Assessment of Airway Remodeling Using Endobronchial Ultrasound in Asthma-COPD Overlap

The aim of this study was to evaluate the structural changes of the airways using the endobronchial ultrasound (EBUS) in ACO patients compared to severe asthma and COPD patients.

The study included 17 patients with ACO, 17 patients with COPD and 33 patients with severe asthma. Detailed clinical data were obtained from all participants. Basic laboratory tests were performed, including measurement of eosinophil counts in blood and serum immunoglobulin E (IgE) concentrations. All patients underwent spirometry and bronchoscopy with EBUS (a 20‑MHz ultrasound probe) to measure the total thicknesses of the bronchial walls and their particular layers in segmental bronchi of the right lower lobe. EBUS allows to distinguish five layers of the bronchial wall. Layer 1 (L₁) and layer 2 (L₂) were analyzed separately, while the outer layers (layers 3-5 [L_3-5]) that correspond to cartilage were assessed together.

In patients with ACO the thicknesses of the L₁ and L₂ layers, which are mainly responsible for remodeling, were significantly greater than in patients with COPD and significantly smaller than in patients with severe asthma (median L₁= 0.17 mm vs 0.16 mm vs 0.18 mm, p<0.001; median L₂= 0.18 mm vs 0.17 mm vs 0.20 mm, p<0.001, respectively). The thicknesses of the total bronchial walls (L₁+L₂+L_3-5) and L_3-5 were significantly smaller in ACO and COPD patients compared to asthma patients (median L₁+L₂+L_3-5= 1.2 mm vs 1.14 mm vs 1.31 mm, p<0.001; median L_3-5= 0.85 mm vs, 0.81 mm vs 0.92 mm, p=0.001, respectively).

The process of structural changes in the airways assessed by EBUS is more advanced in individuals with ACO compared to patients with COPD, and less pronounced compared to patients with severe asthma. It seems that EBUS may provide useful information about differences in airway remodeling between ACO, COPD and severe asthma.