Research in context
Evidence before this study
Before doing this study, we searched PubMed for clinical and epidemiological articles published in English between Jan 1, 2000, and March 1, 2015, using the following medical subject heading terms: “asthma-COPD overlap”, “asthma-COPD overlap syndrome”, “longitudinal”, “lung function”, and “mortality”. We excluded case reports and identified one study reporting a lower 4 year decline of forced expiratory volume in 1 s (FEV1) in individuals with asthma-chronic obstructive pulmonary disease (COPD) overlap than in those with COPD. When we did a new search for articles published in English between Jan 1, 2000, and Dec 15, 2015, using the same search terms, we identified one additional study describing FEV1 decline and hospital admissions due to exacerbations in young adults with asthma-COPD overlap during a 10 year observation. In this study, individuals with asthma-COPD overlap had a similar lung function decline but more hospital admissions than did participants with asthma.
Added value of this study
Our study takes advantage of a very long observation period (18–22 years). We differentiate between individuals with asthma-COPD overlap with early onset of asthma (before age of 40 years) and asthma-COPD overlap with late onset of asthma (aged 40 years or older at asthma onset). We show that decline of FEV1 is much faster in those with asthma-COPD with late-onset asthma, even exceeding the FEV1 decline among participants with COPD without asthma. In general, participants with asthma-COPD overlap had a high risk of hospital admissions. The subgroup with late-onset asthma also had very high mortality, from both all causes and respiratory diseases.
Implications of all the available evidence
The results show that in the long term, individuals with asthma-COPD overlap show considerable heterogeneity in lung function, hospital admissions, and survival, depending on the age when asthma manifests itself. In particular, the group with asthma-COPD overlap and late onset of asthma is susceptible and has a very poor prognosis according to lung function decline, hospital admissions, and survival.