Concordance Between Cerebrospinal Fluid Biomarkers and [C-11] PIB PET in a Memory Clinic Cohort

Background: Two approaches are available for measuring Alzheimer's disease (AD) pathology in vivo. Biomarkers in cerebrospinal fluid (CSF) include amyloid-beta(1-42) (A beta(42)) and tau. Furthermore, amyloid deposition can be visualized using positron emission tomography (PET) and [11C] Pittsburgh compound-B ([11C] PIB). Objective: We investigated concordance between CSF biomarkers and [11C] PIB PET as markers for AD pathology in a memory clinic cohort. Methods: We included 64 AD patients, 34 non-AD dementia patients, 22 patients with mild cognitive impairment (MCI), and 16 controls. [11C] PIB scans were visually rated as positive or negative. CSF biomarkers were considered abnormal based on A beta(42) alone ( <550 ng/ L), a more lenient A beta(42) cut-off ( <640 ng/ L) or a combination of both A beta(42) and tau ((373 + 0.82tau)/ A beta(42) > 1). Concordance between CSF biomarkers and [11C] PIB PET was determined Results: Overall, concordance between [11C] PIB PET and CSF A beta(42) ( <550 ng/ L) was 84%. In discordant cases, [11C] PIB PET was more often AD-positive than A beta(42). When a more lenient A beta 42 cut-point ( <640 ng/ L) or a combination of A beta(42) and tau was used, concordance with [11C] PIB PET appeared to be even higher (90% and 89%). This difference is explained by a subgroup of mostly MCI and AD patients with A beta 42 levels just above cut-off. Now, in discordant cases, CSF was more often AD-positive than [11C] PIB PET. Conclusion: Concordance between CSF A beta(42) and [11C] PIB PET was good in all diagnostic groups. Discordance was mostly seen in MCI and AD patients close to the cut-point. These results provide convergent validity for the use of both types of biomarkers as measures of AD pathology