The asthma-COPD overlap syndrome: do we really need another syndrome in the already complex matrix of airway disease?

Abstract

The term asthma-COPD overlap syndrome (ACOS) is one of multiple terms used to describe patients with characteristics of both COPD and asthma, representing ~20% of patients with obstructive airway diseases. The recognition of both sets of morbidities in patients is important to guide practical treatment decisions. It is widely recognized that patients with COPD and coexisting asthma present with a higher disease burden, despite the conceptual expectation that the "reversible" or "treatable" component of asthma would allow for more effective management and better outcomes. However, subcategorization into terms such as ACOS is complicated by the vast spectrum of heterogeneity that is encapsulated by asthma and COPD, resulting in different clinical clusters. In this review, we discuss the possibility that these different clusters are suboptimally described by the umbrella term "ACOS", as this additional categorization may lead to clinical confusion and potential inappropriate use of resources. We suggest that a more clinically relevant approach would be to recognize the extreme variability and the numerous phenotypes encompassed within obstructive airway diseases, with various degrees of overlapping in individual patients. In addition, we discuss some of the evidence to be considered when making practical decisions on the treatment of patients with overlapping characteristics between COPD and asthma, as well as the potential options for phenotype and biomarker-driven management of airway disease with the aim of providing more personalized treatment for patients. Finally, we highlight the need for more evidence in patients with overlapping disease characteristics and to facilitate better characterization of potential treatment responders.

Keywords: ACOS; COPD; asthma; chronic bronchitis; emphysema; overlap syndrome.

Figure 1

Prevalence of overlapping asthma and COPD in studies of varying designs in a cluster analysis (following a systematic literature search). Notes: A systematic literature review of cluster analyses of asthma and COPD was performed. Articles from 2009 to September 1, 2014, dealing with prevalence, morbidity, and treatment of asthma–COPD overlap, were identified and reviewed. The prevalence of overlapping asthma and COPD was reported in epidemiological studies (•), studies in severe asthma (■), studies in adult asthma (▼), and studies in COPD (▲). Reproduced from Thorax, Gibson PG, McDonald VM. 70(7), 683–691. Copyright 2015. With permission from BMJ Publishing Group Ltd.

Figure 2

Pathophysiology of asthma, COPD, and overlap. Notes: Data taken from Postma et al and Barnes et al. Abbreviations: TGFβ, tumor growth factor β; T_H1, T-helper 1; T_C1, type 1 cytotoxic T cells.

Figure 3

Proposed algorithmic approach for patients with overlapping clinical characteristics of asthma and COPD. Abbreviation: ICS, inhaled corticosteroid.