Introduction
Bronchiolitis obliterans syndrome (BOS) is a life-threatening
complication of allogeneic hematopoietic cell transplant (HSCT)1. It is characterized by an irreversible small airway
obstruction caused by epithelial injury, subepithelial inflammation, and
fibrosis of small airways 2. The prevalence of BOS was
reported 2%-6.5% in allogeneic HSCT recipients in adult cohort3-5, and 2.0-2.7% in pediatric cohorts6,7. The prognosis of children with BOS after HSCT is
poor; the five-year survival rate is 45-59% 8,9.
Since the number of patients receiving allogeneic HSCT is increasing,
BOS in children will likely increase in the future.
A BOS diagnosis is based on declining FEV1, which is
measured serially after HSCT 10, and confirmed with
pathology of constrictive bronchiolitis or high-resolution computed
tomography (CT) showing air trapping, small airway thickening, or
bronchiectasis 11. After BOS diagnosis, pulmonary
functions are measured regularly to monitor treatment efficacy and
prognosis 12. Systemic steroids have been the backbone
of BOS therapy 13-17 and inhaled fluticasone,
azithromycin, and montelukast (FAM) have been recently introduced18. However, the prognosis of BOS is still poor.
A study enlisting subjects with BOS in a multicenter prospective trial
and a retrospective cohort concluded that FEV1 declined
rapidly in the 6 months prior to BOS diagnosis 19. The
current study is one of few studies that describe the longitudinal
change of lung function after BOS diagnosis in children and clarify the
clinical implications of lung function changes on BOS prognosis.