[Diagnosis of Alzheimer's disease].

Alzheimer's disease is a neurodegenerative disorder leading to cognitive impairment (amnesia, aphasia, apraxia and agnosia). The prevalence of this age related disabling illness is increasing. During the course of the disease, the clinical diagnosis will be that of "possible Alzheimer's disease", then "probable Alzheimer's disease". But the diagnosis of "definite Alzheimer's disease" requires a post-mortem brain examination and the demonstration of numerous senile plaques and neurofibrillary tangles in hippocampal and association cortical areas. The neuropathological examination confirms probable Alzheimer's disease clinical diagnosis in 85% of the cases examined in medical schools. However, with much more than 15% errors, the early diagnosis of Alzheimer's disease must be improved since it is a key factor for the therapeutic approach, and more especially for the efficiency of drug trials. At the present time, there are new leads for a biological diagnosis in the blood or the CSF. However, the natural (and molecular) history of Alzheimer's disease points out that all biochemical dysfunctions remain in the CNS, and more particularly in association brain areas. This is demonstrated using reliable biochemical markers such as A beta and pathological Tau proteins, which are the basic components of amyloid deposits and neurofibrillary tangles, respectively. Also, a genetic diagnosis can be performed in half of familial autosomic dominant Alzheimer's disease, which represents less than 1% of all Alzheimer's disease cases. Together, this shows that there is a lack of reliable Alzheimer's disease markers. The search for new specific markers (clinical, epidemiological, genetic, biochemical, biological) must go on.