Amyloid Positron Emission Tomography Imaging at the Onset of Amyloid-Related Abnormalities With Edema in an Alzheimer's Disease Patient.

Amyloid-related imaging abnormalities with edema (ARIA-E) are known adverse events of anti-amyloid monoclonal antibody therapy for Alzheimer's disease (AD), but to our knowledge, amyloid positron emission tomography (PET) captured exactly at the moment of ARIA-E onset has not previously been reported. We report an 85-year-old woman with AD who received anti-amyloid antibody therapy for approximately one year. As part of routine post-treatment evaluation, a second amyloid PET scan obtained 16 days after her final infusion unexpectedly revealed asymptomatic ARIA-E when followed immediately by magnetic resonance imaging (MRI). Compared with the baseline, the follow-up PET showed a marked overall reduction in cortical amyloid burden, including near-complete loss of tracer uptake in the region corresponding to ARIA-E, while the adjacent white matter exhibited reduced, non-specific uptake likely related to edema. This unique, same-day PET-MRI pairing at the moment of ARIA-E detection highlights dynamic regional changes in amyloid signal during treatment and emphasizes the value of continued neuroimaging surveillance even in asymptomatic patients.