Nomogram for predicting 6-month BMIZ changes in children with Crohn's disease: a single-center retrospective study

Perianal disease (PD) is an aggressive phenotype in children with Crohn's disease (CD), but its measurable impact on short-term nutritional recovery remains understudied. This study aimed to evaluate the independent effect of PD on the 6-month Body Mass Index Z-score (BMIZ) trajectory and to develop a practical nomogram for early risk stratification in pediatric CD.

A single-center retrospective cohort of 51 pediatric CD patients (29 with PD and 22 without PD) with at least 6 months of follow-up was enrolled from a tertiary hospital in Fujian, southern China, between July 2017 and March 2025. BMIZ trajectories over time were estimated using linear mixed models (LMM). Predictors of 6-month ΔBMIZ were screened using univariate regression (P < 0.20), followed by LASSO regression (tenfold cross-validation) to construct a nomogram. Model performance was internally validated using 1000 bootstrap resamples (R², MAE, RMSE) and calibration plots. Decision curve analysis (DCA) was performed to evaluate clinical utility for predicting inadequate nutritional recovery (ΔBMIZ ≤ 0.40).

LMM analysis showed that PD status significantly reduced the slope of BMIZ recovery after adjusting for age, sex, and biologic therapy (β = -0.085, 95% CI -0.147 to -0.023, P = 0.010). LASSO regression identified six core predictors: perianal disease, positive fecal occult blood test (FOBT), biologic therapy, erythrocyte sedimentation rate (ESR), hemoglobin (Hb), and 25-hydroxyvitamin D3 (25(OH)D3). The nomogram demonstrated satisfactory predictive performance (R² = 0.51, MAE = 0.40, RMSE = 0.49), with calibration plots showing good agreement between predicted and observed ΔBMIZ. DCA confirmed a positive net benefit for predicting inadequate nutritional recovery (ΔBMIZ ≤ 0.40) across a threshold probability range of 5% to 85%.

Perianal disease was independently associated with suboptimal short-term nutritional recovery in children with CD. The proposed nomogram, integrating phenotypic, inflammatory, and nutritional markers, may help identify high-risk patients at diagnosis or early after diagnosis and support individualized nutritional monitoring and therapeutic planning in southern Chinese pediatric CD patients.