PET scans, like this one, will soon help diagnose Alzheimer's disease. Currently the only way to positively diagnose Alzheimer’s Disease is through brain biopsy or postmortem autopsy, both unpleasant procedures. But last week, Eli Lilly and its wholly owned subsidiary, Avid Radiopharmaceuticals, announced FDA approval of Amyvid, a radioactive diagnostic agent used for brain imaging of beta-amyloid plaques. The presence of these plaques is a hallmark of Alzheimer’s Disease, among other cognitive impairments. Amyvid is tagged with a radioisotope that binds to the amyloid plaques and produces a positron signal, which is detected by a Positron Emission Tomography (PET) scanner and is used to create a brain image.

Lilly was quick to emphasize that this is not an Alzheimer’s diagnosis test. A negative Amyvid scan indicates sparse to no amyloid plaques are currently present, which is inconsistent with a neuropathological diagnosis of Alzheimer’s Disease and reduces the likelihood that the patient’s cognitive impairment is due to Alzheimer’s. Conversely, a positive Amyvid scan indicates moderate to frequent amyloid plaques are present, which may be indicative of Alzheimer’s, but may also be due to other neurologic conditions or mere old age in people with normal cognition. Thus, Amyvid may only be used to rule out Alzheimer’s in patients experiencing cognitive decline -- that is, having difficulty in forming clear, rational thoughts.

Amyloid plaques, a hallmark of Alzheimer's disease, shown in the cerebral cortex. The FDA’s approval of this brain-imaging agent is an encouraging step towards developing a diagnostic test. According to Daniel Skovronsky, president and CEO of Avid, it is currently estimated that one in five patients clinically diagnosed with probable Alzheimer’s disease during life do not end up having the disease pathology upon autopsy. Amyvid may assist physicians, in conjunction with other diagnostic evaluations, in ruling out Alzheimer’s Disease in patients experiencing cognitive impairment, so that appropriate therapies may be pursued.

Amyvid will become available in a limited number of radiopharmacy imaging centers this June, with the goal of more widespread distribution in the near future. The road to gaining FDA approval for Amyvid has been a long one, though. The idea for Amyvid originated with Avid when it was an independent company. Lilly acquired Avid in late 2010, with bonus payments contingent upon future regulatory and commercial milestones for the imaging compound.

Development progressed quickly after the acquisition completed, and last spring Eli Lilly was anticipating FDA approval for this molecular imaging agent, which Lilly thought could revolutionize Alzheimer’s diagnosis. But the FDA unexpectedly chose to accept an expert panel’s recommendation to reject the drug. The rejection focused on Lilly’s need to establish a reader training program for market implementation to ensure reader accuracy and consistency of interpretations for Amyvid scans. Lilly implemented such training programs, and the FDA has now approved the beta-amyloid detection agent for limited use.

Alzheimer’s disease has had a strong presence in the news over the past several months, between the Obama administration announcing a funding boost, the National Institute on Aging and the Alzheimer’s Association releasing new guidelines for classifying Alzheimer’s disease, and a known cancer treatment drug demonstrating efficacy in reversing Alzheimer’s symptoms in mice. The FDA’s approval of this negative diagnosis test presents yet another step towards fully understanding, and eventually treating and preventing, this terrible disease.