Only recently has it become possible to create high-quality images of the brain plaques characteristic of Alzheimer's disease in living people through positron emission tomography (PET). Even so, questions remain about what can be learned from these PET images and which people should have this test.
To provide guidance for physicians, individuals and families affected by Alzheimer's, and the public, the Society of Nuclear Medicine and Molecular Imaging (SNMMI) and the Alzheimer's Association have jointly published the first criteria for the appropriate use of this imaging technology to aid in the diagnosis of people with suspected Alzheimer's disease. The criteria were published online January 28 as an article "in press" by Alzheimer's & Dementia: The Journal of the Alzheimer's Association and "ahead of print" in The Journal of Nuclear Medicine.
"Our primary goal is to provide healthcare practitioners with the information and options available to provide patients with the best possible diagnosis and care in a cost effective manner," said Maria Carrillo, Ph.D., Alzheimer's Association vice president of Medical and Scientific Relations.
Appropriate Use Criteria (AUC) for Brain Amyloid Imaging with PET in Alzheimer's
While elevated beta amyloid plaques are one of the defining pathologic features of Alzheimer's, many elderly people with normal cognition also have elevated levels of these plaques, as do people with conditions other than Alzheimer's dementia. Therefore, the potential clinical use of amyloid PET requires careful consideration so that its proper role may be identified.
To develop the new criteria, the Alzheimer's Association and SNMMI assembled an Amyloid Imaging Taskforce (AIT) consisting of dementia and imaging experts to review the scientific literature and develop consensus recommendations for the clinical use of this promising new technology.
The AIT concluded that amyloid imaging could potentially be helpful in the diagnosis of people with cognitive impairment when considered along with other clinical information, and when performed according to standardized protocols by trained staff. In addition, they emphasized that the decision whether or not to order amyloid imaging should be made only after a comprehensive evaluation by a physician experienced in the assessment and diagnosis of cognitive impairment and dementia, and only if the presence or absence of amyloid would increase certainty in the diagnosis and alter the treatment plan.
According to the AIT, appropriate candidates for amyloid PET imaging include:
Inappropriate candidates for amyloid PET imaging include:
Amyloid PET imaging is also inappropriate:
"As amyloid imaging becomes more prevalent in clinical settings, medical professionals must understand how to appropriately utilize the test," said Frederic H. Fahey, D.Sc., SNMMI president. "Neurology and dementia experts should order the test only when appropriately indicated, and nuclear medicine and molecular imaging professionals must ensure they have been adequately trained to interpret the results of the scan. Working together, we hope that the information garnered from amyloid PET imaging will aid in diagnosis and play a pivotal role in the development of new treatments for Alzheimer's."
The taskforce acknowledged that the healthcare provider makes the ultimate judgment regarding the care of each patient. The AIT sought to assist this process and identified the following general sequence of events for the use of amyloid PET according to the new criteria:
Although identifying potential benefits, the AIT concluded that amyloid PET results will not constitute and is not equivalent to a clinical diagnosis of Alzheimer's disease dementia. They said that imaging is only one tool among many that clinicians should use judiciously to manage patients, and that amyloid PET imaging does not substitute for a careful history and examination.
"Because both dementia care and amyloid PET technology are in active development, these new appropriate use criteria will require periodic reassessment and updating," Carrillo said.
PET Amyloid Imaging in Alzheimer's -- An Overview
PET uses radiopharmaceuticals (radioactive drugs) to produce three-dimensional functional images of the brain or other body part. In amyloid PET imaging, the radiopharmaceutical is introduced into the body by injection into a vein and binds specifically to the amyloid protein, enabling visualization of areas in the brain where amyloid has clumped together into plaques. One of the new PET compounds was approved for general use by the U.S. Food and Drug Administration in April 2012.
Amyloid imaging is not covered by insurance at this time, and costs for the scan are "out of pocket." While costs of amyloid PET are not yet established, and PET costs in general can vary depending upon location, other PET scans are known to cost between $1,000 and $3,000, or more. Nonetheless, the AIT concluded that the proven sensitivity and specificity of the new radiopharmaceuticals for brain amyloid and the known association between brain beta amyloid deposition and Alzheimer's suggest these new radiopharmaceuticals could potentially be helpful in the workup and diagnosis of patients with cognitive impairment.
Materials provided by Society of Nuclear Medicine. Note: Content may be edited for style and length.
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