Real-world implementation of lecanemab in Alzheimer's disease: A Japanese cohort.

INTRODUCTION: Real-world evidence for lecanemab remains limited, particularly among Asian populations. We evaluated the feasibility, safety, biomarker profiles, and short-term clinical outcomes of lecanemab in practice in Japan. METHODS: We screened 321 patients with early Alzheimer's disease (AD) and confirmed amyloid pathology using amyloid positron emission tomography (PET) or cerebrospinal fluid analysis. Plasma amyloid-β42/40 was assessed when available. Among these, 102 initiated lecanemab and underwent structured magnetic resonance imaging (MRI) surveillance with 6 months of follow-up. RESULTS: Most treated patients had a Clinical Dementia Rating-Global (CDR-Global) score of 0.5 (96.1%), and 6-month treatment persistence exceeded 85%. Amyloid-related imaging abnormalities (ARIA), predominantly mild and asymptomatic ARIA-H, occurred in 11.4%, whereas no cases of isolated ARIA with effusion or edema (ARIA-E) were observed. One macrohemorrhagic and two moderate-severe radiographic ARIA with hemorrhage or hemosiderin deposition (ARIA-H) developed, which led to discontinuation of the treatment. Cognitive and functional measures remained generally stable over 6 months, with changes comparable to those reported in the phase 3 CLARITY-AD trial. Plasma-PET discordance highlighted the complementary value of multimodal biomarker interpretation. DISCUSSION: Lecanemab was feasible and generally well tolerated under structured MRI monitoring in routine Japanese practice.