Early inhaled corticosteroid reduction as a dynamic indicator of treatment response in children receiving house dust mite subcutaneous immunotherapy

Background: Clinical response to house dust mite subcutaneous immunotherapy (HDM-SCIT) in children is heterogeneous. Existing prediction approaches rely mainly on baseline characteristics and do not capture early treatment-related change. Objective: To evaluate whether early change in inhaled corticosteroid use within 3 months (ΔICS) provides additional predictive information beyond baseline characteristics for HDM-SCIT response stratification. Methods: Two ordinal regression models were developed. The base model included age, sex, baseline ICS dose (ICS0), FEV1baseline, eosinophils, FeNOcat25, tIgEbaseline, HDMₘax, and ratioₘax. The extended model additionally included early ICS change at 3 months (ΔICS), scaled per 100 μg/day (ΔICS₁00). Model performance was assessed using AIC, discrimination across four classification tasks, and calibration. Restricted cubic spline analysis was used to examine the association between ΔICS and high-response probability. Results: A total of 470 children were included, including 159 high responders, 151 middle responders, and 160 low responders. Adding ΔICS₁00 significantly improved model fit (AIC 762. 5 ± 3. 3 vs. 871. 2 ± 4. 1; pooled Wald test, P < 0. 001). The extended model showed better discrimination for high versus non-high response (AUC 0. 738 to 0. 878), middle versus non-middle response (0. 613 to 0. 725), low versus non-low response (0. 820 to 0. 842), and high versus low response (0. 856 to 0. 928). Restricted cubic spline analysis demonstrated a significant non-linear association between ΔICS and high-response probability (overall P < 0. 001; non-linearity P < 0. 001), with an inflection region around -80 to -50 μg/day. Conclusion: Early change in inhaled corticosteroid use (ΔICS) may provide additional predictive information beyond baseline variables in children receiving HDM-SCIT. The observed non-linear association suggests that ΔICS may be a useful exploratory early treatment-related indicator, but external validation is required before clinical application.