Emphysema Threshold on CT Imaging May Have Predictive Value for COPD

Individuals diagnosed with chronic obstructive pulmonary disease (COPD) with ≥5% emphysema based on thoracic computed tomography (CT) imaging may be at greater risk for poor outcomes and may benefit from directed therapy, according to a study published in the American Journal of Respiratory and Critical Care Medicine.

Researchers obtained data from 2 large National Institutes of Health studies, the COPD study (SPIROMICS; ClinicalTrials.gov Identifier: NCT01969344) and the COPD Genetic Epidemiology study (COPDGene; ClinicalTrials.gov Identifier: NCT00608764) as well as subpopulations and outcome measures from both studies to assess the relationship between the diagnosis of emphysema by means of CT scan and patient outcomes, exacerbations, and mortality, with the intention of providing guidance to clinicians regarding the interpretation of radiologic findings and patient decision making.

Participants between the ages of 40 and 80 years with a history of smoking, with and without obstruction, were assessed for frequency of exacerbations, lung parenchyma on CT scan, and spirometry before and after receiving an administered dose of a short-acting bronchodilator. Study results demonstrated a linear, positive association between an increase in exacerbation frequency and higher mortality at approximately 5% of emphysema.

Researchers then divided the cohort into participants above and below the 5% emphysema threshold and found a significantly higher average exacerbation frequency in individuals with ≥5% emphysema in participants in both the COPDGene and SPIROMICS studies (0.69 vs 0.29 exacerbations/year, P =.03 and 0.46 vs 0.21 exacerbations/year, P <.001, respectively), as well as higher mortality in individuals with emphysema ≥5% compared with <5% (3.18 vs 0.98 deaths per 100 person-years; P <.001 and 2.66 vs 0.89 deaths per 100 person-years; P =.01). 

Of note, 26% and 15% of individuals with ≥5% emphysema and forced expiratory volume in 1 second/forced vital capacity <0.70 in the COPDGene and SPIROMICS studies, respectively, did not have a COPD diagnosis. In addition, individuals with <5% emphysema did not have greater symptoms or exacerbations, therefore the CT features captured were likely related to airway disease.

Researchers concluded there was a strong association between all-cause mortality and airflow obstruction. Findings support the use of combined criteria to identify individuals at a high risk for exacerbations and death. Therefore, clinicians should consider individuals with known COPD and CT results of ≥5% emphysema at greater risk for poor outcomes and should potentially initiate directed therapy.

Clinicians should also consider assessing spirometry in individuals without a prior diagnosis of COPD, and that CT results of ≥5% emphysema may potentially identify a subgroup of individuals with COPD who are also at high risk for poor outcomes.

Reference

Han MK, Tayob N, Murray, S, et al; for the COPDGene and SPIROMICS Investigators. Association between emphysema and COPD outcomes in COPDGene and SPIROMICS cohorts [published online February 27, 2018]. Am J Respir Crit Care Med. doi:10.1164/rccm.201801-0051LE