title: Understanding the pathophysiology of the asthma-chronic obstructive pulmonary disease overlap syndrome.
abstract: OBJECTIVE
  The review will provide an update on the pathophysiology and studies of inflammation associated with the asthma-chronic obstructive pulmonary disease (COPD) overlap syndrome (ACOS) and the mechanism(s) responsible for persistent expiratory airflow limitation in never-smoked asthma patients who develop loss of lung elastic recoil consistent with an asthma-COPD clinical phenotype (ACOS in nonsmokers).
  
  
  RESULTS
  Patients with a clinical diagnosis of ACOS have more frequent respiratory exacerbations and hospitalizations than COPD patients without ACOS. ACOS patients should be treated with inhaled corticosteroids, short and long-acting β2-agonist, and long-acting muscarinic receptor antagonist. Biomarker work suggests that a molecular phenotype of ACOS (e.g., elevated markers of eosinophilic or type 2 inflammation) incompletely corresponds to clinical phenotypes. Recently, we reported sentinel observation of unsuspected mild diffuse centrilobular emphysema in never-smoked asthma patients at autopsy, despite mild changes in lung computed tomography and normal diffusing capacity.
  
  
  CONCLUSIONS
  Recent studies have shown that subgroups of COPD and asthma patients may have overlapping immune responses. Never-smoked asthma patients may have persistent expiratory airflow limitation because of loss of lung elastic recoil. This may be because of unsuspected centrilobular emphysema detected at autopsy, and not easily diagnosed on lung computed tomography and diffusing capacity.
authors.affiliation: aPulmonary Division, Department of Medicine, Lakewood Regional Medical Center (LRMC), Lakewood, California and Geffen School of Medicine at UCLA Medical Center, Los Angeles bDepartment of Medicine, Division of Pulmonary, Critical Care, Allergy, and Sleep, and Cardiovascular Research Institute, University of California, San Francisco cDepartments of Medicine, Physiology, and Radiology, and Cardiovascular Research Institute, University of California, San Francisco, California, USA.
authors.forename: Arthur F
authors.initials: AF
authors.lastname: Gelb
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Christenson
authors.forename: Jay A
authors.initials: JA
authors.lastname: Nadel
mesh_terms: D001249:Asthma / Q000150:complications / Q000503:physiopathology*; D006801:Humans; D007249:Inflammation / Q000503:physiopathology; D010641:Phenotype; D029424:Pulmonary Disease, Chronic Obstructive / Q000209:etiology / Q000503:physiopathology*; D012907:Smoking