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Amyloid positron emission tomography (PET) imaging was associated with changes in diagnoses and medical management of patients with mild cognitive impairment or dementia of uncertain etiology, the of Medicare beneficiaries found.

Amyloid scans helped change diagnoses from Alzheimer's to non-Alzheimer's disease in 25% of cases and altered clinical management in nearly two-thirds of all patients in the study, reported Gil Rabinovici, MD, of the University of California, San Francisco, and co-authors in .

"This research demonstrates that the availability of amyloid PET imaging can have a significant impact on how physicians care for patients with memory loss and cognitive impairment," Rabinovici told 番茄社区.

"The scale of the clinical changes spurred by amyloid PET imaging was twice as great as we had anticipated," he added. "These results illustrate the need to make these tests more widely available to specialists in the community who care for these patients, so they can provide patients and caregivers with the best possible care plan."

Amyloid PET detects one of two hallmarks necessary to diagnose Alzheimer's disease; to confirm Alzheimer's disease, evidence of both are needed. The IDEAS (Imaging Dementia - Evidence for Amyloid Scanning) study was a collaborative effort involving Medicare, pharmaceutical companies, the Alzheimer's Association, and the American College of Radiology to meet third-party payer requirements for more evidence of the clinical utility of amyloid PET scans.

Amyloid PET scans are expensive -- about $4,000 to $5,000, though costs vary widely, Rabinovici noted -- and insurers, including Medicare, have been hesitant to pay without seeing clear clinical benefit. IDEAS was designed to evaluate whether amyloid PET changed clinical management and whether improved patient outcomes resulted. (The outcomes portion of the study is ongoing and will be reported at a later date.) Results from the trial, therefore, could spur Medicare as well as private insurers to finally provide coverage, which would likely make such testing routine for many if not most older individuals.

The study -- partly supported by the three companies selling currently approved amyloid PET tracers -- involved 946 dementia specialists at 595 U.S. sites, who enrolled 16,008 patients from February 2016 through September 2017. Specialists documented their diagnosis and management plan before PET scans and again 90 days after PET.

The primary outcome was to assess change in clinical management from pre-PET to post-PET, using a composite end point that incorporated changes in drug prescriptions and counseling about safety and future planning. The primary objective was to assess whether this end point changed in 30% or more of participants in both mild cognitive impairment and dementia subgroups.

Eligible participants were Medicare beneficiaries with a diagnosis of mild cognitive impairment or dementia established by a dementia specialist. Participants were required to meet that stated the etiology of cognitive impairment was unknown, Alzheimer's disease was a diagnostic consideration, and knowledge of PET results was expected to change diagnosis and management.

Of 16,008 registered participants, 11,409 completed study procedures and were included in the analysis. Median age was 75; about 51% were women, and 60.5% had a diagnosis of mild cognitive impairment at baseline.

Changes between the pre-PET and post-PET composite management end point occurred in 4,159 of 6,905 patients with mild cognitive impairment (60.2%) and in 2,859 of 4,504 patients with dementia (63.5%), significantly exceeding the pre-specified threshold of 30%. The etiologic diagnosis changed from Alzheimer's to non-Alzheimer's disease in 25.1% of participants and from non-Alzheimer's disease to Alzheimer's in 10.5%.

The most common change in clinical management involved Alzheimer's disease drugs, which changed in 43.6% of patients with mild cognitive impairment and 44.9% of dementia patients. Changes in counseling occurred in 24.3% of mild cognitive impairment patients and 20.7% of dementia patients. Physicians reported that PET results substantially influenced changes in clinical management in 85% of the changes they made.

These results support -- but, without randomization, do not prove -- a relationship between PET findings and post-PET changes in management, noted Clifford Jack Jr., MD, and Ronald Petersen, MD, PhD, both of the Mayo Clinic in Rochester, Minnesota, in an .

An important finding was the discrepancy between presumed etiology underlying impairment based on pre- and post-PET assessments, they observed. Amyloid PET results were negative in 36% of people who were presumed to have Alzheimer's disease as a major contributing etiology before PET. Conversely, they were positive in 52% of people with a pre-PET presumed non–Alzheimer's disease etiology.

"These data highlight the disconnect between presumed etiology of impairment based on syndromic presentation alone and the underlying biology based on biomarker or neuropathologic evidence and has important implications for future clinical trials," Jack and Petersen wrote. While positive amyloid PET alone is not completely diagnostic of Alzheimer's disease, an "abnormal amyloid PET scan result greatly increases the likelihood that Alzheimer disease is present," they added.

This study had other limitations, noted Rabinovici and co-authors. Its design and lack of control group limited whether management changes were attributable directly to PET. Patients knew upfront that PET results were expected to change diagnosis and management. The study also did not compare other Alzheimer's imaging or cerebrospinal fluid biomarkers.

IDEAS participants were predominantly non-Hispanic white and did not adequately reflect the diversity of Medicare beneficiaries or the population of the U.S. "We are developing a 'New IDEAS' trial which will recruit patients with a broader range of clinical presentations and reflect a more racially and ethnically diverse cross-section of the American public," Rabinovici said.

"I hope the results of the IDEAS study will ultimately lead insurers to provide coverage for amyloid PET imaging," he added. "Beyond purely clinical considerations, I think people with Alzheimer's disease deserve the opportunity to know what they are facing and to make informed plans for the future with their families and loved ones."