Symptomatic new-onset bronchiectasis after allogeneic haematopoietic stem cell transplantation – revealing an undiagnosed complication

<bold>Introduction:</bold> Bronchiectasis is a known complication in immune-related conditions. However, their prevalence following allogeneic haematopoietic stem cell transplantation (allo-HSCT) is unkown. <bold>Objective:</bold> To evaluate the prevalence, predictors, characteristics, and outcomes of symptomatic new-onset bronchiectasis (SNOBE) after allo-HSCT. <bold>Methods:</bold> Consecutive subjects that underwent allo-HSCT between 2014 and 2022 in a tertiary center. Chest CT scans of subjects with ongoing unexplained respiratory symptoms were analyzed and compared to pre-HSCT scans. Consecutive subjects that visited our clinic with non-HSCT-related bronchiectasis were included as a control group in a ratio of 1:3. <bold>Results:</bold> Overall, 282 subjects underwent allo-HSCT, and 182 (65%) survived without recurrence at 6 months and were included. Of them, 36 (20%) had SNOBE, with 33 (92%) having concurrent chronic graft vs. host disease (cGVHD). Median (IQR) days from HSCT and cGVHD to SNOBE were 304 (202-547) and 80 (31-215), respectively. Among subjects with cGVHD, independent predictors for SNOBE were severe cGVHD (adjusted OR 9.3, 95% 2.3-36), gastrointestinal cGVHD (AOR 3.7, 95% CI 1.3-10), and lower baseline FEV1/FVC (AOR 0.93, 95% CI 0.88-0.99). Compared to the control group, SNOBE had diffuse distribution (44% vs. 13%) and higher FACED scores (median 3 vs. 2). Subjects with SNOBE had lower survival (HR 1.91, 95% CI 1.1-3.6), with 2 exacerbations and 1 respiratory-related hospitalization in the first year. <bold>Conclusion:</bold> SNOBE are prevalent after allo-HSCT, with unique features and major impact. High awareness, low-threshold for imaging, and early pulmonologist involvement are neeed.