyright. All rights reserved.