Nearly 40% of patients with chronic obstructive pulmonary disease (COPD), who are current or former smokers but who do not have the characteristic mucus-related symptoms such as cough, phlegm, have silent airway mucus plugs detected on computed tomography (CT) scan, according to a study published in the journal Chest.¹

This study focused on assessing the risk and protective factors as well as the implications of silent airway mucus plugs in patients with clinically diagnosed COPD. Participants from the multicenter COPDGene cohort formed the study group. Chest CT scans were used to quantify the number of pulmonary segments with mucus plugs and calculate the mucus plug score ranging from 0 to 18. Based on the score, the participants were categorized into three groups (0, 1–2, ≥3). Multivariable linear and logistic regression models were used to assess the risk and protective factors for silent mucus plugs and their associations with disease severity.

The total number of participants in the study was 4363. A subgroup of 1739 patients did not have cough or phlegm; of these, 627 (36%) were found to have mucus plugs on CT. Older patients (OR, 1.02) and female patients (OR 1.40) were at higher risk of silent mucus plugs than those who had symptomatic mucus plugs. The risk was also higher among Black patients (OR, 1.93). After adjusting for potential confounders such as age, body mass index, and smoking status, the presence of silent mucus plugs among individuals without cough or phlegm (compared to their absence) was independently associated with worse clinical outcomes, which included a shorter 6-minute walk distance, lower resting arterial oxygen saturation, decreased FEV₁ % predicted, a greater extent of emphysema, increased airway wall thickness, and greater odds of experiencing a severe exacerbation within the past year.

This study has demonstrated a significant association between mucus plugging and poorer functional, structural, and clinical outcomes, suggesting their potential role in disease severity. Mucus plugging is more a consequence of impaired mucus clearance than hypersecretion. Hence, CT scan for mucus plugs should be a part of routine evaluation of COPD patients. The authors suggest that “airway mucus plugging may be a distinct phenotype of COPD and could be an imaging biomarker”. Detection of mucus plugs in asymptomatic COPD patients warrants careful evaluation and management, as their presence is indicative of more severe disease and worse prognosis.

Reference

1.   Mettler SK, et al. Silent airway mucus plugs in COPD and clinical implications. Chest. 2024 Nov;166(5):1010-1019. doi: 10.1016/j.chest.2023.11.033.