The Reading Room

Early Alzheimer’s detection: The next frontier for imaging screening?

by Miriam Sznycer-Taub

Definitively diagnosing Alzheimer’s disease has traditionally been challenging. While the disease is typically diagnosed from cognitive indicators, there has been no definitive way to verify the diagnosis until the patient died and an autopsy could be performed. As some evidence suggests that early diagnosis of the disease can result in better treatment outcomes, there has been a strong desire to develop better diagnostic tests.

While amyloid PET scanning has existed for some time, it has yet to become accepted as a diagnostic test for Alzheimer’s. This is likely due to the fact that there has not been convincing evidence that using amyloid PET imaging results in earlier diagnosis and better patient outcomes. But that may be changing, as a recent study reported that a combination of screening methods, including amyloid PET imaging, might allow doctors to diagnose Alzheimer’s earlier than before.

Combining multiple methods to achieve earlier diagnosis

PET scanning can identify amyloid plaques in the brain, a hallmark of Alzheimer’s disease, by visualizing radioactive tracer molecules that bind to these plaques. Amyloid can also be detected in spinal fluid and is considered a biomarker for Alzheimer’s. One focus for Alzheimer’s research has been studying the best combination of these biomarkers to advance diagnosis.

In a new study, published in the journal Brain, researchers measured amyloid levels in spinal fluid as well as used PET to measure amyloid plaques in the brain to see if either or both was a better determinant of Alzheimer’s. In a statement announcing the results of the study, the researchers explained that the best diagnosis of Alzheimer’s occurred when amyloid levels in the brain was compared with a ratio of two different types of amyloid found in spinal fluid.

Researchers noted that these results made an argument for the use of amyloid PET scans as part of Alzheimer’s diagnosis. The study coordinator noted “This may justify that, in some unclear cases, the diagnosis should include an amyloid PET scan to complement the cerebrospinal fluid sample.”

Widespread use of amyloid PET scans faces resistance, future research key to acceptance

Despite this promising study, there will likely be resistance to the widespread use of amyloid PET screening to diagnose Alzheimer’s. In 2013, the Centers for Medicare & Medicaid Services (CMS) released a National Coverage Decision noting that Medicare would not provide coverage for amyloid PET imaging. Alzheimer’s disease testing, specifically PET imaging, is included in Choosing Wisely as an imaging test whose necessity should be questioned or discussed.

In addition, the United States Preventive Services Taskforce (USPSTF) has not weighed in specifically on amyloid PET screening, but has given an “I” grade to the entire category of screening for cognitive impairment in older adults. This means that they found insufficient evidence to assess the benefits and harms of the screening. And inherent in PET scanning is radiation dose concerns, particularly for repeated imaging. All these factors have led to reluctance by payers, physicians, and patients to adopt amyloid PET imaging.

In response to the 2013 CMS National Coverage Decision, the Alzheimer’s Association, in collaboration with the American College of Radiology and the American College of Radiology Imaging Network designed a study to assess the impact of amyloid PET scanning on patient outcomes. Launched in 2015, the Imaging Dementia-Evidence for Amyloid Scanning (IDEAS) Study is currently enrolling 18,488 Medicare beneficiaries who meet the specific appropriate use criteria for amyloid PET scanning. CMS agreed to provide reimbursement for one amyloid PET scan per patient enrolled in the study. Researchers will be looking at the impact of amyloid PET imaging on both short and long term patient outcomes, as well as how the scans impact the use of health care resources and services.

As this study is still in its initial stages, researchers have not released any results. The results of the IDEAS study, and others like it, will be crucial in determining if amyloid PET imaging does lead to earlier Alzheimer’s detection and improved outcomes. Without these benefits, it’s unlikely that CMS and other payers will agree to provide for amyloid PET screening as a covered benefit.

Time will tell if amyloid PET screening gains a foothold in the imaging screening market. As we transition to a value-based care environment, there is increased emphasis in identifying screening programs that can diagnose disease earlier to reduce overall costs of care. If evidence suggests that amyloid PET screening can diagnose Alzheimer’s earlier, and result in better patient outcomes and lower costs of care, it could become an established imaging screening program.

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