A new study published in Alzheimer Disease & Associated Disorders could shed some light on the potential impact of PET amyloid imaging in the clinical setting.

According to the study, most clinicians had more diagnostic confidence after seeing amyloid PET scans when diagnosing Alzheimer's and related dementia. And, in a somewhat surprising finding, the assurance actually reduced the physicians' intention to use other testing modalities, such as MR and CT, particularly for patients who had not yet completed their diagnostic work-up.

"This study shows that this test may help physicians in decreasing additional testing, in modifying treatment plans and in how they cast their discussions with both patients and their caregivers because of the increase in diagnostic certainty," Dr. Peter Herscovitch, vice president-elect of the Society of Nuclear Medicine and Molecular Imaging (SNMMI), told DOTmed News.
To date, the imaging agent used in this study — florbetapir PET — as well as others, has only been used for validation purposes, and in research to better understand aging and dementia.

Florbetapir, or Amyvid, is a manufactured by Eli Lilly & Co., and was just approved for sale in the United States by the Food and Drug Administration in April. The Medicare Evidence Development & Coverage Advisory Committee (MEDCAC)is expected to hold a meeting to consider coverage for the imaging agent at the end of January 2013.

"It's [florbetapir PET] just at the cusp of beginning to gain acceptance. Not because there is a problem with the tracer, but because that's just where things are. It's a new modality and there has to be a better understanding of its appropriate use," said Herscovitch.

In fact, efforts are underway to do just that. The Alzheimer's Association and SNMMI have a joint partnership, the Alzheimer's Association-SNMMI Amyloid Imaging Taskforce, to figure out which indications and clinical scenarios would be appropriate for the use of amyloid agents in specific patient groups.

Study caveats

In the study, a total of 229 subjects at various medical centers across the United States underwent florbetapir PET scans between July 25, 2011 and May 29, 2012, before the imaging agent was approved by the FDA. The study looked at two groups: those who completed evaluation for cognitive decline within the past 18 months, and those who were currently undergoing an evaluation.

According to the study, subjects with mild impairment (without dementia) were more likely to have a negative scan than those with dementia, and 79 percent of the negative scans were in subjects without dementia. In addition, the results had the greatest impact on planning further diagnostic testing for the group that was undergoing evaluation. "In this group, there was a reduction in proposed testing after both positive and negative florbetapir PET scans," stated the study authors. Plans for CT or MR scans were reduced by 65 percent after a positive scan and by 40 percent after a negative scan, said the study.

But one caveat to consider with the results, said Herscovitch, is the exact point at which patients were undergoing evaluation. He said that if those patients were in the early stage of the process, and the amyloid scan provided a lot of confidence, then the physician might not suggest further testing. But if the patient was in the end of evaluation, there would be less of a decrease in the use of further testing.

"So it really depends when, in the diagnostic evaluation," said Herscovitch.

The study also noted that the question to physicians of what they planned to do, rather than what they actually did, was a major limitation.

Herscovitch said this is impetus for further study in day-to-day clinical settings.

"The community is happy to have this study, but it's only a first step."

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