Myotonic dystrophy type 1 (DM1) is an autosomal dominant multisystemic disease that affects muscular and extra-muscular systems, including the central nervous system. Brain damage in DM1 is associated with subtle cognitive and behavioural disorders, with a major impact on socio-professional adaptation.
This French study, involving clinicians from the Institute of Myology, included 28 adult patients with DM1 (mean age: 46 years) and 18 age- and sex-matched healthy controls.
Comprehensive neuropsychological tests were conducted for all patients, focusing on frontal lobe neuropsychology (motivation, social cognition and executive functions). Among them, 18 DM1 patients and 18 healthy controls underwent brain MRI.
The neuropsychological evaluation showed that :
- most patients showed significant impairment in frontal executive functions (auditory working memory, inhibition, contextualisation and mental flexibility) ;
- patients showed only minor difficulties in social cognition tests.
Neuroimaging analysis revealed :
- atrophy mainly in the parahippocampal and hippocampal regions and, to a lesser extent, in the basal ganglia ;
- the correlation between social cognition scores and atrophy in the right parahippocampal gyrus.
The results of this study show that social dysfunction in DM1 may be the consequence of cognitive impairment in mental flexibility and social contextualisation rather than a specific deficit in social cognition such as emotion recognition.
The authors suggest that white matter lesions and grey matter disease could explain this social dysfunction, involving in particular the frontal-subcortical network and the hippocampal/parahippocampal regions, brain regions known to integrate contextualisation and navigation, respectively.
