May 24, 2011
Scientists are moving closer to diagnosing Alzheimer’s disease at an earlier stage using special brain scans. The scans, which are not routinely available in doctors’ offices, should make it easier to know for sure whether someone has Alzheimer’s earlier in its course, when treatments may be more effective and patients can better plan for the future. Currently, the only way to get a definitive diagnosis is to examine the brain after death during an autopsy.
The imaging technique picks up the presence in the brain of plaques, which are made up of clumps of beta-amyloid protein fragments. Plaques are a telltale sign that someone has Alzheimer’s, though their role in the disease is not well understood. Someone may have dementia, but if they do not have plaques, their dementia is due to a condition other than Alzheimer’s.
Between 10 and 20 percent of people who are given a diagnosis of Alzheimer’s turn out not to have the disease when their brains are examined at autopsy. And doctors miss the diagnosis of Alzheimer’s in about a third of patients with early disease and only mild memory loss and other symptoms. Someone who comes to the doctor’s office complaining of depression, for example, may actually be in the early stages of Alzheimer’s.
The imaging techniques involve the use of positron emission tomographic, or PET, scans. They use various dyes that latch on to particles of beta-amyloid in the brain, making it possible to see plaques on the brain scans in living people.
Most recently, an advisory panel to the US Food and Drug Administration recommended approval of an imaging technique developed by Avid Radiopharmaceuticals, pending further study of the technique. The company has developed a brain dye called florbetapir F 18 that attaches to beta-amyloid, which then lights up on PET scans.
In a recent study, florbetapir-PET imaging was performed on the brains of 35 men and women who were in hospice or long-term care facilities and nearing the end of their lives, about half of whom were thought to have Alzheimer’s. Their brains were then examined after they died, to see if the PET scans in the living people were consistent with the findings on autopsy.
In almost all the cases, the living brain scans matched the autopsy findings. One patient who was thought to have Alzheimer’s actually had dementia of other causes. Two others turned out to have Alzheimer’s, though they were given other diagnoses while alive.
Similar scans were performed on 74 young and healthy individuals under age 50. Presumably, their brains would be relatively free of plaque, which turned out to be the case. The study appeared in the Journal of the American Medical Association.
The findings give new weight that such scanning techniques will prove effective in diagnosing Alzheimer’s definitively at earlier stages. Scientists need to do further study to determine how much plaque defines a diagnosis, and doctors need to be trained in carrying out and interpreting test results.
The technique is also being used to assess the effects of various Alzheimer’s drugs in development. By monitoring brain plaques, researchers can determine whether an experimental drug is working by preventing the buildup of beta-amyloid in the brain. Current medications for Alzheimer’s may ease symptoms for a time but do not stop the downward progression of disease.
Additional work needs to be done to evaluate the accuracy of the technique. And doing PET scans with brain dyes is an expensive procedure that cannot be routinely performed in a doctor’s office. Still, the findings add another piece of the puzzle to diagnosing Alzheimer’s disease at earlier stages, potentially allowing patients, family members and doctors to plan for the future more effectively.
Christopher M. Clark, MD; Julie A. Schneider, MD; Barry J. Bedell, MD, PhD; et al: “Use of Florbetapir-PET for Imaging Beta-Amyloid Pathology.” Journal of the American Medical Association, Vol. 305 (No. 3), January 19, 2011, pages 275-283.