For the first time in 27 years, researchers have released new criteria for diagnosing Alzheimer's disease. With tests to pick up the earliest stages of the disease not yet ready for widespread use, the new guidelines will have little immediate impact on patients, but they are intended to provide a framework for research and to hopefully prepare clinicians for the day when effective treatments become available.
The guidelines, released today by the Alzheimer’s Association and the National Institute on Aging (NIA) and published online in Alzheimer’s & Dementia, reflect the growing understanding that the neurological damage of Alzheimer's begins years, even decades, before symptoms appear and that future treatments will probably work best when started as early as possible. They expand the definition of Alzheimer's to include two new stages that precede full-blown dementia: a presymptomatic phase and a phase marked by mild cognitive impairment.
The new guidelines are the revised version of recommendations made last year.
At a press conference yesterday, NIA's Creighton Phelps explained that one of the main revisions was to clarify which recommendations pertain to researchers and which pertain to clinicians. In particular, the working groups of experts who drafted the guidelines say that Alzheimer's biomarker tests, which pick up early biological signs of the disease, are not yet ready for widespread clinical use. (Because the newly proposed presymptomatic phase of the disease can be detected only with biomarker tests, that designation is only for use by researchers at this time.)
In recent years, researchers have made considerable progress on biomarkers, including scans that detect changes in brain anatomy and physiology and tests that measure levels of β-amyloid—a peptide thought to be an important player in the disease—in the brain and cerebrospinal fluid. These tests can pick up signs of Alzheimer's disease in people before memory problems appear, and they are already being used in clinical trials. Many researchers think the reason so many clinical trials for prospective Alzheimer's treatments have failed in recent years is that the patients enrolled in the trials were too far along in the course of the disease. Biomarkers that can pick up early signs of the disease might enable doctors to start treatment before too much irreversible damage to the brain has occurred. For now, that's done only in clinical trials.
The working groups concluded that although biomarkers are invaluable for research, more work is needed before they can be more widely used by doctors. For example, the methods must be standardized to ensure they're used consistently from one hospital to another, and researchers need to come to a consensus on what values demarcate the border between health and disease.