On Thursday, the panel voted 16 to 0 to recommend approval of the imaging agent, known as Amyvid, with one critical caveat: Manufacturer Eli Lilly and Co. must demonstrate that standards for interpreting brain scans that show amyloid plaques illuminated by Amyvid can be made consistent enough to routinely guarantee an accurate diagnosis.
Amyvid (florbetapir) is injected into patients who then undergo a PET scan; a negative result can help rule out Alzheimer's, according to Lilly.
Experts agreed that the test could become a critical part of spotting Alzheimer's before symptoms have taken hold, but they noted that the clinical reality of that is far from imminent.
"It may well be that amyloid imaging will join colonoscopy, mammography, etc. as mid-life surveillance tests, and that anti-amyloid interventions are most effective in the pre-symptomatic stages of Alzheimer's disease," said Dr. Sam Gandy, the Mount Sinai Chair in Alzheimer's Disease Research in New York City. However, this possibility is years away, he added.
The value for research is clear, Gandy said. "Either a spinal fluid amyloid test or an amyloid scan will help weed out non-Alzheimer's dementias in clinical trials of anti-amyloid agents. The clinical value in the short-term is less obvious."
Current medications are most effective in the early stages of Alzheimer's, and amyloid scans might identify those patients for doctors who don't have access to neuropsychological testing, Gandy said.
"A confirmed diagnosis would enable planning for the future while patients are at an early enough stage to still participate in the discussion," he said. "In the symptomatic patient, the amyloid scan would portend the onset of dementia within the next five years."
However, because there is no cure for Alzheimer's disease yet, the test might be one that is not considered worth its cost, Gandy said.
Gandy noted that the "300-pound gorilla in the room" is whether Medicare/Medicaid will reimburse such a test, even if the FDA follows its expert panel's advice and approves Amyvid. (While the FDA doesn't have to follow a panel's advice, it usually does.) "Medicare may decide that the added value does not merit reimbursement without a meaningful intervention," he said.
Also, Grandy said he doesn't expect approval until there are methods in place to train doctors in how to read these scans.
Another expert, David Loewenstein, a professor of psychiatry and behavioral sciences and neurology at the University of Miami Miller School of Medicine, said that the approval of Amyvid "will allow physicians to come to an earlier diagnosis of Alzheimer's."
What is needed is consistency for evaluating scans using the agent, he said, so that physicians "can apply a single standard and there won't be gaps between hospitals because of different readers using different methods."
Loewenstein thinks use of this new diagnostic tool will help in several ways. First, it will help researchers find effective treatments by diagnosing the disease early, although having the plaques does not always mean the patient has Alzheimer's. Second, it will identify people who can take part in clinical trials of new Alzheimer's drugs.
"There is a whole new line of drugs being formulated that will help treat the earliest stages of the disease," Loewenstein said. "We need to know who are the appropriate people with the mildest cognitive problems to get into clinical trials."
In addition, the test has value even before treatments are available in terms of helping patients prepare for the course of the disease, Loewenstein noted. "I think many people would like an early diagnosis," he said.
For more information on Alzheimer's disease, visit the Alzheimer's Association.