title: The asthma-chronic obstructive pulmonary disease overlap syndrome (ACOS): opportunities and challenges.
abstract: OBJECTIVE
  Some individuals share characteristics of asthma and chronic obstructive pulmonary disease (COPD). The asthma-COPD overlap syndrome (ACOS) has been defined as symptoms of increased variability of airflow in association with an incompletely reversible airflow obstruction. In this review, we present the latest findings in the diagnosis, characterization and management of ACOS.
  
  
  RESULTS
  Around 15-20% of COPD patients may have an ACOS. Patients with ACOS are characterized by increased reversibility of airflow obstruction, eosinophilic bronchial and systemic inflammation, and increased response to inhaled corticosteroids, compared with the remaining patients with COPD. Patients with ACOS have more frequent exacerbations, more wheezing and dyspnoea, but similar cough and sputum production compared with COPD.
  
  
  CONCLUSIONS
  The relevance of the ACOS is to identify patients with COPD who may have underlying eosinophilic inflammation that responds to inhaled corticosteroids. So far, the previous diagnosis of asthma in a patient with COPD is the more reliable criterion for ACOS. Ongoing studies will clarify if concentrations of blood eosinophils may be useful to identify this subgroup of patients with COPD. If this is the case, the interest of ACOS may shift to that of eosinophilic COPD, which is easier to diagnose and has clear therapeutic implications.
authors.affiliation: Pneumology Department, Hospital Universitari Vall d'Hebron, CIBER de Enfermedades Respiratorias (CIBERES), Barcelona, Spain.
authors.forename: Miriam
authors.initials: M
authors.lastname: Barrecheguren
authors.forename: Cristina
authors.initials: C
authors.lastname: Esquinas
authors.forename: Marc
authors.initials: M
authors.lastname: Miravitlles
mesh_terms: D000280:Administration, Inhalation; D000305:Adrenal Cortex Hormones / Q000627:therapeutic use*; D001249:Asthma / Q000175:diagnosis* / Q000188:drug therapy / Q000276:immunology / Q000503:physiopathology; D018450:Disease Progression; D004804:Eosinophils / Q000187:drug effects*; D006801:Humans; D007249:Inflammation / Q000175:diagnosis; D020641:Polymorphism, Single Nucleotide; D017410:Practice Guidelines as Topic; D015995:Prevalence; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis* / Q000188:drug therapy / Q000276:immunology / Q000503:physiopathology; D043562:Receptors, G-Protein-Coupled / Q000235:genetics; D012129:Respiratory Function Tests; D013183:Sputum / Q000276:immunology
chemical_list: D000305:Adrenal Cortex Hormones; C513334:GPR65 protein, human; D043562:Receptors, G-Protein-Coupled