October 15, 2007

A New Test for Alzheimer's Disease: Hype or Hope?

The New York Times reported today on “a blood test” for Alzheimer’s disease (Andrew Pollack, “Progress Cited in Alzheimer’s Diagnosis,” NYT October 15, 2007). Is there actually such a test? If not, is one imminent?

Don’t hold your breath. I’m old enough to remember the eye drop test for Alzheimer’s and the skin biopsy for Alzheimer’s, neither of which panned out, not to mention the serum beta amyloid test and a few spinal fluid tests. What the news media are reporting appeared in the on-line edition of Nature Medicine yesterday in a letter-to-the-editor, not in a peer-reviewed article (Sandip Ray, Markus Britschgi, Charles Herbert et al, “Classification and Prediction of Clinical Alzheimer’s Diagnosis Based on Plasma Signaling Proteins,” Nature Medicine online, October 14, 2007). This means the findings have not been written up in an article and subjected to careful scrutiny by other scientists who are experts in the field. The letter, penned by 25 scientists, notes that the group has been studying over 100 different proteins found in the blood of patients with a diagnosis of Alzheimer’s disease to see if some combination of them might serve as a diagnostic test. They have found that a particular pattern involving 18 different proteins successfully classified 8 out of 9 patients with Alzheimer’s disease (confirmed at autopsy) as having the condition. The results, while interesting, are far too preliminary to be of interest to the general public.

If we did have a test that could accurately diagnose Alzheimer’s disease, would it matter to the millions of people with cognitive impairment and their families? Probably not. Right now, physicians can already diagnose Alzheimer’s disease with 90% accuracy, based on a careful history and physical examination together with existing laboratory tests. Even more crucial, while it is useful to diagnose dementia (whatever the cause) so as to begin planning for the future, it’s only important to distinguish Alzheimer’s disease from other forms of dementia to the extent that we have good treatments specific to Alzheimer’s. Today, the only “treatment” we have for early Alzheimer’s disease is a group of drugs known as cholinesterase inhibitors—drugs such as Donepezil (Aricept). This medicine can temporarily improve cognitive function a very modest amount. Its effectiveness is so questionable that the British NICE (National Institute for Health and Clinical Excellence) recommends against its use in patients with mild dementia (see my earlier blog posting, “Americans, Alzheimer’s, and Aricept,” February, 2006). It doesn’t cause any harm if it’s administered to patients who prove to have a non-Alzheimer’s dementia, such as vascular dementia.

One day, when we have good treatments for early Alzheimer’s disease, it will be important to make the diagnosis early and accurately. Today, what a good doctor can do is good enough.

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