"Government and other scientists are proposing a new way to define Alzheimers disease basing it on biological signs such as brain changes rather than memory loss and other symptoms of dementia that are used today. The move is aimed at improving research by using more objective criteria like brain scans to pick patients for studies and enroll them sooner in the course of their illness when treatments may have more chance to help. But its too soon to use these scans and other tests in routine care because they havent been validated for that yet experts stress. For now doctors will still rely on the tools theyve long used to evaluate thinking skills to diagnose most cases. Regardless of what tests are used to make the diagnosis the new definition will have a startling effect Many more people will be considered to have Alzheimers because the biological signs can show up  to  years before symptoms do. The numbers will increase dramatically said Dr. Clifford R. Jack Jr. a Mayo Clinic brain imaging specialist. There are a lot more cognitively normal people who have the pathology in the brain who will now be counted as having Alzheimers disease. He led a panel of experts working with the Alzheimers Association and the National Institute on Aging that updated guidelines on the disease published Tuesday in Alzheimers  Dementia The Journal of the Alzheimers Association.  About Alzheimers About  million people worldwide have dementia and Alzheimers is the most common form. In the U.S. about . million have Alzheimers under its current definition which is based on memory problems and other symptoms. About onethird of people over  who show no thinking problems actually have brain signs that suggest Alzheimers Jack said. There is no cure  current medicines such as Aricept and Namenda just temporarily ease symptoms. Dozens of hopedfor treatments have failed and doctors think one reason may be that the studies enrolled patients after too much brain damage had already occurred. By the time that you have the diagnosis of the disease its very late said Dr. Eliezer Masliah neuroscience chief at the Institute on Aging. What weve realized is that you have to go earlier and earlier and earlier just as doctors found with treating cancer he said. Another problem as many as  percent of people enrolled in Alzheimers studies based on symptoms didnt actually have the disease  they had other forms of dementia or even other medical conditions. That doesnt give an accurate picture of whether a potential treatment might help and the new definition aims to improve patient selection by using brain scans and other tests.  Better tests Many other diseases such as diabetes already are defined by measuring a biomarker an objective indicator such as blood sugar. That wasnt possible for Alzheimers disease until a few years ago when brain scans and spinal fluid tests were developed to do this. They measure certain forms of two proteins  amyloid and tau  that form plaques and tangles in the brain  and signs of nerve injury degeneration and brain shrinkage. The guidelines spell out use of these biomarkers over a spectrum of mental decline starting with early brain changes through mild impairment and Alzheimers dementia. What to do People may be worried and want these tests for themselves or a family member now but Jack advises Dont bother. Theres no proven treatment yet.  You might find a doctor willing to order them but spinal fluid tests are somewhat invasive and brain scans can cost up to . Insurance usually does not pay because theyre considered experimental outside of research. A large study is underway now to see whether Medicare should cover them and when. Anyone with symptoms or family history of dementia or even healthy people concerned about the risk can consider enrolling in one of the many studies underway. We need more people in this presymptomatic stage to see if treatments can help stave off decline Masliah said."