Alzheimer's disease normally gets a definitive diagnosis only after the patient dies, and an autopsy finds certain distinctive structures in the brain.
Recently, though, scientists have been seeking some sort of biomarker - a characteristic that can be identified while the patient is still alive.
Emerging research on Alzheimer's suggests that the underlying physical disease begins years - maybe decades - before any symptoms appear. Kejal Kantarci studies Alzheimer's at the Mayo Clinic in Rochester, Minnesota.
"We wanted to investigate whether people who have normal cognitive function, but in their 70s and 80s, have any signs of Alzheimer's or other dementia-related pathology through imaging," she says.
In a new study, Kantarci and her colleagues put more than 300 older adults through some advanced imaging procedures.
The participants had positron emission tomography, or PET scans to identify the level of amyloid-beta in the brain that may signal Alzheimer's. About one-third of them had significant amyloid-beta deposits.
They also got a special kind of MRI scan to look for a biomarker that may indicate Alzheimer's. And those with significant amyloid-beta deposits tended to have high levels of the choline/creatine biomarker. They also scored lower on cognitive tests.
"We found that there is a relationship between the biochemical changes in the brain that we measured and the cognitive performance in the individuals," Kantarci says.
The MR spectroscopy, which is the MRI-type scan, identified people who scored lower on various tests of cognitive function, and who may be at risk for developing Alzheimer's.
The researchers caution that MR spectroscopy can not be used to diagnose Alzheimer's. But this work and other research suggests that it may soon be possible to identify people at higher risk of Alzheimer's and other forms of dementia before they show any symptoms.
Kantarci admits that's not going to help patients now, because there are no effective treatments. "But when they come about," she says, "there will be a chance for us to identify those normally functioning individuals who will benefit most from preventive treatment."
In addition, researchers trying to develop treatments may be able to use this biomarker in tests to assess how effective a new drug is.