(NYT Syndicate) -- A new brain scanning technique developed by doctors in New York can apparently detect signs of Alzheimer's disease years and perhaps decades before it begins destroying memory and mental function, potentially offering hope to millions of Americans who will be afflicted with the disease.

In a study in the current Lancet, an English medical journal, researchers describe how magnetic resonance imaging tests can reveal shrinkage in part of the brain that is a telltale sign of the onset of Alzheimer's well before people notice they are losing memory.

While no cure has been developed for Alzheimer's, which severely afflicts more than 4 million Americans and affects millions more in milder forms, a number of treatments have been shown to help slow its ravages and fend off dementia.

Generally, the disease now is not diagnosed until it has become apparent when people are in their 60s or 70s, and brain scans have not been commonly used as diagnostic tools. If the new brain scan proves economical and workable on a large scale, it could one day allow millions of people to begin treatment to preserve mental function before their Alzheimer's becomes severe, or at least give them the warning they need to be vigilant for any symptoms. Alzheimer's is the fourth leading cause of death in the US.

"This is quite exciting and very significant work," said Dr. Zaven Khachaturian, senior consultant to the Chicago-based Alzheimer's Foundation and a former top federal Alzheimer's researcher.

In the Lancet paper, a team led by Dr. Mony de Leon of New York University's medical school describes how shrinkage of part of the brain called the entorhinal cortex, which is a key memory processing center, is visible in people with very mild forms of Alzheimer's, years before they begin noticing memory loss.

In the last decade, a number of research teams around the US and Europe have made key breakthroughs in correlating physical changes in parts of the brain among people as young as their late 20s to the onset of Alzheimer's.

De Leon's team found that compared to healthy volunteers, as measured by MRI scans, the entorhinal cortex was on average 45 percent smaller among people with severe Alzheimer's and 27 percent smaller among people with milder cases.

De Leon said he and his colleagues believe they have found "a way to measure what may be the earliest changes in the memory-processing areas of the brain" that are a sign of the development of Alzheimer's.

MRI scans may be a considerably faster, less expensive way to diagnose early Alzheimer's than the traditional practice of administering memory and learning tests, taking a family medical history and performing other physical examinations.

Damage to the entorhinal cortex in people with Alzheimer's proved to be greater than damage to another part of the brain called the hippocampus, which has been a focus of considerable research, and it was also a "more reliable disease marker," according to the NYU team.

De Leon's team developed a new way of measuring the size of the entorhinal cortex based on what they call structural landmarks inside the brain.

"This is a preliminary study that should be expanded over a period of years," de Leon said, but added that "for people with a family history of Alzheimer's, it may be possible to observe such changes and to treat the brain years before there are any signs of memory loss."

Dr. Kirk Daffner, co-director of the memory disorder unit at Brigham and Women's Hospital in Boston, said that "at this point, there is no major advantage to knowing many decades in advance" that someone is developing Alzheimer's because there is nothing close to a cure.

However, a drug trade-named Aricept, Ginko herbal extracts and treatments involving vitamin E and estrogen have all shown benefits in controlling symptoms of Alzheimer's, which begin with memory loss and progress to incapacitation.

"Hopefully, in the next 5 to 10 years there will be the increasing possibility of medications that improve cognition or slow down the disease's progression," Daffner said.

Khachaturian said work by de Leon and others is bolstering the case that Alzheimer's "should no longer be thought of as a disease of the aged. It's more a disease of the young" that takes decades to become apparent to its victims, Khachaturian said.

Copyright 1999 The New York Times Syndicate. All rights reserved.

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