Currently, clinicians use several tools to diagnose “possible AD” or “probable AD” in a patient who is having difficulties with memory or other mental functions. These tools include a patient history, physical exam, laboratory tests, brain scans, and a series of tests that measure memory, language skills, and other abilities related to brain functioning. However, in these patients, AD can be diagnosed conclusively only by examining the brain after death in an autopsy to determine the presence of characteristic plaques and tangles in certain brain regions.
The earlier an accurate diagnosis of AD is made, the greater the gain in managing symptoms and determining the natural history of AD. An early, accurate diagnosis of AD is especially important to patients and their families because it helps them plan for the future and pursue care options while the patient can still take part in making decisions.
Researchers have made significant progress in developing accurate diagnostic tests and techniques that can be used in living patients. In specialized research facilities, clinicians can now diagnose AD with up to 90 percent accuracy. For example, work is underway to develop new tests of mental status that might be used to distinguish between people who might have very early AD symptoms and those experiencing age-related normal memory loss. Other investigators have explored the utility of analyzing cerebrospinal fluid for levels of “sticky” beta-amyloid and tau for diagnosing AD. Researchers also have used positron emission tomography (PET) scans, an imaging method in living patients, to see whether they can detect changes in the way glucose is metabolized in parts of the brain that are most affected by AD. Another imaging method, known as single photon emission computed tomography (SPECT), also has been combined with genetic and psychological testing to predict which people with memory problems eventually will develop clinically diagnosed AD.
A particularly exciting area of work involves yet another imaging technique in the diagnosis of AD. This technique uses magnetic resonance imaging (MRI) to measure the size of various structures in the brain. Many studies have shown that AD causes some brain structures, particularly the hippocampus, to shrink early on in the disease, and scientists are exploring exactly how early this shrinkage, or atrophy, can be detected. Several teams of NIA-funded scientists have established the usefulness of MRI as a tool to help determine which people with memory problems are in the earliest stages of AD; to identify people who will later be diagnosed with AD; and to measure hippocampal volume to distinguish between people with mild cognitive impairment (MCI) and those with no memory or learning problems, and between people without AD and those with very mild AD.
National Institutes of Health
National Institute on Aging
1999 PROGRESS REPORT ON ALZHEIMER’S DISEASE