Utility of amyloid imaging for Alzheimer's remains uncertain

The clinical utility of amyloid-beta PET imaging for diagnostically evaluating Alzheimer's remains uncertain, according to an article published this month in the January issue of JAMA Internal Medicine.

Last September, the Centers for Medicare & Medicaid Services announced a decision that there isn't enough evidence to diagnose or treat individuals with dementia or neurodegenerative diseases. CMS approved beta-amyloid PET imaging under agency coverage for patients in approved clinical studies, or to exclude Alzheimer's disease in "narrowly defined and clinically difficult differential diagnoses," such as Alzheimer's and frontotemporal dementia.

The review summarized the findings of studies CMS used to support its decision. The authors, led by Steven D. Pearson, M.D., MSc, and colleagues, looked at 15 articles reporting on 15 studies focusing on amyloid-beta PET. Fourteen of the studies evaluated diagnostic accuracy and one evaluated the impact of testing on diagnostic impression.

Of the 14 evaluating diagnostic accuracy, 13 compared imaging results with clinical diagnoses or the "gold standard" of Alzheimer's diagnosis by biopsy.

A "pivotal study" that was submitted to the U.S. Food and Drug Administration compared the sensitivity and specificity of beta-amyloid PET with biopsy results, and included individuals 51 years or older who were judged by physicians to be near the end of life, as well as young healthy controls. Sixty-six percent of the individuals in the study population had Alzheimer's diagnosed via biopsy. Beta-amyloid PET with multiple readers had a median sensitivity of 92 percent and specificity of 95 percent. However, the ranges were from 69 to 95 percent for sensitivity, and 90 to 100 percent for specificity.

As reported in an article in Medscape, in addition to the fact there are relatively few studies on the subject, another limitation is that the evidence provided doesn't offer data on whether test results improve clinical management or patient outcomes. In addition, the available studies may not be representative of the patients who may be available for testing in clinical practice since they involved highly-trained physicians and patients who likely had Alzheimer's.

To learn more:
- see the article in JAMA Internal Medicine
- check out the CMS decision memo
- read the article in Medscape

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