Lancet: Autopsies confirm florbetapir PET scans of Alzheimers plaques
The study, conducted by Christopher M. Clark, MD, of Avid Radiopharmaceuticals in Philadelphia, and colleagues, was an extension of the researchers’ previous work comparing imaging to autopsy findings. Previous studies have been small and did not establish the sensitivity or specificity of florbetapir PET tracers, according to the authors.
Clark et al’s initial study featured 35 participants, and the current study added to this number to raise the total participant count to 59. All participants had a life expectancy of less than six months at enrollment and an autopsy was conducted within two years of PET imaging with florbetapir. Five nuclear medicine physicians interpreted the florbetapir scans, and each was classified as amyloid positive or amyloid negative.
Scan interpretations were compared with amyloid pathology at autopsy, which was classified as either moderate/frequent plaques or sparse/no plaques. Results showed the sensitivity and specificity of florbetapir PET imaging for the detection of moderate/frequent plaques was 92 percent and 100 percent, respectively, among participants who had an autopsy within two years of imaging. An analysis of a subgroup of participants who underwent autopsy within one year of imaging revealed similarly high sensitivity and specificity of 96 percent and 100 percent, respectively.
“The results of this study validate the binary visual reading method approved in the U.S.A. for clinical use with florbetapir and suggest that florbetapir could be used to distinguish individuals with no or sparse amyloid plaques from those with moderate to frequent plaques,” wrote the authors.
In addition to the visual assessment of the florbetapir PET images, semiquantitative and SUVR assessments were also conducted and all assessment methods demonstrated a significant positive relation between amyloid burden on PET and at autopsy.
“PET imaging of amyloid alone does not establish a diagnosis of Alzheimer’s disease or other neurological disorders. However, taken together with other clinical information and results of diagnostic tests, florbetapir PET might be an aid to diagnosis,” wrote the authors.