Amyloid PET scanning may affect diagnosis of cognitive impairment

By Will Boggs MD

NEW YORK (Reuters Health) - Amyloid PET scanning with florbetapir F-18 may affect the diagnosis and drug treatment of patients with cognitive impairment, according to results from the INDIA-FBP study.

Amyloid PET scanning has shown promise as a pathophysiologic marker for diagnosing Alzheimer disease (AD), but its clinical usefulness remains uncertain, researchers say.

Although about seven out of eight AD patients have positive scans, so do almost a quarter of healthy elderly individuals, Dr. Marina Boccardi of the University of Geneva, Switzerland, and colleagues note in JAMA Neurology, online October 31.

The team quantified the effect of amyloid PET on the routine clinical diagnostic assessment of 228 individuals aged 50 to 85 years with cognitive abnormalities.

Positive scan results were more common among people with a pre-scan diagnosis of AD than among those with non-AD diagnoses.

Diagnostic changes were made in 79% of patients with a previous diagnosis of AD and an amyloid-negative scan, compared to 53% of patients with other diagnoses and a positive scan.

When patients with frontotemporal lobar degeneration (FTLD) had a diagnostic change resulting from a positive scan, this invariably led to an AD diagnosis. There was greater variability in the final diagnoses among FTLD patients with a negative scan.

Amyloid imaging results significantly increased diagnostic confidence after both positive and negative results and for both AD and non-AD diagnoses, even when the diagnosis did not change from before the scan to after the scan.

Positive amyloid PET scan results led to introduction of cognition-specific medications in 65.6% of previously untreated patients, and negative results led to drug discontinuation in 33.3% of previously treated patients.

"Studies ongoing in the United States and Europe (Imaging Dementia-Evidence for Amyloid Scanning and Amyloid Imaging to Prevent Alzheimer's Disease) are expanding these observations on a larger scale and launching health technology assessments that will quantify cost-effectiveness of amyloid PET in clinical routine," the researchers conclude. "Future efforts will need to focus on direct comparisons of amyloid PET with other (most importantly, cerebrospinal fluid) biomarkers with the aim of defining diagnostic algorithms and guidelines."

Dr. Richard J. Caselli from Mayo Clinic Arizona in Scottsdale, who coauthored an editorial related to this report, told Reuters Health by email, "Physicians should understand the limits of biomarker tests. They do not rule out other causes, they simply assess a disease-specific biomarker. What matters is first diagnosing whether or not a patient's dementia syndrome represents a reversible (e.g., chronic autoimmune encephalopathy) or irreversible disease."

"If reversible, then true disease modification such as immunotherapy for an autoimmune encephalopathy is the order of the day," he said. "If irreversible, then symptom management for maximizing quality of life is the goal of treatment. A person could have a positive amyloid PET scan and still have a stroke, brain tumor, CNS infection, etc. That is what is most important to ascertain. Symptom management is the best compromise we can make only when we cannot fix the root cause."

"We should be encouraged with the amazing progress that molecular imaging has made," Dr. Caselli concluded. "We can image the neuropathological hallmarks of Alzheimer's disease with amyloid and now tau PET. We should not however allow our clinical eyes to be blinded by this seductive technology. A positive biomarker test does not rule out an unrelated and potentially reversible process, nor does a negative biomarker test mean symptom management should be abandoned."

Dr. Benjamin M. Kandel from the University of Pennsylvania in Philadelphia, who has studied biomarkers of AD, told Reuters Health by email, "One limitation of the study is that it only examines the reaction of non-academic physicians to an amyloid-beta scan, and as such, should be viewed more as a poll of current practices than as a study in the etiology of disease."

"Without further longitudinal follow-up," he added, "it's difficult to say from here alone whether amyloid-beta scans should be incorporated into standard clinical practice."

Dr. Boccardi did not respond to a request for comments.

SOURCE: https://bit.ly/2f7yz48 and https://bit.ly/2fiJY3O

JAMA Neurol 2016.