FDA to consider Alzheimer's test for living patients

One of the many frustrations of Alzheimer’s disease is the difficulty in pinpointing just who has it. According to published research, as many as one in five people told they have Alzheimer’s are mislabeled. A definitive diagnosis can  be made only after death, by an autopsy that reveals a distinctive buildup – known as amyloid plaques – in the patient’s brain. This week, however, the FDA will consider a new diagnostic test that may be able to identify those plaques through PET scans – a type of brain scan – on living patients.

In a small study run by Avid Radiopharmaceuticals and made public Tuesday in the Journal of the American Medical Association , PET scans identified the telltale plaques in 97 % of patients who actually had them, as determined by a subsequent autopsy. The 35 patients in this part of the study were terminally ill, and agreed to both a brain scan and an autopsy.

The researchers also performed PET scans on presumably healthy people to try to ensure that the test could tell the difference. It could. Of 74 young and healthy people tested, none had scans indicating Alzheimer’s.

Before performing a PET scan, a doctor or technician injects the patient with a radioactive dye that can be detected by the imaging equipment. The particular dye used in this test was developed by Avid and is known as Florbetapir F 18. Chief Executive Officer Dr. Daniel Skovronsky says Florbetapir F 18 binds tightly to the amyloid proteins – making them visible to the scanner – but doesn’t bind to other tissue.

According to Skovronsky, diagnosis of Alzheimer’s still depends on a clinician who can evaluate a patient’s overall condition, but he says the test with Florbetapir could be especially useful as a tool to rule out Alzheimer’s. In that scenario, a patient who shows symptoms of dementia would be given a PET scan; a negative result would push her physician to consider other conditions.

A second paper in JAMA suggests that a simple, low-cost blood test can tell whether a person is at risk for cognitive decline, which is a precursor to Alzheimer’s.

During a span of 10 years, researchers checked the blood of 997 elderly people in Memphis, Tennessee and Pittsburgh, Pennsylvania, testing for two types of proteins that are associated with Alzheimer’s. They re-tested each person at 1-year, 3-year, 5-year, 8-year and 10-year intervals. Patients with lower levels were significantly more likely to suffer cognitive decline over time.

Researchers also found that patients with more “cognitive reserve” while healthy, are less likely to decline. “Cognitive reserve” is measured in various ways – for example, by years of school attended, or performance on intelligence tests.  The researchers say it may be that people with higher intelligence or more education are able to better compensate for functions lost to early cognitive decline.