Early Cognitive Impairment in Multiple Sclerosis

Cognitive impairment in Multiple Sclerosis (MS) occurs in 50% of patients and has a major social impact. There is no clear correlation between cognitive dysfunction and disease duration and recent studies have pointed out that it may affects patients at the very early stages of the disease especially in tasks involving sustained attention, processing speed, working memory and executive function. Recent imaging and pathology studies have shown that MS affects white matter as well as grey matter. Unlike white matter lesion burden or distribution, grey matter atrophy has often been linked to cognitive impairment. Microscopic injury of Normally Appearing White Matter (NAWM) explored by non conventional MRI sequences has also been shown to be involved in pathophysiology of cognitive disorders. Nevertheless mechanisms of cognitive impairment remain unclear. The relationship between cortical injury and diffuse white matter tracts damage and their respective contribution to cognitive dysfunction affecting patients during the first years of the disease is still under investigation. This study aims at investigating structural and functional correlates of early cognitive impairment using multimodal MRI. Relapsing Remitting MS (RRMS) patients with disease duration of less than 5 years will be included. Patients with and without cognitive impairment will be compared to healthy controls. All subjects will perform a clinical and neuropsychological evaluation before the MRI examination. We will combine new available MRI techniques using a 3 Tesla magnet in order to evaluate precisely cortical and white matter tracts lesions in patients with cognitive MS. These techniques will include : * 3D T1 sequences to study cortical atrophy using VBM. * Diffusion tensor imaging fibre tracking to study selected white matter tracts that may be involved in cognitive disorders, such as the thalamus-cortical or the striatum-cortical tracts connecting sub-cortical structures to the prefrontal cortex. * Functional MRI sequences during a working memory task and during the resting state in order to describe functional networks and their possible reorganization in patients with or without cognitive impairment.