Memantine is an NMDA receptor antagonist that improves cognitive and behavioural deficits in patients with Alzheimer disease, vascular dementia and mixed dementia. This study is focused in proving the efficacy of Memantine in ameliorating one of the most frequent symptoms of patients with MS which is attention and memory deficits. Memantine is a safe drug in patients with MS and it has been administered to MS patients with pendular nystagmus (Starck et al J Neurol 1997). The study will have the power to detect differences in such clinical question by studying 60 MS patients with cognitive impairment (n=60)) with a crossover design. Indeed, we plan to use a new and powerful surrogate marker such as attention evoked potentials developed in our center. Finally, because there are evidences that Memantine might improve MS outcome by closing the Brain-Blood barrier (which is the best therapeutic target in this disease) (Paul et al J Pharmacol Exp Ther 2002), an exploratory study of its efficacy in preventing new MRI lesions might also be included in the design.~Aims: To assess the efficacy of Memantine in improving the cognitive impairment in patients with Multiple Sclerosis (MS) Primary end-point: to assess the efficacy of Memantine in improving memory deficit in MS patients using the SRT scale~Secondary end-points:~To assess the efficacy of Memantine in improving the performance in the individual neuropsychological tests for attention (PASAT3, SDMT, Stroop), executive (Raven, MATTIS) and memory (10/36, SRT), in the neuropsychological global scale BRB-N Z (Sepulcre et al, submitted) in quality of life (SF36), disability (EDSS, MSFC, MSSS) and fatigue (Krupp).~to assess the effect of Memantine in attention evoked potentials (EP)~to assess the effect of Memantine in clinical course (new relapses, relapse rate, patients free of relapses), disability (EDSS, MSFC, MSSS) and MRI parameters (active lesions: new T2 lesions, change in T2 lesion load, new gadolinium enhancing lesions and global and regional atrophy) in the response to Memantine. MRI study is optional.~to identify the predictors of good or bad response to Memantine therapy by using EP as surrogate markers.~Design: double blind, randomize and crossover clinical trial with Memantine compared with placebo in MS patients. Because Memantine have a hal-life of 2 to 4 days period, at the end of the 6 month, patients we will stay 3 weeks without any therapy (placebo or Memantine) in order to washout Memantine in the therapeutic group
To assess the efficacy of Memantine in improving the cognitive impairment in patients with Multiple Sclerosis (MS)