Practical utility of amyloid and FDG-PET in an academic dementia center

Abstract

Objective: To evaluate the effect of amyloid imaging on clinical decision making.

Methods: We conducted a retrospective analysis of 140 cognitively impaired patients (mean age 65.0 years, 46% primary β-amyloid (Aβ) diagnosis, mean Mini-Mental State Examination 22.3) who underwent amyloid (Pittsburgh compound B [PiB]) PET as part of observational research studies and were evaluated clinically before and after the scan. One hundred thirty-four concurrently underwent fluorodeoxyglucose (FDG)-PET. We assessed for changes between the pre- and post-PET clinical diagnosis (from Aβ to non-Aβ diagnosis or vice versa) and Alzheimer disease treatment plan. The association between PiB/FDG results and changes in management was evaluated using χ(2) and multivariate logistic regression. Postmortem diagnosis was available for 24 patients (17%).

Results: Concordance between scan results and baseline diagnosis was high (PiB 84%, FDG 82%). The primary diagnosis changed after PET in 13/140 patients (9%) overall but in 5/13 (38%) patients considered pre-PET diagnostic dilemmas. When examined independently, discordant PiB and discordant FDG were both associated with diagnostic change (unadjusted p < 0.0001). However, when examined together in a multivariate logistic regression, only discordant PiB remained significant (adjusted p = 0.00013). Changes in treatment were associated with discordant PiB in patients with non-Aβ diagnoses (adjusted p = 0.028), while FDG had no effect on therapy. Both PiB (96%) and FDG (91%) showed high agreement with autopsy diagnosis.

Conclusions: PET had a moderate effect on clinical outcomes. Discordant PiB had a greater effect than discordant FDG, and influence on diagnosis was greater than on treatment. Prospective studies are needed to better characterize the clinical role of amyloid PET.

Figures

Figure. Concordance between pre-PET clinical diagnosis and PET results

Numbers refer to number of subjects. (A) Concordance between specific clinical diagnoses and PET. (B) Concordance vs level of impairment, stratified by CDR. (C) Concordance vs age at onset. Significant differences in concordance are indicated with respective p values. AD = Alzheimer disease; bvFTD = behavioral variant frontotemporal dementia; CBS = corticobasal syndrome; CDR = Clinical Dementia Rating; FDG = fluorodeoxyglucose; MCI = mild cognitive impairment; PiB = Pittsburgh compound B; PPA = primary progressive aphasia.