Clinical and pathophysiological roles of lower lobe-dominant mucus plugs on computed tomography in patients with asthma with and without bronchiectasis.

BACKGROUND

Despite the clinical relevance of mucus plugging, the role of spatial distribution of mucus plugs remains unclear in patients with asthma.

OBJECTIVE

We sought to examine whether greater lower lobe mucus plug dominance is associated with more clinical and pathophysiological impairments in 2 cohorts, including patients with and without bronchiectasis.

METHODS

Patients with asthma without and with clinical diagnosis of bronchiectasis underwent chest computed tomography at Kyoto University Hospital (Kyoto cohort) and Japanese multicenters (bronchiectasis and asthma [BEXAS] cohort), respectively. Mucus plugs in airways were visually scored on computed tomography, and the difference in mucus plug score between lower and upper-middle lobes (Δ mucus plug score) was calculated.

RESULTS

Among 176 (Kyoto) and 42 (BEXAS) enrolled patients, 82 and 33 exhibited mucus plug scores greater than or equal to 1, respectively. Higher Δ mucus plug score was associated with lower percentage of the predicted FEV1 and the presence of exacerbation history in both cohorts. Higher Δ mucus plug score was associated with luminal narrowing of the fifth-generation, but not the third- or fourth-generation, lower lobe airways in the Kyoto cohort, and bronchiolitis score in the BEXAS cohort. In the multivariable model, higher Δ mucus plug score was associated with symptoms and exacerbations, independent of whole-lung mucus plug score in the Kyoto cohort.

CONCLUSIONS

Lower lobe-dominant mucus plugs were associated with lower lung function and exacerbations in patients with asthma, irrespective of comorbid bronchiectasis. The spatial distribution of mucus plugs additionally to whole-lung mucus plug score may help to understand clinical roles of mucus plugging in asthma.