A Dutch team compared the muscular, respiratory and cardiac phenotype of 275 people with classic myotonic dystrophy type 1 (DM1) (median age of onset: 25 years) with that of 66 people with a late-onset form (median age of onset: 50 years). The study shows that:
- 40% of the patients with classic form and 17% of those with late form used non-invasive ventilation.
- All late-onset patients had a low Muscular Impairment Rating Scale (MIRS) score (no muscle damage or distal muscle damage), while 66% of those with classic form had proximal and distal muscle damage (high MIRS score).
- conduction disorders were present on the electrocardiogram in 36% of late-onset forms (24 participants) and 45% of adult forms (123 participants), while only 34 people had clinical cardiac manifestations.
- the presence of conduction disorders was correlated with age and MIRS score, but not with the type of DM1 form, classic or late.
The authors conclude that it is important to follow up late-onset forms of DM1, particularly cardiological ones, even in the absence of cardiac symptoms.
