Bronchiolitis Obliterans or Busulfan-Induced Lung Injury? A Pediatric Case of Hematopoietic Stem Cell Transplantation

Description of a clinical case regarding a 4-year-old boy with β-thalassemia major developed severe progressive lung disease after haploidentical HSCT. The central challenge was distinguishing between bronchiolitis obliterans (chronic lung GVHD) and busulfan-induced pulmonary toxicity — two conditions with overlapping features — without histological confirmation, as biopsy was too risky. Despite aggressive treatment, the child progressed to end-stage respiratory failure. He ultimately underwent living donor lung transplantation from the same HSCT donor (his father), achieving clinical stability without immunosuppression, likely due to transplant tolerance conferred by full donor chimerism. The case highlights the complexity of multifactorial post-HSCT lung disease in young children and the potential of individualized donor-matched lung transplantation as a rescue strategy.