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Amyloid brain scans can change diagnosis and treatment choice in patients with cognitive impairment, but debate about clinical utility is far from over, researchers reported.

In the INDIA-FBP study of 228 patients clinically diagnosed with cognitive impairment in Italy, 46 patients previously diagnosed with Alzheimer's (79%) were negative on amyloid PET with [¹⁸F]-Florbetapir, and 16 (53%) of those with non-Alzheimer diagnoses had positive scans -- resulting in changed diagnoses, according to , of the University of Geneva, and colleagues.

Altered diagnoses resulted in changed prescriptions: about 66% of patients with positive scans were started on acetylcholinesterase inhibitors, while 33% of those with a negative scan were taken off those drugs, they .

Yet the researchers cautioned that the effect of amyloid PET scanning on morbidity and mortality, as well as its cost-effectiveness, remains to be assessed.

"Although the current impact of amyloid PET is debatable owing to a lack of disease-modifying drugs, future therapies may need to leverage on amyloid PET results," they wrote. "At present, more accurate etiologic diagnosis and targeted drug treatment are justified by reports of adverse events in patients treated with cholinesterase inhibitors and of ineffectiveness for cognitive impairment of vascular etiology."

In an accompanying editorial, and , of the Mayo Clinic in Scottsdale, Ariz., posed this question: "Does the ability to modestly increase diagnostic confidence in distinguishing between several equally degenerative diseases and, in turn, jockey marginally effective symptomatic medications justify this added cost to an already expensive disease?"

Proving the clinical value of amyloid PET scans became a topic of particular interest in 2013 when the Centers for Medicare and Medicaid Services declined to allow coverage under Medicare, citing a lack of evidence that the scans improve patient outcomes. And it's unclear that this study will change the agency's mind.

The study, conducted at 18 centers in Italy, included patients (mean age 71, 46% male) diagnosed and referred by community health practitioners. Diagnoses included Alzheimer's disease, frontotemporal lobar degeneration (FTLD), and subcortical disease (including cardiovascular disease, Parkinson's dementia, and corticobasal degeneration).

The prevalence of positive scan results was greater among patients with a pre-scan diagnosis of Alzheimer's than in those with non-Alzheimer's diagnoses (P=0.03). However, positive scans were noted in patients clinically identified as having non-Alzheimer's disorders, including 49% diagnosed with FTLD and 46% diagnosed with subcortical disease.

Among non-Alzheimer's diagnoses, a positive amyloid PET resulted in a change of diagnosis in 72% of patients thought to have FTLD and in 25% of those thought to have subcortical disease, they reported.

Overall, 123 of 137 patients (90%) with amyloid-positive results received a final diagnosis of Alzheimer's disease, and 79 of 91 (87%) of those with amyloid-negative results were ultimately told they didn't have Alzheimer's.

The researchers also found that amyloid PET evaluation honed clinicians' confidence in their diagnosis of Alzheimer's, which increased by 15% for patients with an amyloid-positive scan and decreased by 30% for those with an amyloid-negative scan (P<0.001 for both), the researchers found.

The study was limited by a lack of fully standardized diagnostic procedures, which precluded assessment of variations in the utility of amyloid PET depending on selection of pre-scan investigations. Similarly, the study design did not control for physician differences in terms of experience, education, and beliefs in the role of amyloid in Alzheimer's etiology, the researchers said.

, of the Mayo Clinic in Rochester, Minn., who wasn't involved in the study, told MedPage Today that while families may value certainty in diagnosis "because it gives them closure ... that might not translate into much objective change in outcomes or course" given that current treatments "have very modest and unfortunately evanescent benefits."

Based on his own experience in studies involving amyloid PET scans, Knopman suggested that their use in research could help physicians become more savvy about the diagnosis of Alzheimer's. However, this topic is essentially moot in the U.S. because amyloid PET scans are not covered by any insurance.

A consortium assembled by the American College of Radiology is currently enrolling patients in the to address the value question.

Zaven Khachaturian, PhD, editor-in-chief of Alzheimer's & Dementia, agreed that the current value of an amyloid PET scan is "in the area of clinical trials for treatment, where this technology could become very valuable to better stratify the study population into the various arms of treatment studies."

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