For the first time in 27 years, new criteria and guidelines for the diagnosis of Alzheimer's disease have been published by three expert workgroups spearheaded by the Alzheimer's Association and the National Institute on Aging (NIA) of the National Institutes of Health (NIH).

The workgroups published four articles including ready-to-use clinical diagnostic criteria for Alzheimer's disease dementia and mild cognitive impairment (MCI) due to Alzheimer's. A research agenda was proposed for preclinical Alzheimer's. The use of biomarkers in Alzheimer's dementia and MCI due to Alzheimer's was also proposed as a research agenda only, and is not intended for application in clinical settings at this time.

The articles — collectively, the National Institute on Aging/Alzheimer's Association Diagnostic Guidelines for Alzheimer's Disease — expand the definition of Alzheimer's to include two new phases of the disease:

1. Presymptomatic; and
2. Mildly symptomatic but pre-dementia, along with;
3. Dementia caused by Alzheimer's.

This reflects current thinking that Alzheimer's begins creating distinct and measurable changes in the brains of affected people years, perhaps decades, before memory and thinking symptoms are noticeable.

"It is our hope that incorporating scientific knowledge gained and technological advances made over the past quarter century will improve current diagnosis, bring the field closer to earlier detection and treatment, and ultimately lead to effective disease-modifying therapies," said William Thies, PhD, chief medical and scientific officer at the Alzheimer's Association. "Development and publication of these articles is a major landmark in the field. That said, publication of these articles is not yet the end of the process of developing new diagnostic criteria for Alzheimer's, but is another major step in the process."

"The new guidelines reflect today's understanding of how key changes in the brain lead to Alzheimer's disease pathology and how they relate to the clinical signs of mild cognitive impairment and Alzheimer's disease dementia," said Creighton Phelps, PhD, program director of the Alzheimer's Disease Centers Program at the National Institutes of Health. "We are also beginning to be able to detect these changes at a preclinical stage, long before symptoms appear in many people. With further research on biomarkers, as set forth in the new guidelines, we may ultimately be able to predict who is at risk for development of mild cognitive impairment and Alzheimer's dementia, and who would benefit most as interventions are developed."

The proposed new Alzheimer's disease diagnostic guidelines were published online today by Alzheimer's & Dementia: The Journal of the Alzheimer's Association. Hard copy publication is scheduled for the May 2011 issue of the journal.

Three stages of Alzheimer's Disease

The current diagnostic criteria for Alzheimer's*, for the most part, focus on reliable diagnosis when signs of problems in thinking, learning, and memory are noticeable to an individual, family, and friends. But research tells us that Alzheimer's likely begins years, maybe even decades, prior to symptoms appearing.

The new articles refer to three phases of Alzheimer's disease progression over time:

• Preclinical Alzheimer's disease: Measurable changes in biomarkers (such as brain imaging and spinal fluid chemistry) that indicate the very earliest signs of disease, before outward symptoms are visible. Currently, there are no clinical diagnostic criteria for this phase, but the group provides a scientific framework to help researchers better define this stage of Alzheimer's. (See supplement 5.)
• Mild cognitive impairment (MCI) due to Alzheimer's disease: Mild changes in memory and thinking abilities, enough to be noticed and measured, but not impairment that compromises everyday activities and functioning.
• Dementia due to Alzheimer's disease: Memory, thinking and behavioral symptoms that impair a person's ability to function in daily life.

According to the authors, in order to facilitate the possibility of future presymptomatic treatment of Alzheimer's, it was important to define the disease from the earliest changes in the brain, not only the observable, symptomatic stages of the disease.

The authors propose that Alzheimer's begins with a long asymptomatic period during which detrimental changes are progressing in the brain, and individuals with biomarker evidence of these changes are at increased risk for developing cognitive and behavioral impairment and progression to Alzheimer's dementia.

A biomarker is a naturally occurring, measurable substance or condition in the body that reliably indicates the presence or absence of disease or the risk of later developing a disease; for example, blood glucose levels are a biomarker of diabetes, and cholesterol levels are a biomarker of cardiovascular disease risk. Both fluid and imaging measures are being tested as possible biomarkers for Alzheimer's.

There was a broad consensus within the workgroups that much additional research needs to be done to validate the application of biomarkers as they are proposed in the newly-published articles. According to the authors, "The definitive studies … are likely to take more than a decade to fully accomplish. Thus, we must move quickly … and adjust our models and study designs as new data become available."

"If we can definitively determine the risk of developing Alzheimer's dementia in people who have biomarker evidence of brain changes but are not showing outward symptoms, we will open an important window of opportunity to intervene with disease-modifying therapies, once they are developed," Thies said.

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