PET Scans May Aid In The Diagnosis Of Alzheimer’s Dementia

by Dr Sam Girgis on July 15, 2011

Alzheimer’s dementia is the most common form of dementia.  The diagnosis can be elusive because the symptoms are very subtle initially but can progress rapidly.  The disease is diagnosed based upon clinical information such as history provided by the patient, history provided by the family, clinical observations, and the presence of neurological and neuropsychiatric features and characteristics.  Physicians can test memory and intellectual function to further help in the identification of the disease.  Several medical organizations have created diagnostic criteria to help in the process of identifying patients with the disease.  In addition, CAT scans and MRI imaging can be used to exclude other brain disorders or subtypes of dementia.  Despite these diagnostic tools, we do not currently have a definitive diagnostic test for the disorder.  Recently, positron emission tomography (PET) neuroimaging using a tracer compound called florbetapir-fluorine-18 (florbetapir) has shown some usefulness in the diagnosis of Alzheimer’s dementia.  Florbetapir binds to beta-amyloid, which has been a characteristic hallmark of Alzheimer’s dementia.  Beta-amyloid plaques form dense and insoluble deposits around the neurons in the brain and have been implicated in the etiology of the disease.  Researchers lead by Dr. Adam Fleisher, from the Banner Alzheimer’s Institute in Phoenix, Arizona, have shown that florbetapir PET imaging can help in the diagnosis of Alzheimer’s dementia.  The results of their study were published online in the recent issue of Archives of Neurology.  The researchers evaluated 68 participants with probable Alzheimer’s dementia, 60 participants with mild cognitive impairment, and 82 older healthy controls with florbetapir PET imaging.  Cerebral to whole cerebellar florbetapir standard uptake value ratios (SUVRs) were computed using the PET imaging data.  The investigators established threshold values for the SUVRs based upon antemortem PET and postmortem neuropathology data from 19 patients with known Alzheimer’s disease.  The participants with probable Alzheimer’s dementia, mild cognitive impairment, and older healthy controls showed statistically significant differences in the uptake of florbetapir based upon the PET imaging studies.  The authors wrote, “The findings of our analysis confirm the ability of florbetapir-PET SUVRs to characterize amyloid levels in clinically probable [Alzheimer’s dementia], mild cognitive impairment, and older healthy control groups… It introduces criteria to determine whether an image is associated with an intermediate-to-high likelihood of pathologic [Alzheimer’s dementia] or with having any identifiable cortical amyloid level above that seen in low-risk young controls”.  This study is remarkable because it adds to the evidence that florbetapir PET scan imaging can be used to accurately help in the diagnosis of Alzheimer’s dementia.  Since we don’t have a definitive diagnostic test for the disorder, adding the use of florbetapir PET imaging will hopefully help in the diagnostic process and lead to earlier treatment.

Reference:

Adam S. Fleicher et al. “Using Positron Emission Tomography and Florbetapir F 18 to Image Cortical Amyloid in Patients With Mild Cognitive Impairment or Dementia Due to Alzheimer DiseaseArch Neurol published online July 11, 2011 doi:10.1001/archneurol.2011.150

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