This real-world study evaluated the long-term feasibility of lecanemab treatment in 117 patients with early Alzheimer's disease at Kanazawa University Hospital. To assess treatment persistence over a full 18-month course, we focused on the 64 patients who initiated treatment between January and December 2024. Of these 64 patients, 78.1% completed the full 18-month course, and all 48 eligible patients elected to continue beyond 18 months. The overall discontinuation rate was 21.9%, with amyloid-related imaging abnormalities (ARIA) (27.7%), decreased motivation (22.2%), and cognitive decline (11.1%) as the primary reasons. Among all 117 patients, ARIA occurred in 12.9% and was significantly associated with apolipoprotein Eε4 carrier status, elevated baseline cerebrospinal fluid (CSF)-phosphorylated tau (ptau) 181 (ptau181; ≥78.6 pg/ml), ≥2 microbleeds, and Fazekas score≥2 deep white matter hyperintensity. Elevated CSF-ptau181 also independently predicted cognitive decline during treatment and ARIA-related discontinuation. These findings suggest that integrating CSF-ptau181 measurement and baseline MRI into clinical decision-making may support individualized risk stratification and the safe, sustained use of lecanemab in real-world practice.