In the study, published this week in the Journal of the American Medical Association, researchers conducted positron emission tomography (PET) scans of 29 people—15 diagnosed as having Alzheimer’s—living in hospices. Participants agreed to undergo brain autopsies after death. The researchers found that amyloid levels detected during PET imaging correlated closely with levels determined in the autopsy. PET scans of 74 healthy younger people, who were unlikely to have amyloid in their brains, confirmed that the tracer did not detect the protein when there was none.
Despite the successful results, researchers say the clinical impact of the technology is less clear. For one, no disease-modifying treatments are currently available for Alzheimer’s. “We don’t want to spend billions of dollars diagnosing Alzheimer’s when we cannot do anything about it,” says Michael Weiner, professor of medicine, radiology, and psychiatry at the University of California, San Francisco. Weiner was not involved in the study. “But when there are symptoms, patients and families want to know what’s causing it.”
Aisen says he is concerned that the technology could be overused. “Virtually everyone over the age of 40 is worried about memory, and it’s not easy to distinguish the normal memory decline of aging from early Alzheimer’s,” he says.
While preliminary research suggests that people with very mild memory problems who also have amyloid in the brain are more likely to develop full-blown Alzheimer’s, it’s still unclear what the presence of amyloid in healthy people means, or how doctors should use this information. Scientists are using Avid’s tracer and similar amyloid imaging tools to examine this question.
“Physicians and patients and families may interpret a positive amyloid scan as meaning someone has Alzheimer’s,” says Aisen. “When in fact, even if it turns out that amyloid in the brain is the earliest stage of the disease, it may be more than a decade between deposition of amyloid and clinical manifestation of the disease.”
Both Aisen and Morris say the best clinical use might be to rule out Alzheimer’s in the absence of amyloid buildup. Age-related dementia can have a number of causes—some of them treatable—and about 15 to 20 percent of people diagnosed with Alzheimer’s are found on autopsy not to have the disease.
The National Institute on Aging and the Alzheimer’s Association are working on new guidelines for diagnosing the disease. These guidelines will incorporate amyloid imaging and other techniques, such as detection of amyloid in cerebrospinal fluid.