MRI Hippocampal Microstructure and Episodic Memory in Early Multiple Sclerosis

Cognitive deficiencies could occur after a first clinical event of the central nervous system suggestive of MS called clinically isolated syndrome (CIS). Cognitive impairment concerned several cognitive domains including episodic memory, attention, working memory and executive functions. It is recognized the negative impact of cognitive impairment on quality of life and vocational status in patients living with MS. Slowness of information processing speed is the main cognitive dysfunction observed in MS seen at the earliest stage of the disease. Recently an international group of MS experts has explain IPS and episodic memory as the minimal cognitive assessment in patients with MS. Visuospatial and verbal episodic memory deficits have been observed in 18 to 28% of patients assessed after a CIS. Memory disorders could be preceded by microstructural abnormalities without visible atrophy in hippocampus. A recent MRI imaging of diffusion called NODDI (Neurite Orientation Dispersion and Density Imaging) can measure specifically microstructural abnormalities and map the axons in white matter and dendrite in the gray matter. No study has used the NODDI in CIS patients and very few studies have been conducted in MS. The hypothesis is that the dentate gyrus is the anatomical substrate of early episodic memory dysfunction in patients included after a CIS. The identification of predictive MRI biomarker of memory impairment would be a useful and clinically relevant prognostic marker at the early stage of MS. This biomarker could contribute to determine the prognosis of the disease and could help for the monitoring of the patients in clinical practice and clinical trials.