Parasitic Infections as Reversible Hyper-IgE Phenocopies in Children with Markedly Elevated IgE: A Retrospective...

Background/Objectives: We aimed to evaluate the etiologic distribution of markedly elevated IgE (≥2000 IU/mL) and the association of parasitic infections with longitudinal IgE dynamics and National Institutes of Health Hyper-IgE Syndrome (NIH-HIES) score trajectories in pediatric patients. Methods: We retrospectively enrolled 127 pediatric patients with IgE ≥2000 IU/mL and ≥1 year of longitudinal follow-up at a tertiary allergy clinic (2019-2024). The primary outcome was the IgE reduction percentage difference between parasitic and non-parasitic groups. Results: Atopic sensitization was identified in 81.0% of tested patients; genetic evaluation was performed in 40 patients (31.5%), with confirmed IEI in one patient (0.8% of the cohort; 2.5% of those evaluated). Parasitic infections were present in 24.4% of patients (n = 31; intestinal parasites 15.7%, scabies 8.7%, hydatid cyst 1.6%; two patients had concurrent intestinal parasitosis and scabies). Median IgE reduction was 63.8% vs. 27.0% in parasitic versus non-parasitic groups (p < 0.001), persisting after multivariable adjustment (p < 0.001). Parasitic infection independently predicted IgE normalization below 2000 IU/mL (OR = 8.26; 95% CI: 2.76-24.68; p < 0.001). All three NIH-HIES inflammatory components (IgE, eosinophilia, eczema) regressed more often in the parasitic group (all p ≤ 0.01); no patient reached the ≥40-point HIES threshold. Conclusions: Parasitic infections produce a clinical phenotype overlapping with hyper-IgE syndrome, constituting a reversible phenocopy of primary immune dysregulation. In populations with substantial parasitic prevalence, parasitological evaluation may be a useful consideration in children with markedly elevated IgE and indeterminate clinical scores; however, this approach should complement rather than replace comprehensive clinical assessment.