Frontostriatal dysexecutive syndrome: a core cognitive feature of myotonic dystrophy type 2

The aim of this study was to assess cognitive status in a large group of patients with myotonic dystrophy type 2 (DM2) compared to type 1 (DM1) subjects matched for gender and age, using a comprehensive battery of neuropsychological tests. Thirty-four genetically confirmed adult DM2 patients were recruited and matched for gender and age with 34 adult-onset DM1 subjects. All patients underwent detailed classic pen and pencil neuropsychological investigation and also computerized automated battery-CANTAB. More than half of DM2 patients had abnormal results on executive tests [Intra/Extradimensional Set Shift (IED), Stockings of Cambridge (SOC)] and verbal episodic memory (Ray Auditory Verbal Learning Test). Regarding DM1, abnormal results in more than 50 % of subjects were achieved in even ten tests, including visuospatial, language, executive, cognitive screening and visual memory tests. Direct comparison between patient groups showed that lower percentage of DM2 patients had abnormal results on following tests: Addenbrooke's Cognitive Examination-Revised, Raven Standard Progressive Matrices, Block Design, copy and recall of Rey-Osterieth Complex Figure, number of categories and perseverative responses on Wisconsin Card Sorting Test and Boston Naming Test (p < 0.01), as well as Trail Making Test-B and Spatial Span (p < 0.05). Our results showed significant dysexecutive syndrome and certain impairment of episodic verbal memory in DM2 patients that are reflective of frontal (especially frontostriatal) and temporal lobe dysfunction. On the other hand, dysexecutive and visuospatial/visuoconstructional deficits predominate in DM1 which correspond to the frontal, parietal (and occipital) lobe dysfunction.