Background: Myotonic dystrophy Type 1 is the most common form of adult muscular dystrophy, resulting in both motor and cognitive deficits. Whether these deficits progress or are stable requires further elucidation in natural history studies. Cognition in particular is challenging to study given the multiple domains and tests available for measurement.
Methods: We performed a literature review of all existing longitudinal studies of cognition in DM1 from 1993 to 2021. Studies were then separated by pediatric vs. adult findings and by test domain (memory, executive function, attention/processing speed, visuospatial construction, language, global intelligence).
Results: We identified seven adult and two pediatric studies of longitudinal cognitive function in DM1. All studies had a >5-year time between baseline and follow up. Among affected adults, in two of three studies which assessed episodic memory, this declined. Only one study assessed story recall, which also declined. Results were mixed for all other domains depending on the study and type of test. Affected children, especially those with congenital onset (CDM), had delays in language and global intelligence compared to peers, but did not regress.
Conclusions: Natural history studies of cognitive change in DM1 are limited and include studies with >5- year intervals. Pediatric studies were especially limited, but, in the existing two studies, children with CDM showed language and global delays and did not regress. In adults, memory was a domain of cognitive function which declined in multiple studies with various tests. However, other cognitive domains had mixed results within and across studies depending on the test employed and median age of participants at baseline. Based on these studies, formation of a uniform cognitive battery to be tested in longitudinal studies with shorter retest intervals and would provide valuable information for future treatment trials in DM1.