The brain areas affected by Alzheimer's disease start shrinking up to a decade before symptoms like memory loss appear, according to new brain imaging research. The discovery, which adds to growing evidence that Alzheimer's is a slowly emerging disease, could help scientists identify people at risk before the damage is done.
The research team, led by Dr. Bradford Dickerson, associate professor of neurology at Harvard Medical School and director of the Frontotemporal Dementia Unit at Massachusetts General Hospital in Boston, assessed the size of the hippocampus -- the brain's memory center -- and other brain regions affected by Alzheimer's disease. They used magnetic resonance imaging in 65 people who were cognitively normal. Among those with the smallest Alzheimer's-related brain area measurements, 55 percent were later diagnosed with the disease.
"It tells us that areas of the brain that are important for memory and other aspects of thinking are beginning to shrink in people who don't yet have symptoms," said Dickerson, lead author of the study published today in the journal Neurology. "We at least have the potential to detect changes a number of years in advance, and hopefully we could do something about it."
Alzheimer's disease, the most common cause of dementia among older adults, is estimated to affect 5 million Americans and is the fifth leading cause of death in the United States, according to the U.S. Centers for Disease Control and Prevention.
Dickerson compared detecting Alzheimer's-related brain shrinkage to measuring cholesterol levels in someone at risk for heart disease.
"We need to be developing a cholesterol test for Alzheimer's disease, in a sense," he said. "We need to have markers that we can identify in people that are still normal to boost that chance of preventing or slowing the disease."
But a dearth of effective treatments means early detection won't yet save lives.
"This imaging finding will not translate into new treatments. However, it does increase the rationale for utilizing preventive therapies," said Dr. Steven DeKosky, professor of neurology and dean of the University of Virginia School of Medicine.
Brain shrinkage and memory loss are features of normal aging but happen earlier in people with Alzheimer's disease.
Researchers have previously shown that positron emission tomography (PET) scans can detect plaques of amyloid protein in the brain -- the hallmark of Alzheimer's disease -- before clinical symptoms appear. MRI is cheaper and more widely available, but still expensive.
"The cost of volumetric MRI will be greater than the cost of memory testing, which is generally inaccurate, or genetic testing, which also has high error rates. It will also be more expensive than spinal taps, but less invasive," said Dr. Paul Aisen, professor of neurology at the University of California, San Diego and director of the Alzheimer's Disease Cooperative Study. "It will be less expensive than amyloid PET imaging."
Dickerson said the MRI-based tool is currently intended for research only, and is "not the kind of thing people can go and get from their doctor."
The next step, he said, is to replicate the findings in another, bigger group of study participants. He will also compare its usefulness as a biomarker to other experimental screening tools, such as PET scans and spinal taps.
In July 2010, a working group from the National Institute on Aging and the Alzheimer's Association proposed changes to the diagnostic criteria for Alzheimer's disease to include brain imaging and tests on cerebrospinal fluid. The hope is that identifying patients in earlier stages of the neurodegenerative disease may boost treatment effectiveness.
"We don't yet have drugs that can do anything about Alzheimer's disease," Dickerson said, "but maybe we're testing them in people too late in the process."