Mucus Plugging Associated With Airway Wall Thickening in Asthma and COPD

Patients with asthma and chronic obstructive pulmonary disease (COPD) have increased airway wall thickness and reduced airway counts on computed tomography (CT) in segments in which there is a distal mucus plug compared with segments without mucus plugs, according to a study in Respiratory Medicine.

The development of mucus plugs that occur in the airways of those with asthma and COPD and the role of these plugs in disease pathogenesis is not well understood.

Investigators therefore conducted a retrospective analysis assessing the spatial relationships between CT airway measurements and mucus scoring in patients with asthma and COPD. Eligible participants were consecutive patients referred to the complex airways disease clinic at a center in Hamilton, Ontario, Canada, between January and November 2019.

In the study, 2 experienced radiologists and 3 radiology senior trainees scored mucus plugging found in CT images using a bronchopulmonary segment-based scoring system. The subsegmental airways of the 19 airway segments were assessed, with the total mucus score determined by a sum of the score in each segment. Mucus plugging was deemed to have occurred when at least 3 radiologists identified a complete luminal occlusion of at least 1 of the subsegmental airways by mucus.

A total of 33 participants (16 with asthma, 17 with COPD; mean age 60±15 years; 42% male) were included in the analysis. Participants’ mean forced expiratory volume in 1 second (FEV₁) was 53±21% predicted; the mean FEV₁/forced vital capacity was 54±15%; and the mean mucus score was 15 4 (minimum=0, maximum=19).

Significantly increased CT wall-area percentage in airway segments with mucus plugs was observed compared with segments without mucus plugs for LB8 and LB9 (P <.05), as well as significantly reduced CT lumen area in airway segments with mucus plugs vs those without in the LB9 segment (P <.05). Investigators also found a statistically significant correlation between the average segmental CT wall-area percentage and total mucus score (r =0.36, P =.04), with no other significant correlations observed (P >.05).

Mixed effects linear regression assessed the relationship between CT measurements and mucus scores, with each of the 19 segments as a repeated factor. This analysis was adjusted by age, sex, height, and diagnosis of asthma or COPD. A separate analysis was also performed that included each CT measurement. For CT total airway count, a significant main effect for mucus score was observed, suggesting fewer CT airways in segments with a mucus plug than without.

An additional analysis also looked at the relationship between mucus score and CT wall-area percentage. Here, the researchers found a significant main effect, indicating that airways proximal to a mucus plug had thicker airway walls on CT compared with airways without a mucus plug. No significant main effect was found for mucus plugs in the CT lumen area.

In citing study limitations, the investigators noted that because study participants had more severe disease and a relatively high mucus burden, findings might not apply to all patients with asthma or COPD. Also, the study lacked a standardized imaging acquisition protocol.

“We investigated the relationship between CT mucus plugging and airway measurements in vivo in asthma and COPD, and showed that there was increased airway wall thickness and reduced airway counts on CT in segments where there was a distal mucus plug compared to segments without mucus plugs,” the investigators concluded.

Disclosure: Some of the study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.

Reference

Tran C, Veer Singh G, Haider E, et al. Luminal mucus plugs are spatially associated with airway wall thickening in severe COPD and asthma: a single-centered, retrospective, observational study. Respir Med. 2022;202:106982. doi:10.1016/j.rmed.2022.106982