Bronchial Wall Thickness in Asthma Linked to Polyps, Exacerbations, Oscillometry

Increased bronchial wall thickness in patients with moderate/severe asthma is associated with severe exacerbations, nasal polyposis, and peripheral airways resistance and reactance, according to study findings published in The Journal of Allergy and Clinical Immunology: In Practice.

Recent research has shown that patients with more severe asthma have increased bronchial wall thickness and worse spirometry results. Investigators therefore sought to characterize clinical associations with bronchial wall thickness in moderate-to-severe asthma.

The researchers initiated a retrospective cohort study of 92 patients with moderate and severe asthma as defined by the Global Initiative for Asthma. Exclusion criteria included patients with chronic obstructive pulmonary disease or bronchiectasis. Among patients with moderate asthma (n=20; mean age 52 years; 70% women), there were 5% who currently smoked, 20% who previously smoked, and 20% with nasal polyps (as measured by endoscopy by the Meltzer system, in which the maximum score is 8). In these patients, mean airway resistance, as measured by the R5-R20 ratio, was 22.6%; mean asthma control level, as measured by the area under the reactance curve (AX), was 0.64; and the mean annual exacerbation rate was 0.0.  Among patients with severe asthma (n=72; mean age 50 years; 71% women) there were 10% who currently smoked, 26% who previously smoked, and 22% with nasal polyps. Among these patients, the mean R5-R20 ratio was 26.6%, mean AX was 1.17, and the mean annual exacerbation rate was 2.5 per year.

For all patients, airway lumen and total airway area at 4 bronchopulmonary segments (right apical; right lower lobe posterior basal; left apico posterior, and left lower lobe posterior basal) was independently determined using high-resolution computed tomography (CT) imaging by thoracic radiologists blinded to clinical data. The researchers then calculated adjusted odds ratios (aORs) for the associations between bronchial wall area thickening (WA≥50%) and:

• forced expiratory volume in 1 second (FEV₁) <80%;
• R5-R20 ratio ≥25% (an oscillometry indicator of peripheral airways disease),
• AX ≥1.0kPa/L (an oscillometry indicator of worse disease control and higher frequency of severe exacerbations),
• severe exacerbations (ie, those requiring oral corticosteroids),
• asthma control questionnaire [ACQ] score ≥1.5, and
• nasal polyps scores.

In pooled analysis of the bronchopulmonary segments, investigators found that bronchial wall thickness was associated with AX of 1.0kPa/L or greater (aOR, 3.54; 95% CI, 1.22-10.32), R5-R20 ratio of 25% or greater (aOR, 2.89; 95% CI, 1.03-8.05), at least 2 exacerbations per year (aOR, 4.17; 95% CI, 1.25-13.90), and nasal polyposis (aOR, 9.85; 95% CI, 2.33-41.74). The increased likelihood for wall area thickening of at least 50% was 72% for those with AX of 1.0kPa/L or greater, 65% for those with R5-R20 ratio of 25% or greater, 76% for those with at least 2 exacerbations per year, and 90% for those with nasal polyposis.

The investigators noted AX had sensitivity (58%) and specificity (66%) for predicting wall area thickening of at least 50% according to receiver operator characteristic curve analysis (area under the curve, 0.64; P =.02). The same analysis showed the R5-R20 ratio of at least 25% had sensitivity of 54% and specificity of 69% (area under the curve, 0.62; P =.06). These findings suggest that oscillometry may be a more sensitive tool for detecting airway remodeling than spirometry, “especially in patients with more severe asthma where there is less disease heterogeneity,” said study authors.

Study limitations include the retrospective design, underpowered sample size, potential change over time in data collection, use of a surrogate measurement for distal airways, and the exclusion of patients with bronchiectasis.

“In the present study we have demonstrated for the first time that peripheral airways resistance and reactance, measured by resistance heterogeneity ratio (R5-R20 divided by R5) and reactance area (AX) respectively, is associated with increased bronchial wall thickness. Additionally, the presence of nasal polyposis and more frequent severe exacerbations requiring OCS are associated with greater bronchial wall thickness measurements,” study authors concluded.

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