Association Between CT Mucus Plugging and Airway Wall Thickness in COPD and Asthma

Rationale: There is minimal understanding of how mucus plugs manifest in airways, particularly in individuals with asthma or chronic obstructive pulmonary disease (COPD). Recently, a visual computed tomography (CT) scoring system was developed to quantify mucus. 1 High mucus scores on CT have been shown to be associated with worse lung function and ventilation abnormalities, 1 increased sputum eosinophils, 1 FeNO 1 and sputum IL-4 1 in asthma, 2 and predict all-cause mortality in COPD 3 . However, there is limited understanding of the CT airway wall features associated with mucus plugging. Thus, our objective was to determine the relationship between CT airway wall thickness and mucus plug score in spatially matched regions of interest in the lungs in patients with COPD and asthma. Methods: CT imaging was performed in patients with a diagnosis of asthma or COPD at St. Joseph's Healthcare Hamilton (Canada). CT images were scored for mucus plugging using the bronchopulmonary segment-based scoring system 1 by two radiologists with subspeciality interest in Chest Imaging and more than 15 years experience; mucus plugging was defined to occur if either radiologist identified a complete luminal obstruction at the subsegmental level. Quantitative CT analysis was performed using commercial software (VIDA Diagnostics Inc.) to measure Pi10, defined as the wall thickness of a theoretical airway with a lumen perimeter of 10mm. Multivariable logistic regression models were developed to determine the association between mucus plug score (0/1) and Pi10; each of the 19 segments was treated as a nested variable. Age, BMI and disease diagnosis (asthma or COPD) were included in the model as covariates. Results: A total of 36 participants were evaluated; n=17 with COPD and n=19 with asthma. The patients had a mean age=6015 years, BMI=28.97.6 kg/m 2 , FEV 1 =1.490.70 L, FEV 1 /FVC=55.815.2%, and there were 15/21 males/females. A mucus plug was reported in at least one segment for all 36 patients. Multivariable regression analysis showed CT Pi10 was significantly associated with the presence of mucus plugs (=1.995, p=0.01); for every one unit increase in Pi10 the probability of mucus plugging in a segment increased by a factor of 7.35 (95%CI=1.51-35.9). Disease diagnosis (COPD/asthma) was not associated with mucus score (p=0.85). Conclusions: Mucus plugging is associated with thicker airway walls in patients with asthma and COPD.