LONDON – Recent evidence of ever smokers having measurable deficits in activity even when lung function is preserved has been further expanded by findings suggesting a different phenotype for patients in this group with radiologic evidence of emphysema, according to data from SPIROMICS (Subpopulations and Intermediate Outcome Measures In COPD Study).
The most recent data were presented at the annual congress of the European Respiratory Society.
Earlier this year, published data drawn from SPIROMICS demonstrated that current and former smokers with preserved lung function (forced expiratory volume in 1 second:forced vital capacity greater than or equal to 0.70) had activity limitations, respiratory symptoms, and exacerbations even though they did not meet the current definition of chronic obstructive pulmonary disease (COPD) (N Engl J Med. 2016;374:1811-21). In the new analysis, further distinctions could be made for patients in this subgroup who also had emphysema on computed tomography (CT).
“Among smokers with preserved lung function, emphysema on CT was associated with reduced activity levels and desaturation on the 6-minute walk test (6MWT),” reported Christian M. Lo Cascio, MD, Columbia University, New York. Compared with smokers with preserved lung function without CT evidence of emphysema, the patients with emphysema on CT did not have more symptoms or exacerbations.
“These and prior findings suggest two distinct but overlapping phenotypes in ever smokers with preserved lung function: an airway disease with respiratory symptoms and frequent exacerbations and emphysema characterized by activity limitation and increased mortality,” said Dr. Lo Cascio.
SPIROMICS, an observational study supported by the National Heart, Lung, and Blood Institute, has enrolled current and former smokers at six centers in the United States to prospectively analyze biomarker, genetic, and clinical data. In the previously published analysis, the focus was on the difference between 849 ever smokers with preserved lung function and 963 patients with mild to moderate COPD. In the data presented by Dr. Lo Cascio, 901 SPIROMICS patients with preserved lung function were analyzed with the focus on the difference between the 66 (7%) who had radiologic evidence of emphysema and the 835 (93%) who had undergone CT indicating that they did not have emphysema.
“Our hypothesis was that the subgroup of patients with emphysema on CT would have lower activity levels, greater desaturation of at least 4% on the 6MWT, more respiratory symptoms, and more exacerbations,” Dr. Lo Cascio reported.
The hypothesis was only half correct. As measured on the activity component of the St. Georges Respiratory Questionnaire, there was about a 10-point (P less than .001) greater reduction in reported activity levels among those with emphysema on CT relative to those without. In addition, the odds ratio (OR) for significant oxygen desaturation, defined as a 4% fall in oxygen saturation of hemoglobin during the 6MWD, was approximately two times greater (P less than .001) for the patients with CT evidence of emphysema.
There were no significant differences between the two groups in walking distance on the 6MWD. Both sets of patients had the same rate of exacerbations and scores on the symptom component of the St. Georges Respiratory Questionnaire, which captures cough, phlegm, wheezing, shortness of breath, and symptom-free days.
Overall, when ever smokers with preserved lung function were subdivided into those with and without CT evidence of emphysema, several similarities were found between the two groups. For those with CT evidence of emphysema and those with no CT evidence of emphysema, mean pack-years of smoking were 43 years and 40 years, respectively, and average body mass indexes were 28.1 and 29.1, respectively. The percentage of patients who had a COPD Assessment Test score of greater than or equal to 10 was 61% among those with CT evidence of emphysema, vs. 50% among those patients without CT evidence of emphysema.
When asked if looking for emphysema on CT in ever smokers with preserved lung function might have clinical utility, Dr. Lo Cascio suggested that it is not yet clear how this information might change management. These data strengthen other evidence from SPIROMICS that ever smokers who do not meet the definition of COPD already have a significant disease burden, he said.
Dr. Lo Cascio reports no relevant financial relationships.