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By the way, doctor: Can brain scans be used to diagnose Alzheimer's disease?

By the way, doctor

Can brain scans be used to diagnose Alzheimer's disease?

Q. Is there a brain scan that can specifically diagnose Alzheimer's disease?

A. As of late 2005, there is no diagnostic scan for Alzheimer's disease. Currently, the first step in making the diagnosis is testing to determine the type and extent of the person's dementia. These cognitive tests consist of a series of questions designed to assess short-term recall, spatial sense, and other basic elements of thinking. The one that's used most often is called the Mini-Mental State Examination.

After that exam, diagnosis is mainly a process of elimination. Doctors order a battery of blood tests to rule out anemia, low levels of thyroid hormone, vitamin B12 deficiency, and other conditions that might cause confused or clouded thinking. A CT or MRI scan might be ordered to make sure the person doesn't have a tumor, damage from a stroke, or a brain injury of some other kind.

Studies comparing autopsy results to Alzheim­er's disease diagnoses made in this way have shown that they're remarkably accurate, correctly classifying people 85%–90% of the time. Still, doctors, patients, and families would like to have a more direct and reliable way of diagnosing Alzheimer's that would also quantify how far it has progressed.

A PET scan involves intravenous injection of a substance necessary for brain function (usually glucose) that has been combined (or "tagged") with a compound that is temporarily radioactive. When this combination, or "tracer," gets into the brain, metabolically active regions "light up" on the scan.

Many Alzheimer's researchers believe the cause of the disease is the accumulation of beta-amyloid protein in areas of the brain that are important for thinking. University of Pittsburgh researchers have developed a special tracer that zeroes in on these beta-amyloid deposits. In 2004, they and their Swedish colleagues reported results of a PET scan study using this tracer. Comparing people with mild or moderate Alzheimer's to healthy volunteers, they found that the tracer was much more evident in the Alzheimer's patients and pro­duced a measurable signature of beta-amyloid buildup in the brain.

Because of this study and others, I think PET scans represent our best bet for identifying early Alzheimer's disease. But much more research needs to be done before they become part of routine clinical care.

— Dennis J. Selkoe, M.D. Brigham and Women's Hospital Harvard Health Letter Editorial Board

Last updated:	September 05, 2008