Cognitive decline over time in adults with myotonic dystrophy type 1: A 9-year longitudinal study

•Verbal memory, visual attention, and processing speed abilities decline overtime.•Progression in cognitive scores correlates with age and disease duration, not with nCTG, muscular impairment or education.•The rate of cognitive decline is higher among DM1 patients with the late-onset phenotype than in the adult phenotype.

Myotonic dystrophy type 1 (DM1) is an inherited neuromuscular disease with multisystemic involvement including the central nervous system. The evolution of the cognitive profile is a matter of debate, whether an eventual decline could be global or process-specific. Study aims are to describe, compare and document the clinical relevance of the progression of cognitive abilities in DM1 patients with adult and late-onset phenotypes. A total of 115 DM1 patients (90 adult; 25 late-onset) were assessed twice within a 9-year period on cognitive abilities (language, memory, visual attention, processing speed, visuoconstructive abilities and executive functions) and intellectual functioning (WAIS-R 7). A significant worsening over time was observed for verbal memory, visual attention, and processing speed. The progression in cognitive scores correlated with age and disease duration, but not with nCTG, muscular impairment nor education at baseline. Intellectual functioning remained stable. The rate of decline was higher among the late-onset phenotype than in the adult phenotype. Results showed that executive functions, language, and visual memory are impaired earlier in adult life, while verbal memory, visual attention, and processing speed decline later. Globally, results suggest an early and accelerated normal ageing process. This longitudinal study was based on the largest sample and the longest time period studied to date. These findings are highly relevant for clinical practice and genetic counselling.