Three million Americans living with mild cognitive impairment should be diagnosed with Alzheimer's disease, a tweak in terminology that could shed light on the condition's cause and prepare patients for an inevitable decline, according to a new report.
The criteria for diagnosing Alzheimer's disease were revised last year, placing more people in a category called mild cognitive impairment, or MCI, which is often a precursor to Alzheimer's.
The new criteria detail three stages of Alzheimer's disease: preclinical (before outward symptoms are visible); mild cognitive impairment (mild memory and thinking changes enough to be noticed but not debilitating); and dementia, or full-on Alzheimer's disease.
But doctors should call the second stage, MCI, what it really is, early symptomatic Alzheimer's disease, said Dr. John Morris, a neurologist and head of the Alzheimer's Disease Center at Washington University School of Medicine in St. Louis.
The revised criteria "now obscure this distinction," said Morris, the author of a report published online first by Archives of Neurology, a peer-reviewed journal published by the American Medical Association.
Morris said that 99.8 percent of people diagnosed with "very mild" Alzheimer's disease dementia and 92.7 percent of those with mild cases could be reclassified.
The update stemmed from mounting evidence that the degeneration of nerves deep within the brain starts years or even decades before memory loss and other cognitive changes are noticeable.
But Morris said that eliminating the boundary between MCI and AD dementia gives doctors "considerable latitude" in determining functional independence as a criteria for diagnosis.
That, he said, results in "nonstandard and ultimately arbitrary diagnostic approaches."
"This recalibration of MCI moves its focus away from the earliest stages of cognitive decline, confounds clinical trials of individuals with MCI where progression to AD dementia is an outcome, and complicates diagnostic decisions and research comparisons with legacy data."
The difference between MCI and early Alzheimer's disease previously has been based on how the symptoms disrupt a person's daily life.
Mild problems might include difficulty shopping, paying bills and cooking as criteria for diagnosis. A problem performing these activities would not yet place a person in the "demented" category, although it would indicate a high likelihood of developing full-blown Alzheimer's.
Morris reviewed the functional ratings of 17,535 patients enrolled at the federally funded Alzheimer's Disease Centers, along with clinical and cognitive data from the National Alzheimer's Coordinating Center.
What he found was that under the new criteria, as many as 99.8 percent of patients would be reclassified as having MCI, denying them the opportunity to face the disease head on and be eligible for clinical research and treatments.
An unintended consequence of the revision is that it has caused more confusion among patients.
For those who are in the earliest stages of the disease, the term MCI should be avoided altogether for those who clearly have early Alzheimer's disease, Morris said.
The overlap of symptoms suggests that distinctions are "artificial and arbitrary," he said, adding that doctors are already treating both conditions as Alzheimer's disease.
Many doctors, he said, are hesitant to tell their patients they have Alzheimer's, preferring an MCI diagnosis, because it is not perceived as a death sentence.
But, Morris said, "If you ask a patient's family if they want to learn what [their disease] is, they overwhelmingly say, 'Yes.'"
This more direct approach of addressing the disease early on would improve families' and patients' ability to plan for the coming decline in memory, by making wills and choosing caregivers.
Diagnosing more people with Alzheimer's disease could increase the number of Alzheimer's diagnoses to 8 million nationwide, Morris said, "and that would underscore the impact in our society."
Alzheimer's is the most common form of dementia, affecting 5.4 million Americans and accounting for 50 to 80 percent of all cases, according to the Alzheimer's Association.
Although the majority of people with the disease are older than 65, and the average age of onset is about 75, up to 5 percent of patients have an early-onset form of the disease, according to the association.
The disease is not a normal part of aging, and it is not the only cause of memory loss. Alzheimer's is progressive and there is no known cure.
Morris advocates an emphasis on the underlying cause of the disease.
But Dr. William Thies, chief medical and scientific officer of the Alzheimer's Association, emphasizes that AD is a continuum and there are differences at the extremes.
The categorization of the continuum is "artificial," and researchers are making their "best guess" about where the worst case of mild cognitive impairment ends and the earliest onset of Alzheimer's begins.
The disease "starts long before we see symptoms outwardly," he said. The span between MCI and AD is "hugely different."
"The person lives by himself and manages his affairs, even if he's a little forgetful," Thies said. "In late state AD, the patient is incapable of doing anything for himself and needs help doing the most basic activities."
Researchers want to know where the dividing line is and to be able to support that knowledge with data. "Not all studies reflect the same answers," he said. "We need a number of studies not to tell us where the line needs to be and how wide the line. It's not a white line; it's fuzzy."
"We are trying to quantify where the line is between MCI and early dementia and where the line lies," Theis said. "It will take community-based population studies that need to be done."
The new criteria, published in 2011 in "Alzheimer's & Dementia: The Journal of the Alzheimer's Association" followed a report that brain areas affected by Alzheimer's disease start shrinking up to a decade before symptoms appear.