Cholinergic Markers Alzheimer's Disease

Strategy: Within the framework of the usual management, the investigators propose the protocol to patients who had an assay of the CSF biomarkers with a CSF AD biological profile before the introduction of an IChEs and having accepted Their CSF will stocked in our biobank. Patients will only have additional neuropsychological assessments. The rest of the care comes under the current care. The quantification of ACh in the CSF will be performed in tandem mass spectrometry after separation by liquid chromatography (LC-MS / MS). AChE activity will be determined by colorimetric determination. The investigators's objective is to prospectively explore the predicting value of CSF Ach and AchE-a levels on ChEIs response in AD patients. The evaluation criteria will be * Difference of the mean value of the ACh level and AChE activity in the CSF between the responder and non-respondier groups of patients. * "Responder" patients are defined by an improvement of at least 4 points on the ADAS-Cog (cognitive part) ADAS-Cog after 6 months of treatment. * "Non-responders" are defined as aggravation, lack of improvement or improvement \<4 points on the ADAS-Cog scale.