Could Half of Alzheimer's Cases Be Misdiagnosed?

Roughly half of the people who are told they have Alzheimer's disease may in fact have other forms of dementia that produce similar symptoms, according to a new study.

Doctors have known for some time that the confusion and memory loss caused by the brain lesions associated with Alzheimer's can also be caused by other types of brain changes, such as tissue damage stemming from strokes. The study suggests that it may be even harder than previously thought to identify the source of dementia while a patient is still alive, says lead researcher Lon White, MD.

Identifying Different Types of Brain Lesions

"There are at least five different kinds of important lesions which can produce a picture that looks like Alzheimer's," says Dr. White, a professor of geriatric medicine at the University of Hawaii in Honolulu. "Each of those five kinds of lesions is apparently driven by its own pathologic process, and having one doesn't protect you from having others. All are independent and all are increasing with age."

Dr. White and his colleagues performed brain autopsies—the only surefire way of diagnosing Alzheimer's—on more than 400 elderly Japanese-American men. Only about half of those who had been diagnosed with Alzheimer's before death had the brain plaques that signal the disease. The occurrence of dementia in the other half appeared to have been caused by abnormal protein deposits (known as Lewy bodies), stroke-related tissue death (microinfarcts), cell damage, or some combination thereof.

Related: 9 Foods That May Help Save Your Memory

The researchers have since completed another 400 or so autopsies with similar results and will present their findings at the annual meeting of the American Academy of Neurology. Unlike studies published in medical journals, these findings are still preliminary and have yet to be thoroughly vetted by other experts in the field.

Diagnosing Alzheimer's

An Alzheimer's misdiagnosis doesn't have immediate consequences for the patient because no treatments exist that can stop the steady progression of the disease. And the drugs that, in some people, help slow Alzheimer's or make it more tolerable appear to work for other types of dementia, Dr. White says.

Patients and their families can nevertheless benefit from an early and accurate diagnosis. Ruling out other forms of dementia may help relatives plan for future care and determine their own risk for Alzheimer's, for instance.

Accurately diagnosing Alzheimer's is even more critical for research on potential treatments. Without knowing precisely who has Alzheimer's, pharmaceutical companies that have been developing new drugs "are not going to be able to see a true assessment of how effective their drug is," Dr. White says.

Related: 8 Weird Things Linked to Memory Loss Later in Life

Some promising advances in diagnosis have been made recently. A study published last year found that spinal fluid tests can predict Alzheimer's with a high degree of accuracy, and the Food and Drug Administration is currently weighing the approval of a brain scan that uses dye to highlight the plaques characteristic of Alzheimer's. The reliability of these methods needs to be confirmed, however.

"Everybody knows we need to do a better job of diagnosing," says Maria Carrillo, Ph.D., the senior director of medical and scientific relations at the Alzheimer's Association, a research and advocacy organization based in Chicago. "We are all trying to make that diagnosis better, earlier, faster. All of those things are currently underway in terms of the research study."