E. S. van Etten

Background and purpose Patients who underwent red blood cell (RBC) transfusion from donors who later developed multiple spontaneous intracerebral hemorrhages (ICHs) have recently been identified to have increased risk of ICH themselves. This increased risk of ICH was hypothesized to be related to iatrogenic cerebral amyloid angiopathy (iCAA) transmission. Two cases are presented who had RBC transfusion as an infant and presented with CAA at a relatively young age decades later. Method Cases were identified by prospectively asking all patients at our CAA outpatient clinic (November 2023 to January 2024) about a medical history with RBC transfusion or history with a high likelihood for RBC transfusion (e.g., hemolytic disease, trauma with massive hemorrhage). Eligible patients were all diagnosed with CAA, CAA with concomitant hypertensive arteriopathy or iCAA, and without hereditary CAA. Results Between November 2023 and January 2024, 2/35 (6%, 95% confidence interval 2%–19%) outpatient clinic patients had a history of RBC transfusion and none had a high likelihood medical history. The cases presented at age 47 and 57 and had already developed severe CAA. Conclusions Red blood cell transfusion might be a possible mechanism for iCAA; however, further prospective data collection and experimental evidence concerning blood transmission of amyloid‐β are needed.