Prognostic impact of onset timing on response to methylprednisolone pulse therapy for idiopathic pneumonia syndrome after allogeneic hematopoietic cell transplantation

Idiopathic pneumonia syndrome (IPS) is a serious complication following allogeneic hematopoietic cell transplantation (HCT), often treated with methylprednisolone (mPSL) pulse therapy. However, treatment responses vary. This study aimed to identify predictors of poor response to mPSL monotherapy. Among 289 patients who underwent allogeneic HCT, 25 developed IPS and received mPSL pulse therapy. Clinical responses were categorized as complete (CCR), partial (PCR), or no response (NR), based on oxygen requirements within 28 days. We compared baseline characteristics of responders (CCR: <i>n</i> = 5; PCR: <i>n</i> = 6) and non-responders (NR: <i>n</i> = 14). Univariate analysis revealed that IPS onset on day +73 or later (<i>p</i> = 0.033), reduced intensity conditioning (<i>p</i> = 0.033), use of total body irradiation (<i>p</i> = 0.049) or fludarabine (<i>p</i> = 0.042), and nonuse of busulfan (<i>p</i> = 0.049) in preparative regimens were associated with poor response. Multivariate analysis identified a longer time from transplantation to IPS onset as a significant predictor of poor response (Odds Ratio 1.017 per 1-day increase; 95% CI 1.007-1.036; <i>p</i> = 0.045). The present study may provide valuable insights into how the responsiveness to mPSL varies depending on the time of IPS onset. Alternative therapeutic strategies may be needed for patients with late-onset IPS.