Clinically Silent Amyloid-Related Imaging Abnormality With Edema Following Lecanemab Therapy: A Case Report.

Amyloid-related imaging abnormalities with edema (ARIA-E) are a known complication of anti-amyloid monoclonal antibody therapies such as lecanemab. ARIA-E represents vasogenic cerebral edema resulting from treatment-related disruption of vascular amyloid and appears on MRI as cortical or gyriform T2 fluid-attenuated inversion recovery (FLAIR) hyperintensities. Clinically, ARIA-E ranges from asymptomatic radiologic findings to symptomatic events such as headache, confusion, or seizures, making routine surveillance important during therapy. We present the case of a 60-year-old woman with biomarker-confirmed AD who developed radiographically evident ARIA-E following six biweekly infusions of lecanemab. Surveillance MRI revealed new cortically based and gyriform T2 FLAIR hyperintensities in the posterior occipital and bilateral temporal lobes, consistent with parenchymal and sulcal edema. Notably, the patient remained neurologically asymptomatic throughout the episode. Lecanemab therapy was discontinued, and she was managed conservatively with close outpatient follow-up. This case highlights the importance of routine imaging during anti-amyloid therapy and demonstrates that conservative management may be appropriate in select asymptomatic cases of ARIA-E.