Diagnostic tests for Alzheimer disease

Abstract

![Graphic][1]</img> Imaging with [18F]fluorodeoxyglucose-positron emission tomography (FDG-PET) offers excellent insights into regional brain dysfunction but fails to deliver tangible benefits in most clinical settings in persons with suspected cognitive impairment. The radiation exposure from a single FDG-PET brain scan is 1.3 rem, equivalent to about 3 chest X-rays or 4 months of background radiation; therefore, while unnecessary exposure to radiation is to be avoided, my view is not driven by risks of PET scanning. It is the realities of clinical diagnostics and the lack of potent interventions for specific dementing illnesses that limit the value of FDG-PET. Diagnoses of mild cognitive impairment (MCI) or dementia are entirely based on information obtained from the history and cognitive examination. Distinguishing abnormal cognition from normal cognition can sometimes be very challenging. As clinicians, we are often confronted with patients who report cognitive complaints that seem discordant with their level of daily functioning. Because there is a wide range of what is considered normal based on education, occupation, and cultural background, and because mood or motivation issues sometimes cloud performance, the distinction between normal and impaired can be very difficult. An FDG-PET scan will not solve this problem. The availability of FDG-PET offers a seductive but flawed logic that goes something like this: “Even though I don't know clinically whether the person has cognitive impairment or not, an abnormal FDG-PET would confirm that the cognitive complaints … [1]: /embed/inline-graphic-1.gif