TITLE : "Tissue Eosinophil Counts as Predictors of Infliximab Response in Pediatric Inflammatory Bowel Disease: A Retrospective Nested Case Control Study"

BackgroundInfliximab is an effective therapy for pediatric inflammatory bowel disease (IBD), but a substantial proportion of patients experience primary non-response or relapse. Tissue eosinophilia has been implicated in treatment resistance, yet its predictive value in pediatric populations remains unclear. MethodsWe conducted a retrospective nested case-control study including 80 pediatric IBD patients treated with infliximab at CHU Sainte-Justine between 2014 and 2023 Relapse cases (n = 42) were defined by an increase in the short Pediatric Crohns Disease Activity Index (sPCDAI) [≥]10, and compared with non-relapse controls (n = 38). Tissue eosinophil counts were quantified from diagnostic biopsies by blinded reviewers. Primary non-response was defined as a lack of clinical improvement before treatment change. Logistic regression and receiver operating characteristic (ROC) analyses were performed to assess associations between eosinophil counts and treatment outcomes. Results80 patients were included in the study. Median age at diagnosis was 14.4 years (interquarile range [IQR] 3.65). Forty patients had a diagnosis of ulcerative colitis (UC, 50%) and the other half had a diagnosis of Crohns disease (CD). Baseline eosinophil counts were not associated with subsequent relapse (odds ratio [OR] 1.02, 95% CI 0.98-1.06, p = 0.31), and ROC analysis demonstrated poor discrimination (AUC 0.57). In contrast, higher eosinophil counts were associated with primary non-response in ulcerative colitis patients (OR 1.08, 95% CI 1.01-1.16, p = 0.03). A cutoff of a median of [≥] 36 eosinophils per high-power field among all segments yielded 85% sensitivity and 80% specificity for predicting primary non-response (AUC 0.82). ConclusionTissue eosinophil counts do not predict relapse in pediatric IBD patients treated with infliximab. However, elevated counts may identify ulcerative colitis patients at risk of primary non-response, suggesting a role for histological stratification in guiding the selection of biologics. Prospective validation in larger cohorts is warranted.