Brain imaging to diagnose Alzheimers
Adam Fleisher, MD, is a neurologist, dementia specialist at Banner Alzheimer’s Institute. His office can be reached at (602) 839-6900.
Question: I’ve heard about using brain imaging to diagnose Alzheimer’s disease. Who can be diagnosed using brain imaging?
Answer: Guidelines for evaluating patients with memory/thinking problems and diagnosing Alzheimer’s disease and related dementias are established by the American Academy of Neurology and similar organizations. These recommendations include the use of clinical evaluations; memory/thinking tests; lab work to rule out reversible causes of memory problems; and brain imaging to assess brain structure, function and pathology.
When Alzheimer’s/dementia cannot be confidently diagnosed using clinical and cognitive assessments alone, other tests help identify underlying disease biomarkers that may indicate the source of memory and thinking problems. Blood and/or spinal fluid tests along with imaging procedures to assess brain structure, function and pathology can detect abnormalities in the brain associated with Alzheimer’s.
Imaging techniques such as magnetic resonance imaging (MRI) and flurodeoxyglucose positron emission tomography (FDG-PET) can detect both structural and functional abnormalities in the brain that are commonly associated with Alzheimer’s. FDG-PET, which focuses on brain function, is most sensitive to identifying patterns of Alzheimer’s disease in individuals with advanced disease symptoms. It is less sensitive at earlier stages of the disease.
In comparison, newly approved amyloid PET imaging enables clinicians to evaluate the actual pathology of Alzheimer’s in the brain by detecting amyloid, a protein fragment that is a hallmark feature of the disease.
Research suggests that amyloid plaques, which are clusters of amyloid fragments in the brain, begin accumulating as early as 15 to 20 years before clinical symptoms of Alzheimer’s emerge. Therefore, brain imaging to detect amyloid may provide the earliest pathological evidence of Alzheimer’s in patients with dementia and mild cognitive impairment. It also may also serve as a presymptomatic biomarker of Alzheimer’s.
However, since everyone responds differently to toxicity in the body, the mere presence of amyloid does not guarantee that an individual will eventually exhibit the symptoms of Alzheimer’s disease. In fact, approximately 30 percent of people over the age of 65 who are considered cognitively normal have amyloid in their brain; that number increases to 45 percent of cognitively normal people over the age of 80.
Current guidelines limit non-research amyloid imaging in the clinical setting to patients who exhibit symptoms of Alzheimer’s disease as a diagnostic and treatment decision making tool. The Memory Disorders Clinic at Banner Alzheimer’s Institute uses brain imaging, including the new amyloid PET technique, in the clinical management of Alzheimer’s/dementia patients.