Mucus Plugs in COPD Are Heterogeneous in Size and Shape and Occur in Relatively Large Airways

Abstract BACKGROUND Mucus plugs occur in chronic obstructive pulmonary disease (COPD), but little is known about their size and airway location or whether these mucus plug features change as emphysema worsens. METHODS CT lung scans from 31 participants with COPD from the Subpopulations and Intermediate Outcomes in COPD Study (SPIROMICS) cohort were analyzed to quantify mucus plug size and airway location and extent of emphysema. Radiologist annotations of mucus plugs were incorporated in an image processing pipeline to generate size and location information. Emphysema was quantified as the percentage of voxels less than −950 Hounsfield units. RESULTS The length distribution of 563 annotated mucus plugs varied from 2 to 50 mm. The distribution was multimodal, and an 11 mm length defined short (“stubby”, ≤11 mm) and long (“stringy”, 11 mm) plug phenotypes with stubby plugs being most common (64%). Mucus plugs localized predominantly to airway generations 6 to 9, and their prevalence was highest in in lower lobes. On a lobar basis, the mucus plug number decreased as emphysema % increased whereas average mucus plug volume tended to increase. CONCLUSION COPD is characterized by mucus plugs of varying size and shape and emphysematous lung regions may be differentially susceptible to formation of these plugs. The location of mucus plugs in segmental and subsegmental airways in COPD makes them amenable to treatment with inhaled medications or bronchoscopy.