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)."