• Annelies Slats and Christian Taube.
• Department of Pulmonology, Leiden University Medical Center, Leiden, The Netherlands.
• Ther Adv Respir Dis. 2016 Feb 1; 10 (1): 57-71.

AbstractAsthma and chronic obstructive pulmonary disease (COPD) are different disease entities. They are both clinical diagnoses, with diagnostic tools to discriminate between one another. However, especially in older patients (>55 years) it seems more difficult to differentiate between asthma and COPD. This has led to the definition of a new phenotype called asthma COPD overlap syndrome (ACOS). However, our understanding of ACOS is at a very preliminary stage, as most research has involved subjects with existing diagnoses of asthma or COPD from studies with different definitions for ACOS. This has led to different and sometimes opposing results between studies on several features of ACOS, also depending on the comparison with COPD alone, asthma alone or both, which are summarized in this review.We suggest not using the term ACOS for a patient with features of both asthma and COPD, but to describe a patient with chronic obstructive airway disease as completely as possible, with regard to characteristics that determine treatment response (e.g. eosinophilic inflammation) and prognosis (such as smoking status, exacerbation rate, fixed airflow limitation, hyperresponsiveness, comorbidities). This will provide a far more clinically relevant diagnosis, and would aid in research on treatment in more homogenous groups of patients with chronic airways obstruction. More research is certainly needed to develop more evidence-based definitions for this patient group and to evaluate biomarkers, which will help to further classify these patients, treat them more adequately and unravel the underlying pathophysiological mechanism. © The Author(s), 2015.

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