Findings on Thoracic Computed Tomography Scans and Respiratory Outcomes in Persons with and without Chronic Obstructive Pulmonary Disease: A Population-Based Cohort Study

Abstract

Background: Thoracic computed tomography (CT) scans are widely performed in clinical practice, often leading to detection of airway or parenchymal abnormalities in asymptomatic or minimally symptomatic individuals. However, clinical relevance of CT abnormalities is uncertain in the general population.

Methods: We evaluated data from 1361 participants aged ≥40 years from a Canadian prospective cohort comprising 408 healthy never-smokers, 502 healthy ever-smokers, and 451 individuals with spirometric evidence of chronic obstructive pulmonary disease (COPD) who had thoracic CT scans. CT images of subjects were visually scored for respiratory bronchiolitis(RB), emphysema(E), bronchial-wall thickening(BWT), expiratory air-trapping(AT), and bronchiectasis(B). Multivariable logistic regression models were used to assess associations of CT features with respiratory symptoms, dyspnea, health status as determined by COPD assessment test, and risk of clinically significant exacerbations during 12 months follow-up.

Results: About 11% of life-time never-smokers demonstrated emphysema on CT scans. Prevalence increased to 30% among smokers with normal lung function and 36%, 50%, and 57% among individuals with mild, moderate or severe/very severe COPD, respectively. Presence of emphysema on CT was associated with chronic cough (OR,2.11; 95%CI,1.4-3.18); chronic phlegm production (OR,1.87; 95% CI,1.27-2.76); wheeze (OR,1.61; 95% CI,1.05-2.48); dyspnoea (OR,2.90; 95% CI,1.41-5.98); CAT score≥10(OR,2.17; 95%CI,1.42-3.30) and risk of ≥2 exacerbations over 12 months (OR,2.17; 95% CI, 1.42-3.0).

Conclusions: Burden of thoracic CT abnormalities is high among Canadians ≥40 years of age, including never-smokers and smokers with normal lung function. Detection of emphysema on CT scans is associated with pulmonary symptoms and increased risk of exacerbations, independent of smoking or lung function.

Fig 1. Prevalence of respiratory bronchiolitis; air-trapping; bronchial wall thickening; emphysema; bronchiectasis.

Five study subgroups are: Normal (FEV₁/FVC ≥ LLN and never smoker); At Risk (FEV₁/FVC ≥ LLN and ever smoker); Mild COPD (FEV₁/FVC < LLN and FEV₁%Pred ≥ 80%); Moderate COPD (FEV₁/FVC < LLN and 50% ≤ FEV₁%Pred < 80%); Severe to very severe COPD (FEV₁/FVC < LLN and FEV₁%Pred < 50%). All P values are corrected by Holm-Bonferroni correction for multiple comparisons. P values<0.05: *ref = Normal; # Ref = At Risk; ϕ Ref = LLN Mild; θ Ref = LLN moderate.

Fig 2. The relationship of bronchiolitis, Bronchiectasis, bronchial wall thickening, and emphysema with six Patient-Reported Outcomes.

The outcomes are: chronic cough; chronic phlegm; wheezing; dyspnea [mMRC scale ≥2]; COPD assessment test [CAT] score>10; and exacerbation ≥2 in 1 year follow-up). The Odds Ratio (aOR [95% CI]) were adjusted for age, sex, BMI, Pack-years, and FEV1. * p value <0.05.