Mild cognitive impairment is already seen by doctors as the first hint of a future Alzheimer's diagnosis in many cases. And the new definition will blur those lines even more, the new report concludes -- begging the question of whether it should be its own diagnosis at all.

"There's been a lot of controversy... about the whole classification called mild cognitive impairment," said Dr. Peter Whitehouse, a geriatric neurologist at the Case Western Reserve University School of Medicine in Cleveland, who wasn't involved in the study.

"The major issue since the beginning (has been) defining its boundaries. Inventing a label like this," he told Reuters Health, "creates confusion."

Mild cognitive impairment was originally diagnosed in people with memory problems but no other difficulties in thinking and reasoning abilities or in completing daily activities.

But that definition has morphed over time to include more people, and in recent recommendations made for the National Institute on Aging and the Alzheimer's Association, now covers people with some trouble doing household chores and hobbies, according to Dr. John Morris, from Washington University in St. Louis.

Those functional problems have traditionally been part of an early Alzheimer's diagnosis.

Morris, the new study's sole author, said he thinks there's so much confusion because most cases of mild cognitive impairment really are the first signs of Alzheimer's.

Other cognitive problems could be due to a stroke, certain medications or thyroid problems, he said -- things that doctors could find explanations for if they kept looking and don't require a separate diagnosis or label, he said.

Morris examined data on more than 17,000 people evaluated for Alzheimer's disease at 33 different centers between 2005 and 2011, including about 6,000 who were originally diagnosed with full-on Alzheimer's or mild dementia related to Alzheimer's.

Those people were 75 years old when they were tested, on average, according to the report published in Archives of Neurology.

Morris determined that based on the new definition of mild cognitive impairment -- including the criterion that someone can have some difficulty with everyday activities -- almost every person with "very mild" Alzheimer's disease dementia could be diagnosed with mild cognitive impairment instead.

That was also the case for more than 90 percent of people with "mild" Alzheimer's disease.

The overlap could lead to a lot of subjective decisions on the part of doctors, according to Morris, when it comes to who has early Alzheimer's and who has mild cognitive impairment -- or to avoiding an Alzheimer's diagnosis because it's seen as "stigmatizing," Morris told Reuters Health.

But that's not usually a good thing for patients and their families, he added.

"If we think the cause of the cognitive impairment is underlying Alzheimer's, by providing the diagnosis to the best of our accuracy, it does allow the patient and the family to start dealing with the reality of the disease at a stage when the patient still has plenty of cognitive ability to participate in those decisions," Morris said.

According to the Alzheimer's Association, 5.4 million people in the United States have the disease, including one in eight aged 65 and older.

Creighton Phelps, head of the Alzheimer's Disease Centers Program at the National Institute on Aging, said that to a certain extent, the line between mild cognitive impairment and early Alzheimer's is indeed "fuzzy" and depends on a doctor's individual judgment. But he added that many researchers still think there's a point in between normal thinking and functioning and Alzheimer's dementia that deserves its own category.

"What other experts say is, you should not be calling it dementia too early, until you're absolutely sure about it," Phelps told Reuters Health.

"In (mild cognitive impairment), you pick up some very early changes. They don't have to quit their job, it's not interfering with their life, but it's measureable," he said. "It's not enough to move them into the dementia category."

Whitehouse said that all of the divisions between normal and mild cognitive impairment and Alzheimer's miss the most important point: that everyone, as they age, should be taking steps to maintain their brain health. That includes keeping your mind and body active, eating a healthy, Mediterranean-style diet and keeping engaged socially, he added.

SOURCE: bit.ly/xHTMf8 Archives of Neurology, online February 6, 2012.

(This story was corrected to change the journal name in paragraph 11, the source line and study link)

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