Amyloid-related imaging abnormalities in Japanese patients with Alzheimer's disease treated with Lecanemab: A real-world study.

BACKGROUND: Although clinical trials have suggested a lower incidence of adverse events associated with Lecanemab in Asian populations compared to global cohorts, longitudinal real-world data across broader clinical indications are necessary to confirm these findings in routine practice. OBJECTIVES: This study aimed to provide real-world evidence regarding the safety profile of Lecanemab in Japanese patients in a clinical setting. DESIGN: A real-world observational study with a follow-up period of up to 18 months. SETTING: A single center in Japan. PARTICIPANTS: We included 120 Japanese patients who received Lecanemab between December 2023 and November 2025 and underwent at least one brain MRI before the fifth infusion. MEASUREMENTS: Safety outcomes included amyloid-related imaging abnormalities (ARIA), infusion-related reactions (IRRs), and treatment discontinuation. RESULTS: The mean age was 74.2 ± 7.9 years, and 89 (74%) were female. The majority of patients (88%) had a baseline CDR global score of 0.5. During follow-up, 81 patients completed the 12-month assessment. ARIA occurred in 24 patients (20%); ARIA-E with or without ARIA-H occurred in 5 patients (4%), and isolated ARIA-H occurred in 19 patients (16%). Crucially, no patients experienced symptomatic ARIA. All patients with ARIA-E who had available APOE data were ε4 carriers. Patients with ARIA had significantly lower baseline MMSE scores (p = 0.04), alongside non-significant trends toward higher plasma GFAP levels (p = 0.11) and higher deep white matter Fazekas scores (p = 0.05). IRRs occurred in 34 patients (28%), all of which were mild. Treatment was discontinued in 19 patients (16%), mainly due to disease progression (n = 8). CONCLUSION: In this Japanese AD cohort, Lecanemab demonstrated a manageable safety profile in a real-world setting. In exploratory analyses, potential trends toward a higher frequency of ARIA were observed in patients with lower MMSE scores, higher plasma GFAP levels, and higher Fazekas scores, underscoring the importance of individualized risk assessment prior to therapy.