Alzheimer's Grips Brain Before Mental Decline
Biomarkers, Brain Scans Identify Healthy People at High Risk of Dementia
Dec. 14, 2009 - Apparently healthy people with no sign of mental decline may
already have significant Alzheimer's disease, new studies show.
This "preclinical Alzheimer's disease" puts a person at high risk of an
eventual diagnosis of Alzheimer's disease, find studies led by John C. Morris,
MD, director of the Alzheimer's Disease Research Center at Washington
University, St. Louis.
Morris and colleagues studied 135 people at ages ranging from 65 to 88. They
were "sharp as a tack" on sophisticated tests of mental function, Morris
But brain scans showed that more than 22% already had the telltale plaque
deposits in their brains that characterize Alzheimer's disease.
A second study of 159 people at an average age of 71 showed that those with
this "preclinical Alzheimer's disease" were nearly five times more likely to
develop very mild Alzheimer's-type dementia.
"Now we have a revolutionary change in Alzheimer's disease," Morris tells
WebMD. "This is the first evidence that people who were perfectly healthy had
amyloid plaques, and that these individuals are at very high risk of symptoms
of Alzheimer's disease over a three- to four-year period."
These are major findings, agrees Gary Kennedy, MD, director of geriatric
psychiatry at Montefiore Medical Center in New York. Kennedy was not involved
in the Morris study.
"The reason this is important is we would like to identify people with this
illness before they get disabled," Kennedy tells WebMD. "If we had agents that
really slowed down the progression of Alzheimer's disease, we could forestall
disability to end of a person's lifetime, and the burden of Alzheimer's disease
on society would level off."
That day remains far off. The bad news from the Morris studies is that by
the time people show clinical signs of Alzheimer's disease -- currently the
only way this fatal illness is diagnosed -- it may be too late. Such symptoms
now appear to be the result of irreversible brain damage.
"Even if we knew you had preclinical Alzheimer's disease in your brain and
ergo high risk of symptoms in a few years, we can't do anything about it now,"
Morris says. "So I really think we have to follow a dual course. We have to
clarify, refine, and define our clinical detection of Alzheimer's disease --
but at the same time we have to develop treatments for prevention. Because we
would like to couple knowing your risk with reducing your risk."
While the brain scans were able to detect the buildup of amyloid plaque in
the brain, a different test -- one that checks for Alzheimer's biomarkers in
cerebrospinal fluid -- may detect Alzheimer's risk even earlier.
Morris and colleagues studied one patient who eventually died with
Alzheimer's disease. He was positive for the biomarker but his brain scan did
not detect signs of Alzheimer's.