title: Quantitative computed tomography measurements of emphysema for diagnosing asthma-chronic obstructive pulmonary disease overlap syndrome.
abstract: BACKGROUND
  The diagnostic criteria of asthma-COPD overlap syndrome (ACOS) are controversial. Emphysema is characteristic of COPD and usually does not exist in typical asthma patients. Emphysema in patients with asthma suggests the coexistence of COPD. Quantitative computed tomography (CT) allows repeated evaluation of emphysema noninvasively. We investigated the value of quantitative CT measurements of emphysema in the diagnosis of ACOS.
  
  
  METHODS
  This study included 404 participants; 151 asthma patients, 125 COPD patients, and 128 normal control subjects. All the participants underwent pulmonary function tests and a high-resolution CT scan. Emphysema measurements were taken with an Airway Inspector software. The asthma patients were divided into high and low emphysema index (EI) groups based on the percentage of low attenuation areas less than -950 Hounsfield units. The characteristics of asthma patients with high EI were compared with those having low EI or COPD.
  
  
  RESULTS
  The normal value of percentage of low attenuation areas less than -950 Hounsfield units in Chinese aged >40 years was 2.79%±2.37%. COPD patients indicated more severe emphysema and more upper-zone-predominant distribution of emphysema than asthma patients or controls. Thirty-two (21.2%) of the 151 asthma patients had high EI. Compared with asthma patients with low EI, those with high EI were significantly older, more likely to be male, had more pack-years of smoking, had more upper-zone-predominant distribution of emphysema, and had greater airflow limitation. There were no significant differences in sex ratios, pack-years of smoking, airflow limitation, or emphysema distribution between asthma patients with high EI and COPD patients. A greater number of acute exacerbations were seen in asthma patients with high EI compared with those with low EI or COPD.
  
  
  CONCLUSIONS
  Asthma patients with high EI fulfill the features of ACOS, as described in the Global Initiative for Asthma and Global Initiative for Chronic Obstructive Lung Disease guidelines. Quantitative CT measurements of emphysema may help in diagnosing ACOS.
authors.affiliation: Department of Pulmonary Medicine, Qilu Hospital, Shandong University, Jinan, People's Republic of China.
authors.forename: Mengshuang
authors.initials: M
authors.lastname: Xie
authors.affiliation: Department of Pulmonary Medicine, Qilu Hospital, Shandong University, Jinan, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Pulmonary Medicine, Qilu Hospital, Shandong University, Jinan, People's Republic of China.
authors.forename: Shuang
authors.initials: S
authors.lastname: Dou
authors.affiliation: Department of Pulmonary Medicine, Qilu Hospital, Shandong University, Jinan, People's Republic of China.
authors.forename: Liwei
authors.initials: L
authors.lastname: Cui
authors.affiliation: Department of Pulmonary Medicine, Qilu Hospital, Shandong University, Jinan, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: Xiao
mesh_terms: D000368:Aged; D001249:Asthma / Q000000981:diagnostic imaging* / Q000503:physiopathology; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D003937:Diagnosis, Differential; D018450:Disease Progression; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging* / Q000503:physiopathology; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging* / Q000503:physiopathology; D012720:Severity of Illness Index; D013147:Spirometry; D013577:Syndrome; D014057:Tomography, X-Ray Computed; D014797:Vital Capacity
keywords: COPD; asthma; emphysema; overlap syndrome; quantitative CT