New dye may lead to earlier Alzheimer's diagnosis

(CBS News) A new radioactive dye may change how Alzheimer's disease is diagnosed and could potentially catch the degenerative disease earlier than ever.

Typically a doctor will diagnose Alzheimer's in patients when certain symptoms such as memory or cognitive decline are present and other conditions are ruled out, since physical signs of Alzheimer's are often not present on MRI or other scans until later stages of the disease.

With the help of this new dye, called florbetapir (Amyvid), researchers at Duke University were able to detect early evidence of the disease in patients with mild or no cognitive impairment.

For the study, researchers tested the recently FDA-approved dye on 151 people, 69 of which had normal cognitive function, 51 who had been diagnosed with mild cognitive impairment, and 31 who already had Alzheimer's dementia.

The researchers used Positron Emission Tomography, or a PET scan, which uses radioactive dyes to create a 3D model of an organ's function. The dye is supposed to bind to amyloid plaques, which are a buildup of plaque that is a physical marker of Alzheimer's disease.

After scanning these patients at the study's beginning, the researchers followed up at 18 months and at 36 months into the study and found that patients who had evidence of plaque buildup on the initial PET scan did worse on cognitive tests than people who had no evidence of plaque at the trial's start. The study also revealed that 29 percent of patients with plaque on their scans developed Alzheimer's, compared to 10 percent of patients who started with no plaque.

For patients who were cognitively normal at the beginning of the study but had plaque on their initial scans, they too showed more mental decline at the 18-month follow-up. The findings are published online July 11 in Neurology. Final 36-month data will be presented this week at the Alzheimer's Association International Conference in Vancouver, Canada. The study was funded by Eli Lilly/Avid Radiopharmaceuticals, which markets the new dye.

The early detection of plaques that may predict cognitive decline could help guide care and treatment decisions for patients.

"Even at a short follow-up of 18 months we can see how the presence of amyloid plaques affects cognitive function," study co-author Dr. P. Murali Doraiswamy, professor of psychiatry at Duke, said in a press release. "Most people who come to the doctor with mild impairment really want to know the short-term prognosis and potential long-term effect."

However that knowledge could be devastating for people diagnosed early with the disease. Currently there is no cure for Alzheimer's and only two drugs on the market. There are three experimental drugs that are among the last ones remaining in final-stage trials, but if those results are negative, drug-makers may consider leaving the costly field out of frustration.

"For the most part we have been blind about who would progress and who wouldn't, so this approach is a step toward having a biomarker that predicts risk of decline in people who are experiencing cognitive impairment," Doraiswamy said.

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