Longitudinal progression of parenchymal changes on CT images — also referred to as quantitative interstitial abnormalities (QIA) – is independently associated with decreased lung function and an increased all-cause mortality risk, an analysis of two cohorts of ever-smokers indicates. And among the main risk factors for QIA progression is smoking.
“These abnormalities have gone by a few different names but fundamentally, they are high density findings of chest CT that in some cases represent early or subtle evidence of pulmonary fibrosis,” Samuel Ash, MD, MPH, assistant professor of medicine, Brigham and Women’s Hospital, Boston, told this news organization.
So when I see someone with visual evidence of this type of change on their chest CT, I make sure to emphasize that while they don’t have interstitial lung disease [ILD] yet, these findings suggest they may be susceptible to lung injury from tobacco smoke and that if they don’t stop smoking now, they are at risk for a disease like interstitial pulmonary fibrosis [IPF] which is a highly morbid disease with a high mortality risk,” he added.
The study was
Analysis of QIA progression on CT chest scans was carried out on participants from the Genetic Epidemiology of COPD (COPDGene) study as well as those from the Pittsburgh Lung Screening Study (PLuSS). COPDGene was a prospective cohort of over 10,300 ever-smokers with at least a 10–pack-year smoking history between the ages of 45 and 80. Participants underwent a series of tests including chest CT scans at baseline between 2006 and 2011 and again approximately 5 years later.
Patients with a postbronchodilator forced expiratory volume in 1 second (FEV1) of 80% or more of predicted and a FEV1-to-FVC (forced vital capacity) ratio of at least 0.7 were defined to have GOLD stage 0 disease while those with a postbronchodilator FEV1 of 80% or less than predicted and a FEV1-to-FVC ratio of at least 0.7 were defined to have preserved ratio impaired spirometry (PRISm) disease.
PLuSS involved 3,642 ever-smokers between the ages of 50 years and 79 years with at least a 12.5–pack-year history with no prior history of lung cancer. Participants again underwent a series of tests including a CT scan on visit 1 between 2002 and 2005 and then a second CT scan at a second visit almost 9 years later. “In the COPDGene cohort, 4,635 participants had complete clinical data, CT scans and spirometry from visits 1 and 2 for analysis,” the authors reported.
At visit 1 almost 48% of participants were current smokers and the mean pack-year history of the cohort was 41.9 years. The mean time between visits 1 and 2 was 5.6 years. Both the mean prebronchodilator FEV1 as well as the mean FVC decreased between visits 1 and 2. For example, the mean prebronchodilator FEV1 dropped from 2.2 liters to 2.0 liters between visits 1 and 2 while the mean prebronchodilator FVC decreased from 3.2 liters to 3.0 liters between the first and second visits.
In the PLuSS cohort, 1,307 participants had complete imaging and spirometry data available for visits 1 and 2 for analysis. The mean time between visits 1 and 2 was 8.6 years. Over 59% of the cohort were current smokers with a mean pack-year history of 65. Again, the mean prebronchodilator FEV1 and FVC both dropped between visit 1 and 2, as the authors note.
The mean prebronchodilator FEV1, for example, decreased from 2.5 liters to 2.1 liters between visits 1 and 2 while the mean prebronchodilator FVC dropped from 3.6 liters to 3.2 liters during the same interval. Looking at risk factors associated with QIA progression, investigators note that each additional year of baseline age was associated with a higher annual increase in QIA by 0.01% per year (95% confidence interval, 0.01%-0.02%; P < .001) in the COPDGene cohort and a 0.02% increase (95% CI, 0.01%-0.02%; P < .001) in the PLuSS cohort.
Female sex in turn was associated with a 0.07% per year (95% CI, 0.02%-0.12%; P = .003) higher increase in the QIA, compared with men in the COPDGene cohort and a 0.14% (95% CI, 0.02%-0.26%; P = .025) per year higher increase in the QIA in the PLuSS cohort. Current smoking status was only associated with a higher rate of QIA progression in the COPDGene cohort at a rate of 0.10% per year (95% CI, 0.06%-0.15%; P < .001).
Lastly, every copy of the minor allele of the MUIC5B promoter polymorphism was associated with a 0.12% per year (95% CI, 0.07%-0.16%; P < .0001) increase in QIA in the COPDGene cohort as well.