Amyloid Tracer Clinically Useful in Cognitive Impairment

Pam Harrison

December 04, 2012

Using positron emission tomography (PET) scans with a recently approved amyloid tracer to identify brain plaques is helpful in the diagnosis and management of patients with progressive cognitive impairment, new research shows.

Mark Mintun, MD, Avid Radiopharmaceuticals, Philadelphia, Pennsylvania, and colleagues found that PET imaging using florbetapir F18 showed amyloid deposits in 113 out of 229 patients being evaluated for progressive cognitive decline or impairment of uncertain etiology. The information provided by the scan then led physicians to change their diagnosis in approximately 55% of patients.

Results of florbetapir PET scans also contributed to at least 1 change in the prescan treatment plan in almost 87% of patients.

"The ability to see amyloid in the brain used to be only in the province of the pathology. This imaging technique gives us an opportunity to evaluate amyloid in living patients, and we found that the technology did change physicians' diagnosis over half of the time and also improved their confidence in the diagnosis," Dr. Mintun told Medscape Medical News.

"And while we don't have the outcome data in terms of what happened to patients, this will be addressed by future studies," he added.

The study was published online November 30 in Alzheimer Disease and Associated Disorders.

Changed Diagnosis

The study included roughly equal numbers of patients who had completed a diagnostic evaluation for progressive cognitive decline or impairment within the previous 18 months as well as those who were currently undergoing an evaluation.

Before ordering the PET scan, physicians recorded either the current diagnosis for those who had completed the diagnostic evaluation or the working diagnosis for those still undergoing evaluation.

Physicians were also asked to document a diagnostic testing and management plan using available information before patients underwent florbetapir imaging.

In roughly one half of the cohort, the florbetapir PET scan was positive.

Knowing results of the PET scan affected diagnostic thinking in 54.6% of the overall cohort.

When the provisional diagnosis was Alzheimer disease (AD), imaging results provoked a change in diagnosis in 37% of cases.

When it was either "indeterminate" or another cause of dementia, the diagnosis changed in over 60% of cases.

Either way, the scans increased the physicians' ratings of diagnostic confidence by approximately 20%.

Table: Change in Diagnosis From Before Scan to After Scan

  Prescan Diagnosis Postscan Diagnosis Postscan Diagnosis Postscan Diagnosis Change in Diagnosis
All participants Due to AD: n = 86 Due to AD: n = 54 Indeterminate: n = 22 Not due to AD: n = 10 37.2%
  Indeterminate: n = 122 n = 47 n = 42 n = 33 65.6%
  Not due to AD: n = 21 n = 12 n = 1 n = 8 61.9%


Changes in intended medication management were especially affected by the results of the scan, the researchers report.

In 31% of patients, results led to an intended change in AD medications; in 7.4% of patients, results led to an intended change in treatment with psychiatric medications.

"Changes in medication use were consistent with the changes in diagnosis," the authors write.

Physicians also intended to reduce the use of other testing modalities on receipt of scan results, especially for patients for whom the diagnostic workup had not yet been completed.

Clinical Utility

Reisa Sperling, MD, Harvard Medical School, Boston, Massachusetts, told Medscape Medical News that the study demonstrates for the first time that there may be clinical utility of PET amyloid imaging in helping guide doctors' decision-making in the workup and treatment of cognitive impairment and dementia.

"In particular, the change in 'diagnostic certainty' based on PET amyloid imaging results may be important to physicians by decreasing the need for additional testing and in discussing treatment plans with patients and their families," she said.

She agreed with study authors that additional studies are needed to understand the impact of PET amyloid imaging results on long-term clinical care for patients.

"But initial findings do suggest that PET amyloid imaging may be useful to physicians in some situations where the clinical diagnosis of Alzheimer's disease is uncertain," said Dr. Sperling.

The study was supported by Avid Radiopharmaceuticals. Dr. Mintun is an employee of Avid Radiopharmaceuticals, a wholly owned subsidiary of Eli Lilly and Company. Dr. Sperling reports no relevant financial relationships.

Alzheimer Dis Assoc Disord. Published online November 29, 2012. Abstract