Lecanemab treatment modulates brain volume and cerebrospinal fluid pathways in early Alzheimer's disease: Insights from longitudinal magnetic resonance imaging

INTRODUCTION Lecanemab provides clinical benefits in early Alzheimer's disease (AD), but its longitudinal effects on brain structure, particularly cerebrospinal fluid (CSF) compartments, remain unclear. This study examined treatment‐associated structural changes using longitudinal MRI. METHODS Thirty‐one patients with mild cognitive impairment (MCI) or early AD underwent baseline and follow‐up (1–7 months) 3D T1‐weighted MRI during lecanemab treatment. Gray matter (GM), ventricular, choroid plexus (CP), and perivascular space (PVS) volumes were quantified. Longitudinal changes were analyzed with paired tests and linear mixed‐effects models (LMMs). RESULTS Significant GM volume reductions were observed in AD‐vulnerable regions (hippocampus, entorhinal cortex, precuneus), with increased CSF volumes. PVS volume showed a modest, non‐significant decline. CP enlargement was associated with ventricular expansion. DISCUSSION Lecanemab treatment was associated with coordinated parenchymal and CSF‐related structural changes. CP and PVS dynamics may represent potential MRI‐based markers for monitoring early AD.