A110-09 Small Airway Disease in Interstitial Lung Disease Is Common and Correlates With Disease Severity

Rationale Detection of small airway disease (SAD) using impulse oscillometry (IOS) has clinical value in airway disorders, but its role in interstitial lung diseases (ILD) is not well defined. We aimed to assess the prevalence of SAD and its clinical correlations in patients with ILD. Methods We conducted a prospective registry-based observational study including patients with a multidisciplinary diagnosis of ILD who underwent IOS, pulmonary function tests, and six-minute walking test (6MWT). SAD was defined as either frequency dependence of resistance (R5-20) >0.1 kPa/L/s or an area under the reactance curve (AX) >1.0 kPa/L. Results Nighty-four patients (median age 70y; 44% females) completed all evaluations and were included. The most common ILD were connective tissue disease-related ILD (32%) and hypersensitivity pneumonitis (22%), with 74% of patients demonstrating fibrotic disease. SAD was identified in 46 patients (49%) and was not associated with any baseline characteristic, fibrosis, or ILD subtype. However, SAD was linked to lower forced vital capacity (median 74% vs. 84% predicted, p < 0.01), total lung capacity (75% vs. 86% predicted, p = 0.04), and diffusing capacity for carbon monoxide (48% vs. 54% predicted, p = 0.02). Patients with SAD also had reduced exercise capacity (median 6MWT 413 vs. 465 meters, p = 0.01). Among fibrotic ILD, more patients with SAD met the definition of progressive pulmonary fibrosis in the year prior to inclusion (60% vs. 18%, p < 0.001), with higher rates of DLCOc decline, and radiologic and symptoms worsening (Figure 1). Maximal mid-expiratory flows did not show the above correlations. AX and R5-20 were higher in patients with air-trapping or mosaic attenuation in chest CT, but were not associated with honeycombing or traction bronchiectasis. Conclusion SAD is common in ILD and correlates with worse disease severity independent of patient characteristics.