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Diagnosing Dementia: Where We Are Now

- Tuesday, May 10, 2011

In this excerpt from a recent issue of Health After 50, Marilyn Albert, Ph.D., director of the Johns Hopkins Alzheimer’s Disease Research Center, talks about current methods of diagnosing Alzheimer's Dementia.

•   Traditionally, how has Dementia been diagnosed? How accurately can it be diagnosed today?

Research now tells us that Dementia progresses over time and likely begins years or decades before symptoms first appear. But right now, we can only diagnose Dementia late in the game. 

To diagnose Dementia we rule out other potential causes for cognitive decline, such as stroke, tumor or metabolic syndrome (a combination of medical disorders that raises the risk of heart disease, diabetes and stroke that may also increase the risk of dementia).

We then run a battery of cognitive tests and brain scans to rule out other neurological disorders and to determine whether the pattern of symptoms seems consistent with Dementia. If these things match up, we can give a probable diagnosis of Dementia. At major medical centers, a probable Alzheimer's Dementia diagnosis can be 80 to 90 percent accurate.

•   What are biomarkers, and how will they help with earlier, more accurate diagnosis of Dementia?

"Biomarker" is a term that describes a measurable change in a person that will give us information about what is going on in his or her brain tissue. For example, the signature of Alzheimer’s disease includes amyloid plaques [abnormal accumulation of amyloid proteins] and neurofibrillary tangles (deposits of defective tau proteins, a type of protein abundant in the brain).

The proteins related to the plaques and tangles are present in the spinal fluid of patients with Dementia. They’re also present in those with mild cognitive impairment (MCI) -- slight problems in thinking, learning and remembering that sometimes progress to full-blown dementia.

The proteins serve as biomarkers of the progressive changes taking place in the brain. In clinical research, tau and amyloid have been shown to predict the progression of patients with MCI to Dementia and ultimately Alzheimer's.

In other words, measuring these proteins allows us to say more accurately and at an earlier stage of disease that we are pretty sure this person is going to develop Alzheimer’s dementia. Imaging procedures, such as PET (positron-emission tomography) and MRI (magnetic resonance imaging), also can provide information about the pathology present in the brain. For example, amyloid can now be measured with PET.