Alzheimer's: It's a disease that afflicts over five million Americans, and there is currently no treatment for it. But researchers are getting closer to a diagnostic test for Alzheimer's disease. Last week a Food and Drug Administration (FDA) advisory committee recommended that the agency approve a brain scan that can detect the disease in a living patient.
The approval would be for a dye that homes in on plaque in the brain, making it visible on PET scans. Such scans would be especially valuable in a common and troubling situation — trying to make a diagnosis when it is not clear whether a patient’s memory problems are a result of Alzheimer’s disease or something else. If a scan shows no plaque, the problems are not caused by Alzheimer’s and could be from tiny strokes or other diseases. [New York Times]
Designed by Avid Radiopharmaceuticals, the radioactive marker florbetapir F-18 goes by the brand name Amyvid. The FDA advisory committee initially rejected the new drug with a 13-3 vote, but the committee later reversed its decision and unanimously recommended its approval, with one caveat: the company needs to develop clearer guides for doctors so that they can interpret the scans consistently. While many media outlets have hailed the test as a breakthrough, some critics think that Avid's test still has major kinks to be worked out.
While the test is considered safe, members of the FDA's Peripheral and Central Nervous System Drugs Advisory Committee said Avid needs to do more work training the medical professionals who would administer it. Panel members also voiced concern that there would be too many "false-positive" tests – in other words, too many patients told they have Alzheimer's when in fact they don't. Dr. James Tatum of the Hunter Holmes McGuire VA Hospital in Richmond cited data suggesting that in patients older than 80, as many as a third of "positive" test results would be wrong. [CNN]
Others argue that an imperfect test is better than no test at all--currently, the only way to discover Alzheimer's plaque buildups is via autopsy. And if doctors don't find the telltale plaque after scanning someone's brain, they'll be able to start looking for other diseases instead of remaining in it-could-be-Alzheimer's limbo. That's why some doctors see this scan as a breakthrough.
“This is a big deal,” said Dr. Pierre N. Tariot, director of the memory disorders center at the Banner Alzheimer’s Institute in Phoenix. Asked if he would be using the scans, Dr. Tariot replied, “Absolutely." ... The panel’s vote “has moved us a monumental step forward,” said Dr. Reisa Sperling, [director of the Center for Alzheimer’s Research and Treatment at Brigham and Women’s Hospital in Boston] adding that with the scans “we will not just be guessing clinically.” [New York Times]
Recently, a study published in The Journal of the American Medical Association further strengthened the case for this scan by finding a strong correlation between the scanning results and autopsy methods for finding plaque. The main elephant in the room now is a technicality:
... Avid's application actually does not seek approval to use the test to diagnose Alzheimer's disease. Rather, it seeks approval to use it to rule out the presence of amyloid plaques. If FDA eventually grants approval, presumably some doctors would use it for "off-label" purposes, such as testing people they already suspect have Alzheimer's or screening people with mild memory impairments. [ScienceNOW]
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