Atopy and Physician-Diagnosed Asthma May Help Identify Asthma-COPD Overlap

The presence of atopy and clinician diagnosed asthma may aid in the identification of asthma and chronic obstructive pulmonary disease (COPD) overlap (ACO), according to study results published in Respirology. 

This prospective, multicenter study included 522 patients with COPD from the Canadian Cohort Obstructive Lung Disease study, 258 (49%) of whom were considered to have non-ACO COPD. All COPD diagnoses were defined by post-bronchodilator forced exhaled volume during the first second/forced vital capacity (FEV₁/FVC) of <0.70. In addition to phone interviews every 3 months, in-person assessments took place at baseline, 1.5 years, and 3 years and included questionnaires, blood tests, chest computed tomography scans, and pulmonary function assessments. Data were collected between 2009 and 2017.

The researchers examined 7 definitions for ACO. Continuous variables were analyzed using the general linear model, whereas logistic regression was used for categorical variables with adjustments for certain demographic characteristics. Variables that differed significantly between the ACO and non-ACO groups were further analyzed in multivariate stepwise logistic regression.

Each of the 7 ACO definitions described between 3.8% and 31% of the 264 participants with ACO. Compared with the ACO group, participants with non-ACO COPD had a statistically nonsignificantly lower FEV₁ annual decline (-38.1 mL/y [95% CI, -49.3 to -26.9] vs -81.1 mL/y [95% CI, -116.5 to -45.6] for non-ACO vs ACO definition 2, respectively). Non-ACO participants were more likely to be slow decliners than those with ACO and had fewer exacerbations, symptoms, and comorbidities. St. George’s Respiratory Questionnaire score decreased at follow-up for the majority of the ACO group and increased for non-ACO COPD. Participants with non-ACO had higher scores for emphysema (126 vs 118) and bronchiolitis (56 vs 43). Those definitions including atopy and/or clinician diagnosed asthma identified participants differing the most from those with COPD.

Study limitations included self-reporting of atopy and asthma diagnoses, an inability to include the whole sample in a longitudinal analysis, a relatively short follow-up period, the use of baseline post-bronchodilator FEV₁/FVC <0.7 to diagnose COPD, a lack of biomarkers, and the unavailability of blood and inflammation data.

The study researchers concluded that “simple clinical definitions can help for the diagnosis of ACO,” and that “individuals with ACO had different characteristics and poorer outcomes than non-ACO.” Furthermore, “atopy and a previous physician diagnosis of asthma were the most consistent over time.” However, “the utility of bronchodilator reversibility did not provide incremental benefit in the diagnosis and were less stable.” Further studies “using biomarkers and airway inflammation patterns” could help assess whether “subjects with ACO have different disease progression than non-ACO COPD.”

Disclosure: This clinical trial was supported by several pharmaceutical companies. Please see the original reference for a full list of authors’ disclosures.

Reference

Barrecheguren M, Pinto L, Mostafavi‐Pour‐Manshadi SMY, et al; for the CanCOLD Collaborative Research Group and the Canadian Respiratory Research Network. Identification and definition of asthma–COPD overlap: the CanCOLD study [published online February 16, 2020]. Respirology. doi:10.1111/resp.13780