FYI Daily

Putting New Alzheimer's Test in Perspective

Last updated: Apr 10, 2012

PET scan

The words "new," "Alzheimer's," and "test" strung together can cause a lot of excitement and hope. A new brain scan test just approved by the Food and Drug Administration allows radiologists to see signs of Alzheimer's Disease early through a PET scan -- but its use, for now, will be fairly limited, warns Forbes.

In other words, there's still no single test that can diagnose Alzheimer's. The average doctor and consumer are still left with the existing main options for Alzheimer's testing, which each have pros and cons.

The new test uses a chemical called florbetapir (Amyvid), which binds to amyloid plaques in the brain so they can then be seen on a scan. Amyloid plaques are a hallmark component of Alzheimer's. Patients who show no signs of plaque probably don't have Alzheimer's disease. Before the development of imaging agents, amyloid could only be seen after death, via autopsy.

Unfortunately, the presence of amyloid plaques doesn't necessarily mean that disease is present. Some 20 percent of older adults who were healthy and had no sign of cognitive impairment are found to have amyloid plaques in their brains during autopsy. The presence of plaques plus already-notable memory and cognitive declines are what point to probable disease. (So this test can't reveal Alzheimer's in pre-symptomatic patients.)

The test itself is also subjective. Last year, the F.D.A. rejected the imaging agent because it said maker Eli Lilly "needed a better training program in place to make sure different doctors come to similar conclusions when they read the scans," reports Forbes science and medicine reporter Matthew Herper.

And it's expensive: $1600, wholesale.

The likeliest use of the Amyvid test is as a research tool, in the screening of subjects for the testing of new drugs. "If drug companies can screen out patients who are likely not to have Alzheimer's, they are far more likely to be able to show that medicines aimed at Alzheimer's are effective in clinical trials. Having those non-Alzheimer's patients in a study is going to wash out the efficacy of a new drug," Herper says.

Image by Flickr user Muffet, used under a Creative Commons license.