ORLANDO, Fla. – Mild cognitive impairment, a subtle memory disorder that affects millions of older Americans, actually may be early Alzheimer’s disease or another early form of dementia known as cerebral vascular disease, according to a new study.
If that conclusion is correct, it could mean up to three times as many people have the early stages of brain lesions that are found in people with Alzheimer’s or other dementia, doctors said.
It is estimated that 4.5 million Americans have Alzheimer’s, the most common form of dementia.
As many as an additional 9 million people might have mild cognitive impairment, a condition involving short-term memory loss without dementia symptoms such as impaired judgment or reasoning.
“If you do the math, the numbers become astronomical,” said Piero Antuono, an Alzheimer’s specialist and professor of neurology at the Medical College of Wisconsin. “It implies a much bigger phenomenon than we originally thought.”
The new research is part of a continuing Religious Orders Study of 1,000 Catholic priests, nuns and brothers who agreed to undergo annual cognitive testing and donate their brains at the time of their death.
For the new study, which appears in the journal Neurology, autopsies were done on the brains of 180 people in the study, including 37 who had mild cognitive impairment, 60 who were not cognitively impaired and the rest with dementia.
Among the 37 people with mild cognitive impairment, only nine had no signs of Alzheimer’s disease pathology or strokes that had caused areas of dead brain cells.
David Bennett, the study’s lead author, said for years mild cognitive impairment has been thought of as a risk factor for Alzheimer’s but that it did not necessarily mean a person had Alzheimer’s.
But the new study implies that “it’s really the beginning of the disease,” said Bennett, director of the Rush Alzheimer’s Disease Center at Rush University Medical Center in Chicago.
“It’s been hard to prove it because it’s been hard to get the brains of people (with mild cognitive impairment).”
Bennett said the study also helps debunk a belief about how the brain ages.
“There’s a long history of thinking that it’s normal to lose cognition (memory) with age,” he said. “That’s not true. If you are losing cognition at any age, it should be investigated.”
The implications of the study are caught up in a burgeoning understanding of brain disorders such as mild cognitive impairment and Alzheimer’s.
Precise estimates on the number of people with mild cognitive impairment are difficult to find. Many researchers now say that 15 percent to 20 percent of people age 65 and older have the condition, compared with about 10 percent who have full-blown Alzheimer’s.
Some researchers have argued that mild cognitive impairment is really a transitional phase between normal aging and Alzheimer’s.
“What this paper does is give some neuropathological credence to that,” said Ronald Petersen, a spokesman for the Alzheimer’s Association and director of Mayo Clinic’s Alzheimer’s Disease Research Center Rochester, Minn.
Beyond that, he said, the study warns of a looming societal concern now that baby boomers are headed into their 60s.
If mild cognitive impairment is an early warning sign of Alzheimer’s disease, “we’ve got a problem,” Petersen said.
Another surprising finding from the study involved the 60 people who showed no signs of Alzheimer’s or mild cognitive impairment. They had an average age of 85.
After doing autopsies on their brains, half were found to have to significant Alzheimer’s disease pathology and nearly 25 percent had cerebral vascular disease.
Alzheimer’s pathology refers to the accumulation of plaques of amyloid-beta protein around brain cells and tangles of tau protein inside brain cells.
How is it that the disease could be present, but mental ability was not impaired?
Researchers say patients may have been able to avoid mental decline by having so-called brain reserve capacity, a type of structural integrity in the brain that allows people to tolerate the changes brought on by the disease.
“It tells us there’s some good news,” Antuono said. “There may be a way … to lessen the effects of these lesions in the brain.”
Antuono noted that other studies suggest that eating a diet rich in antioxidants, exercising, controlling weight and taking other lifestyle measures that also are good for the heart may increase brain reserve capacity.
Other research suggests that higher levels of education may increase a person’s brain reserve and help ward off Alzheimer’s.
In addition, several drug companies now are conducting trials or planning trials to test various drugs on people with mild cognitive impairment to see if the transition to Alzheimer’s can be halted or delayed, said Neil Buckholtz, chief of the dementias of aging branch of the National Institute on Aging, part of the National Institutes of Health.
“Even people with mild cognitive impairment, not everybody progresses to Alzheimer’s disease,” he said. “Some people, not a lot, seem to remain stable for a long time.”
The National Institute on Aging funded the study.
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