Allergic Rhinitis Duration and Small-Airway Dysfunction in Adolescents Without Asthma: A Cross-Sectional Impulse Oscillometry Study.

OBJECTIVE: Allergic rhinitis (AR) is a mucosal inflammatory disease increasingly viewed within a united-airway framework, yet whether lower-airway function deteriorates as AR persists in adolescents without asthma remains unclear. We used impulse oscillometry (IOS) to examine the relationship between AR duration and small-airway function, and examined serum endocan (endothelial cell-specific molecule-1), whose relationship to airway function in AR is unknown, as a candidate systemic biomarker. METHODS: Forty treatment-naïve, aeroallergen-sensitized adolescents (12-17 years) with AR and 37 non-atopic controls of comparable age and sex underwent IOS, serum endocan measurement (ELISA), specific IgE testing, and skin prick testing. Symptoms were scored on a visual analog scale, and core IOS indices were expressed as age- and sex-adjusted z-scores. RESULTS: No IOS parameter differed between patients and controls. However, longer AR duration was associated with higher total-airway resistance (zR5: r = 0.323, p = 0.042) and lower reactance (zX5: r= -0.502, p < 0.001); specific IgE also increased with age, duration, and severity. Serum endocan levels were similar in patients and controls (median 200.8 vs 218.8 ng/mL; p = 0.517) and, within the AR group, did not correlate with severity, persistence, or IOS parameters. CONCLUSIONS: Greater oscillometric small-airway dysfunction was associated with longer AR duration, supporting the use of IOS to assess lower-airway function in adolescents with long-standing AR. Serum endocan did not distinguish patients from controls; because paired airway sampling was not performed, whether any endocan signal in AR is confined to the airway mucosa remains speculative.