Effective amyloid clearance with lecanemab in a female with Alzheimer's disease: A case report.

Anti-amyloid monoclonal antibodies, including lecanemab, have been approved for patients with mild cognitive impairment (MCI) or mild dementia due to Alzheimer's disease (AD). Further clarification of the long-term safety and effectiveness of these disease-modifying therapies is essential in patients treated outside the setting of clinical trials. We report an 81-year-old woman with amnestic MCI due to AD who was treated with lecanemab for 18 months in a clinical setting. At baseline, she had mild memory impairment without functional decline (Mini-Mental State Examination-Japanese version [MMSE-J], 29; Clinical Dementia Rating global score [CDR-GS], 0.5), extensive cortical amyloid deposition on ¹¹C-Pittsburgh compound B positron emission tomography (PET; centiloid [CL], 107.1), and elevated cerebrospinal fluid phosphorylated tau 181; she received 36 biweekly intravenous lecanemab (10 mg/kg). During treatment, surveillance magnetic resonance imaging revealed no amyloid-related imaging abnormalities, no adverse events occurred, and cognitive and functional status remained stable at 18 months (MMSE-J 28; CDR-GS 0.5), while amyloid PET demonstrated marked amyloid clearance (CL 21.3). This case illustrates substantial amyloid clearance with preserved cognitive and functional status after 18 months of lecanemab treatment without treatment-related safety concerns. Continued lecanemab therapy beyond 18 months may be feasible in carefully selected patients with early-stage AD, although further real-world data are needed to establish its long-term benefits and risks.