[Biomarkers of Alzheimer's disease in older and oldest old patients].

Alzheimer's disease (AD) is the most common neurodegenerative disorder in older patients, leading to progressive cognitive impairment. Brain amyloid and tau deposits are the main pathological features of the disease and may appear several decades before the onset of clinical symptoms. The biomarkers of AD, measured in the plasma or in the cerebrospinal fluid, reflect the brain accumulation of beta-amyloid and tau. Therefore, they enable early and more accurate etiological diagnosis when combined with brain neuroimaging and neuropsychological assessment. The new definition of AD brings biomarkers forward, shifting the focus from symptoms to brain changes in living patients. The growing body of evidence from longitudinal studies has established their ability to improve the accuracy of AD diagnosis but also to predict the progression of cognitive impairment. The biomarkers of AD are also important for recruiting participants who are at increased risk of developing AD dementia in drug trials. Beyond their role in clinical research, these tools have been increasingly used for several years in clinical practice in secondary and tertiary-referral memory clinics. However, interpreting the results of AD biomarkers may be delicate in the oldest old patients with comorbidity. A tailored, patient-centered decision is mandatory in these situations. Complicated ethical issues may also arise in using these biomarkers in asymptomatic subjects. In the absence of clear guidelines for their utilization, we hereby discuss their potential interests and limitations in older adults.