Bronchiectasis after allogeneic hematopoietic cell transplantation - an underdiagnosed complication.

Background: Bronchiectasis (BE) following allogeneic hematopoietic cell transplantation (allo-HCT) are described in the context of bronchiolitis obliterans syndrome (BOS). However, data on its overall prevalence and characteristics in allo-HCT patients are scarce.

Objective: To assess the prevalence, characteristics, and outcomes of symptomatic new-onset bronchiectasis after allo-HCT.

Methods: A prospective database with all subjects that underwent allo-HCT between 2014 and 2022 in a tertiary center was utilized. Chest CT scans of subjects with respiratory symptoms were analyzed and compared to pre-HCT scans for BE. Changes in pulmonary function tests (PFTs) and mortality were compared between patients with and without BE.

Results: Overall, 282 subjects underwent allo-HCT and 182 survived at 6 months. Thirty-six patients (20 %) were diagnosed with new-onset BE. Median (IQR) duration from HCT to BE diagnosis was 304 (202-547) days. Of those with BE and serial PFTs, 39 % met the criteria for BOS. Independent predictors for BE included chronic graft vs. host disease (adjusted OR 6.8, 95 % CI 1.34-34.6) and a lower baseline FEV1 % (aOR 0.95, 95 % CI 0.92-0.98). BE was associated with increased hazard of mortality (HR 1.91, 95 % CI 1.1-3.6), validated by an extended cox model and sub-group analyses. Patients meeting the criteria for BOS had lower follow-up PFTs and a higher rate of diffuse distribution of bronchiectasis (67 % vs. 32 %). Moreover, patients with BOS had increased mortality compared to BE not meeting these criteria (HR 3.40, 95 % CI 1.2-9.4).

Conclusions: Bronchiectasis is prevalent after allo-HCT with major impact, not solely explained by BOS.