Brain Amyloid-β Deposition and Blood Biomarkers in Patients with Clinically Diagnosed Alzheimer's Disease

Brain amyloid-beta (A beta) deposition is a hallmark to define Alzheimer's disease (AD). We investigated the positive rate of brain amyloid deposition assessed with C-11-Pittsburgh compound (PiB)-PET and blood A beta levels in a cohort of probable AD patients who were diagnosed according to the 1984 NINCDS-ADRDA criteria. Eighty-four subjects with a clinical diagnosis of probable AD dementia, amnestic mild cognitive impairment (MCI), and cognitively normal (CN) status were subjected to PiB-PET and F-18-fluorodeoxyglucose (FDG)-PET scans. Plasma biomarkers of A beta(42), A beta(40), and T-tau were measured using single molecule array technology. The positive rate of PiB-PET, the associations between PiB-PET status and FDG-PET, plasma biomarkers, and clinical manifestations were analyzed. PiB-PET was positive in 77.36% of probable AD patients, 31.80% of MCI patients, and 0 of NC. Plasma A beta(42)/A beta(40) ratio was associated with PiB-PET, the ROC curve analysis revealing an AUC of 0.77 (95% CI: 0.66-0.87), with a sensitivity of 82% and specificity of 64%. Some clinical manifestations were associated with PiB-PET imaging. Our findings indicate that only three-fourths of patients diagnosed with probable AD fit the pathological criteria, suggesting that we should be cautious regarding the accuracy of AD diagnosis when no biomarker evidence is available in our clinical practice.