Symptomatic lobar intracerebral hemorrhage during extended lecanemab treatment: A case report

Lecanemab is an anti-amyloid-β protofibril antibody that slows cognitive decline in early Alzheimer's disease. Although amyloid-related imaging abnormalities (ARIA) occur predominantly early in treatment, reports of hemorrhagic events during extended treatment beyond 18 months remain limited. A 77-year-old woman completed a standard 1.5-year lecanemab regimen without ARIA on surveillance MRIs. The day after her 42nd infusion, she acutely developed confusion and incomprehensible speech. MRI revealed a 2.5-cm left parietal subcortical hemorrhage. This case highlights that symptomatic lobar hemorrhage may occur even during extended lecanemab therapy, underscoring the importance of continued safety monitoring during extended treatment.