WHAT HAPPENS WHEN TWO AD AMYLOID BIOMARKERS HAVE DISCORDANT RESULTS IN THE SAME PATIENT?

Abstract

Due to the development of new diagnostic tools for Alzheimer disease (AD), new clinical scenarios could be found. AD biomarkers increase diagnostic certainty and the risk of having AD. Therefore, they are used for the selection of participants in prodromal AD clinical protocols, but also in the clinical setting to differentiate overlapping dementia syndromes. However, what happens when two AD biomarkers have discordant results in the same patient? The objective of this study is to assess discordant rates between AD (Alzheimer Disease) biomarkers and to analyze longitudinal follow-up of these patients. In our Memory Center, we studied 144 patients with both PET-PiB and Aβ42 values in CSF. We established the percentage of agreement between biomarkers comparing the cut-off of Aβ42 values in CSF and the PET-PIB results. We reviewed the clinical records of patients with discordant results taking into account changes in diagnosis and dementia conversion rate. The percentage of discordance in patients seen in our clinic was 13.8 % (20/144). When we considered only the group of probable AD patients, the rate was only 5.5%. The discordance was due mainly to Aβ42 positive with PET-PIB negative (80%). We excluded 9 patients due to lack of prospective clinical follow up in our center. The clinical diagnosis of these 11 patients were: MCI or probable AD in only 2 cases. The clinical diagnosis for the rest of the cases was heterogeneous and included FTD spectrum, encephalitis and psychiatric diseases. The clinical diagnosis after the medical team received the results was changed in only 4 cases. 4 patients converted to dementia in longitudinal follow up. Discordance between CSF and nuclear methods is more frequent when we evaluated patients with low clinical suspicious for AD. This discordance could be due in part to different sensitivity of the 2 methods but also could reflect a more heterogeneous non AD population.