Definitions of Chronic Obstructive Pulmonary Disease and Chronic Obstructive Pulmonary Disease Exacerbation: A Modified Delphi Survey / 결핵및호흡기질환

Background@#The Global Initiative for Chronic Obstructive Lung Disease (GOLD) update 2023 proposed new definitions of chronic obstructive pulmonary disease (COPD) and COPD exacerbation. However, an agreement on the definitions has not been made, either internationally or domestically. This study aimed to reach an agreement between experts on the new definitions of COPD and COPD exacerbation in South Korea. @*Methods@#A modified Delphi method was used to make an agreement on the definitions of COPD and COPD exacerbation proposed by the GOLD update 2023. We performed two rounds of the survey including 15 Korean experts on COPD, asthma, and tuberculosis. @*Results@#More than two-thirds of the experts agreed on 12 of the 13 statements related to the definitions of COPD and COPD exacerbation in the two rounds of the survey. The experts agreed on the definitions of COPD and COPD exacerbation that should be revised in line with the definitions proposed by the GOLD update 2023. However, the experts showed an uncertain opinion on the statement that the definition of COPD includes patients with persistent airflow obstruction due to bronchiectasis. @*Conclusion@#Based on this Delphi survey, experts’ agreement was made on the definitions of COPD and COPD exacerbation proposed by the GOLD update 2023.

When is LABA/LAMA Better than LAMA in GOLD Group B or D Patients for Reducing Acute Exacerbations of COPD? / 전남의대학술지

Long-acting  2 -agonist (LABA)/long-acting muscarinic-antagonist (LAMA) dual therapy has been found to be more effective than LAMA monotherapy in the treatment of chronic obstructive pulmonary disease (COPD). However, among patients with group B or D COPD, the characteristics of patients for whom LABA/LAMA dual therapy is superior to LAMA monotherapy in minimizing acute exacerbations remain unknown.With data from a prospective COPD cohort, subgroup analyses were conducted to determine whether LABA/LAMA dual therapy was superior to LAMA monotherapy in reducing the rate of acute exacerbations in group B and D COPD patients. Group B and D COPD patients taking LAMA or LABA/LAMA were enrolled according to the 2022 Global initiative for Chronic Obstructive Pulmonary Disease guidelines. A total of 737 patients were included in this study: 600 with group B COPD and 137 with group D COPD. Compared with patients taking LAMA monotherapy, those taking LABA/ LAMA had a significantly lower incidence of acute exacerbations over 1 year. In the subgroup of patients ≥70 years old, there was a significantly lower risk of severe COPD exacerbations among group B patients taking LABA/LAMA than among those taking LAMA monotherapy (odds ratio [OR], 0.258; 95% confidence interval [CI], 0.095– 0.703). In contrast, in the subgroup of group D patients with COPD Assessment Test scores ≥25, compared with LAMA monotherapy, LABA/LAMA treatment was associated with lower risk of severe COPD exacerbations (OR, 0.115; 95% CI, 0.018-0.749).The combination of LABA and LAMA was found to be superior to LAMA monotherapy, especially for treating older adults with group B COPD, as well as for group D patients with severe symptoms.

A Multicenter Study to Identify the Respiratory Pathogens Associated with Exacerbation of Chronic Obstructive Pulmonary Disease in Korea / 결핵및호흡기질환

Background@#Although respiratory tract infection is one of the most important factors triggering acute exacerbation of chronic obstructive pulmonary disease (AE-COPD), limited data are available to suggest an epidemiologic pattern of microbiology in South Korea. @*Methods@#A multicenter observational study was conducted between January 2015 and December 2018 across 28 hospitals in South Korea. Adult patients with moderate-to-severe acute exacerbations of COPD were eligible to participate in the present study. The participants underwent all conventional tests to identify etiology of microbial pathogenesis. The primary outcome was the percentage of different microbiological pathogens causing AE-COPD. A comparative microbiological analysis of the patients with overlapping asthma–COPD (ACO) and pure COPD was performed. @*Results@#We included 1,186 patients with AE-COPD. Patients with pure COPD constituted 87.9% and those with ACO accounted for 12.1%. Nearly half of the patients used an inhaled corticosteroid-containing regimen and one-fifth used systemic corticosteroids. Respiratory pathogens were found in 55.3% of all such patients. Bacteria and viruses were detected in 33% and 33.2%, respectively. Bacterial and viral coinfections were found in 10.9%. The most frequently detected bacteria were Pseudomonas aeruginosa (9.8%), and the most frequently detected virus was influenza A (10.4%). Multiple bacterial infections were more likely to appear in ACO than in pure COPD (8.3% vs. 3.6%, p=0.016). @*Conclusion@#Distinct microbiological patterns were identified in patients with moderate-to-severe AE-COPD in South Korea. These findings may improve evidence-based management of patients with AE-COPD and represent the basis for further studies investigating infectious pathogens in patients with COPD.

Developing a Diagnostic Bundle for Bronchiectasis in South Korea: A Modified Delphi Consensus Study / 결핵및호흡기질환

Background@#Because the etiologies of bronchiectasis and related diseases vary significantly among different regions and ethnicities, this study aimed to develop a diagnostic bundle for bronchiectasis in South Korea. @*Methods@#A modified Delphi method was used to develop expert consensus statements on a diagnostic bundle for bronchiectasis in South Korea. Initial statements proposed by a core panel, based on international bronchiectasis guidelines, were discussed in an online meeting and two email surveys by a panel of experts (≥70% agreement). @*Results@#The study involved 21 expert participants, and 30 statements regarding a diagnostic bundle for bronchiectasis were classified as recommended, conditional, or not recommended. The consensus statements of the expert panel were as follows: A standardized diagnostic bundle is useful in clinical practice; diagnostic tests for specific diseases, including immunodeficiency and allergic bronchopulmonary aspergillosis, are necessary when clinically suspected; initial diagnostic tests, including sputum microbiology and spirometry, are essential in all patients with bronchiectasis, and patients suspected with rare causes such as primary ciliary dyskinesia should be referred to specialized centers. @*Conclusion@#Based on this Delphi survey, expert consensus statements were generated including specific diagnostic, laboratory, microbiological, and pulmonary function tests required to manage patients with bronchiectasis in South Korea.

Differences in Clinical Characteristics of Invasive Tracheobronchial Aspergillosis according to the Presence of Invasive Pulmonary Aspergillosis / 결핵및호흡기질환

Background@#The association of invasive tracheobronchial aspergillosis (ITBA) with invasive pulmonary aspergillosis (IPA) is not well established. We aimed to compare clinical characteristics between patients who exhibited ITBA with IPA and those who exhibited isolated ITBA (iITBA). Additionally, the usefulness of serum or bronchial galactomannan (GM) tests in diagnosing ITBA was evaluated. @*Methods@#This retrospective single-center case-control study was conducted over a period of 4 years. Fifteen patients were enrolled after confirming the presence of ITBA using bronchoscopy-guided biopsy (iITBA, 7 vs. ITBA+IPA, 8). Clinical characteristics of patients and results obtained from serum or bronchial GM tests were compared between the two groups. Mortality was assessed using data collected from a 6-month follow-up period. @*Results@#The ITBA+IPA group showed a higher prevalence of hematologic malignancy (75% vs. 14%, p=0.029), a greater number of patients with multiple bronchial ulcers (75% vs. 14%, p=0.029), lower platelet counts (63,000/μL vs. 229,000/μL, p<0.001), and a mortality rate which was significantly higher (63% vs. 0%, p=0.026) than the iITBA group. In the ITBA+IPA group, 57% of patients tested positive according to the serum GM assay, whereas in the iITBA group, all patients tested negative (p=0.070). The bronchial GM level was high in both groups, but there was no significant difference between them. @*Conclusion@#Patients with ITBA+IPA had a greater number of hematologic malignancies with lower platelet counts and a poorer prognosis than patients diagnosed with iITBA. Findings obtained from bronchoscopy and bronchial GM tests were more useful in diagnosing ITBA than the serum GM test results.

Differences in Clinical Characteristics of Invasive Tracheobronchial Aspergillosis according to the Presence of Invasive Pulmonary Aspergillosis / 결핵및호흡기질환

Background@#The association of invasive tracheobronchial aspergillosis (ITBA) with invasive pulmonary aspergillosis (IPA) is not well established. We aimed to compare clinical characteristics between patients who exhibited ITBA with IPA and those who exhibited isolated ITBA (iITBA). Additionally, the usefulness of serum or bronchial galactomannan (GM) tests in diagnosing ITBA was evaluated. @*Methods@#This retrospective single-center case-control study was conducted over a period of 4 years. Fifteen patients were enrolled after confirming the presence of ITBA using bronchoscopy-guided biopsy (iITBA, 7 vs. ITBA+IPA, 8). Clinical characteristics of patients and results obtained from serum or bronchial GM tests were compared between the two groups. Mortality was assessed using data collected from a 6-month follow-up period. @*Results@#The ITBA+IPA group showed a higher prevalence of hematologic malignancy (75% vs. 14%, p=0.029), a greater number of patients with multiple bronchial ulcers (75% vs. 14%, p=0.029), lower platelet counts (63,000/μL vs. 229,000/μL, p<0.001), and a mortality rate which was significantly higher (63% vs. 0%, p=0.026) than the iITBA group. In the ITBA+IPA group, 57% of patients tested positive according to the serum GM assay, whereas in the iITBA group, all patients tested negative (p=0.070). The bronchial GM level was high in both groups, but there was no significant difference between them. @*Conclusion@#Patients with ITBA+IPA had a greater number of hematologic malignancies with lower platelet counts and a poorer prognosis than patients diagnosed with iITBA. Findings obtained from bronchoscopy and bronchial GM tests were more useful in diagnosing ITBA than the serum GM test results.

Whole lung lavage using a rapid infusion system to treat a patient with pulmonary alveolar proteinosis / 영남의대학술지

Whole lung lavage (WLL) is a therapeutic procedure to remove accumulated material by infusing and draining the lungs with lavage fluid. This procedure has been regarded as the current standard of care to treat pulmonary alveolar proteinosis. However, the WLL protocol has not yet been standardized and the technique has been refined and modified a number of times. A rapid infusion system is a device used to infuse blood or other fluids at precise rates and normothermic conditions. This device is not typically used in WLL, which relies on the passive infusion of fluids using the gravitational force. However, in this study we performed WLL using a rapid infusion system, since we aimed to take advantage of its shorter operation time and greater degree of control over fluid volume and temperature. The patient’s symptoms improved without the occurrence of any complications.

Update on pharmacotherapy for adult bronchiectasis

Bronchiectasis refers to abnormal dilatation of the bronchi, which leads to the failure of mucus clearance and increased risk of infection. Pharmacotherapy for stable bronchiectasis includes oral or inhaled mucoactive agents, anti-inflammatory therapy, inhaled bronchodilators, long-term antibiotics, and long-term macrolide treatment.Among them, mucoactive agents are the most common adjunctive agents to airway clearance techniques. When patients with impaired lung function suffer from dyspnea, inhaled bronchodilators may be prescribed to relieve the symptom. Long-term macrolide treatment has been proven to prevent exacerbation in patients with frequent bronchiectasis exacerbation. If exacerbation occurs despite the above mentioned treatments, one or two weeks of antibiotics should be prescribed to cover respiratory bacteria that include Pseudomonas aeruginosa. Because evidence supporting the use of pharmacotherapy for bronchiectasis is weak, further research is warranted.

Exhaled Nitric Oxide in Patients with Stable Chronic Obstructive Pulmonary Disease: Clinical Implications of the Use of Inhaled Corticosteroids / 결핵

Circulating Tumor Cell Number Is Associated with Primary Tumor Volume in Patients with Lung Adenocarcinoma / 결핵

Exhaled Nitric Oxide in Patients with Stable Chronic Obstructive Pulmonary Disease: Clinical Implications of the Use of Inhaled Corticosteroids / 결핵및호흡기질환

BACKGROUND@#Fractional exhaled nitric oxide (FeNO) is regarded as a potential biomarker for identifying eosinophilic inflammation. We aimed to evaluate the clinical implication of FeNO and its influence on inhaled corticosteroids (ICS) prescription rate in Korean chronic obstructive pulmonary disease (COPD) patients.@*METHODS@#FeNO level and its association with clinical features were analyzed. Changes in the prescription rate of ICS before and after FeNO measurement were identified.@*RESULTS@#A total of 160 COPD patients were divided into increased (≥25 parts per billion [ppb], n=74) and normal (<25 ppb, n=86) FeNO groups according to the recommendations from the American Thoracic Society. Compared with the normal FeNO group, the adjusted odds ratio for having history of asthma without wheezing and with wheezing in the increased FeNO group were 2.96 (95% confidence interval [CI], 1.40–6.29) and 4.24 (95% CI, 1.37–13.08), respectively. Only 21 out of 74 patients (28.4%) with increased FeNO prescribed ICS-containing inhaler and 18 of 86 patients (20.9%) with normal FeNO were given ICS-containing inhaler. Previous exacerbation, asthma, and wheezing were the major factors to maintain ICS at normal FeNO level and not to initiate ICS at increased FeNO level.@*CONCLUSION@#Increased FeNO was associated with the history of asthma irrespective of wheezing. However, FeNO seemed to play a subsidiary role in the use of ICS-containing inhalers in real-world clinics, which was determined with prior exacerbation and clinical features suggesting Th2 inflammation.

Circulating Tumor Cell Number Is Associated with Primary Tumor Volume in Patients with Lung Adenocarcinoma / 결핵및호흡기질환

BACKGROUND@#Circulating tumor cells (CTCs) are frequently detected in patients with advanced-stage malignant tumors and could act as a predictor of poor prognosis. However, there is a paucity of data on the relationship between CTC number and primary tumor volume in patients with lung cancer. Therefore, our study aimed to evaluate the relationship between CTC number and primary tumor volume in patients with lung adenocarcinoma.@*METHODS@#We collected blood samples from 21 patients with treatment-naive lung adenocarcinoma and 73 healthy individuals. To count CTCs, we used a CTC enrichment method based on fluid-assisted separation technology. We compared CTC numbers between lung adenocarcinoma patients and healthy individuals using propensity score matching, and performed linear regression analysis to analyze the relationship between CTC number and primary tumor volume in lung adenocarcinoma patients.@*RESULTS@#CTC positivity was significantly more common in lung adenocarcinoma patients than in healthy individuals (p<0.001). The median primary tumor volume in CTC-negative and CTC-positive patients was 10.0 cm³ and 64.8 cm³, respectively. Multiple linear regression analysis showed that the number of CTCs correlated with primary tumor volume in lung adenocarcinoma patients (β=0.903, p=0.002). Further subgroup analysis showed a correlation between CTC number and primary tumor volume in patients with distant (p=0.024) and extra-thoracic (p=0.033) metastasis (not in patients with distant metastasis).@*CONCLUSION@#Our study showed that CTC numbers may be associated with primary tumor volume in lung adenocarcinomas patients, especially in those with distant metastasis.

Exhaled Nitric Oxide in Patients with Stable Chronic Obstructive Pulmonary Disease: Clinical Implications of the Use of Inhaled Corticosteroids / 결핵및호흡기질환

BACKGROUND@#Fractional exhaled nitric oxide (FeNO) is regarded as a potential biomarker for identifying eosinophilic inflammation. We aimed to evaluate the clinical implication of FeNO and its influence on inhaled corticosteroids (ICS) prescription rate in Korean chronic obstructive pulmonary disease (COPD) patients.@*METHODS@#FeNO level and its association with clinical features were analyzed. Changes in the prescription rate of ICS before and after FeNO measurement were identified.@*RESULTS@#A total of 160 COPD patients were divided into increased (≥25 parts per billion [ppb], n=74) and normal (<25 ppb, n=86) FeNO groups according to the recommendations from the American Thoracic Society. Compared with the normal FeNO group, the adjusted odds ratio for having history of asthma without wheezing and with wheezing in the increased FeNO group were 2.96 (95% confidence interval [CI], 1.40–6.29) and 4.24 (95% CI, 1.37–13.08), respectively. Only 21 out of 74 patients (28.4%) with increased FeNO prescribed ICS-containing inhaler and 18 of 86 patients (20.9%) with normal FeNO were given ICS-containing inhaler. Previous exacerbation, asthma, and wheezing were the major factors to maintain ICS at normal FeNO level and not to initiate ICS at increased FeNO level.@*CONCLUSION@#Increased FeNO was associated with the history of asthma irrespective of wheezing. However, FeNO seemed to play a subsidiary role in the use of ICS-containing inhalers in real-world clinics, which was determined with prior exacerbation and clinical features suggesting Th2 inflammation.

Circulating Tumor Cell Number Is Associated with Primary Tumor Volume in Patients with Lung Adenocarcinoma / 결핵및호흡기질환

BACKGROUND@#Circulating tumor cells (CTCs) are frequently detected in patients with advanced-stage malignant tumors and could act as a predictor of poor prognosis. However, there is a paucity of data on the relationship between CTC number and primary tumor volume in patients with lung cancer. Therefore, our study aimed to evaluate the relationship between CTC number and primary tumor volume in patients with lung adenocarcinoma.@*METHODS@#We collected blood samples from 21 patients with treatment-naive lung adenocarcinoma and 73 healthy individuals. To count CTCs, we used a CTC enrichment method based on fluid-assisted separation technology. We compared CTC numbers between lung adenocarcinoma patients and healthy individuals using propensity score matching, and performed linear regression analysis to analyze the relationship between CTC number and primary tumor volume in lung adenocarcinoma patients.@*RESULTS@#CTC positivity was significantly more common in lung adenocarcinoma patients than in healthy individuals (p<0.001). The median primary tumor volume in CTC-negative and CTC-positive patients was 10.0 cm³ and 64.8 cm³, respectively. Multiple linear regression analysis showed that the number of CTCs correlated with primary tumor volume in lung adenocarcinoma patients (β=0.903, p=0.002). Further subgroup analysis showed a correlation between CTC number and primary tumor volume in patients with distant (p=0.024) and extra-thoracic (p=0.033) metastasis (not in patients with distant metastasis).@*CONCLUSION@#Our study showed that CTC numbers may be associated with primary tumor volume in lung adenocarcinomas patients, especially in those with distant metastasis.

Adherence to the GOLD Guideline in COPD Management of South Korea: Findings from KOCOSS Study 2011–2018 / 전남의대학술지

The guidelines for chronic obstructive pulmonary disease (COPD) treatment are important for the management of the disease. However, studies regarding the treatment adherence to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines have been scarce in Korea. Therefore, to examine the adherence to the GOLD guidelines, we examined the patterns of prescribed medication in COPD patients from 2011 to 2018. Patients were classified as having been appropriately and inappropriately treated (overtreatment or undertreatment) for the GOLD group. Appropriate medical therapy was defined as using the first choice or alternative choice drug recommended in the GOLD guidelines. Inappropriate therapy was classified as overtreatment or undertreatment in accordance with the categorization in the GOLD guidelines. According to treatment of 2011 GOLD guidelines, there was inappropriate treatment in 52.3% in group A, 47.3% in group B, 56.3% in group C, and 17.8% in group D. According to treatment of 2017 GOLD guidelines, there was inappropriate treatment in 66.7% in group A, 45.3% in group B, 14.3% in group C, and 24.0% in group D. The common type of inappropriate COPD treatment is overtreatment, with inhaled corticosteroid (ICS) containing regimens. In conclusions, adherence to the GOLD guideline by the pulmonologist in clinical practice is still low in Korea. Therefore, we need better strategies to both optimize the use of the guidelines and adhere to the guidelines as well.

Corrigendum: Elucidation of Bacterial Pneumonia-Causing Pathogens in Patients with Respiratory Viral Infection / 결핵및호흡기질환

In this article, the ethical statement was missing.

Use of serology and polymerase chain reaction to detect atypical respiratory pathogens during acute exacerbation of chronic obstructive pulmonary disease

BACKGROUND/AIMS: To use serological and multiplex polymerase chain reaction (PCR) assays to examine sputum samples from patients experiencing acute exacerbation of chronic obstructive pulmonary disease (AECOPD) for the presence of atypical pathogens, including Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella pneumophila. METHODS: From September 2012 to February 2014, 341 patients with AECOPD attending outpatient clinics were enrolled as part of a randomized, double-blind, multicenter study. A commercial enzyme-linked immunosorbent assay was used to measure serum immunoglobulin M (IgM) and IgG antibody titers on the first day of the study and at 36 days post-enrollment. Multiplex PCR was used to test sputum samples for the presence of atypical pathogens. A urinary antigen test for L. pneumophila was performed on the first day. RESULTS: Nineteen patients (5.6%) showed serological evidence of acute infection with M. pneumoniae. Also, one and seven patients (2%) showed serological evidence of acute infection with C. pneumoniae and L. pneumophila, respectively. All DNA samples were negative for M. pneumoniae, C. pneumoniae, and L. pneumophila according to PCR. Only one urine sample was positive for L. pneumophila antigen, but serologic evidence was lacking. CONCLUSIONS: Serological testing suggested that infection by atypical pathogens during AECOPD was relatively uncommon. In addition, PCR provided no direct evidence of infection by atypical pathogens. Thus, atypical pathogens may not be a major cause of AECOPD in South Korea.

Treatment and prevention of acute exacerbation of chronic obstructive pulmonary disease

Acute exacerbation of chronic obstructive pulmonary disease (COPD) is defined as an acute aggravation of the patient's respiratory symptoms, particularly cough, sputum production, and dyspnea, which requires a change of medication. COPD exacerbation leads to an accelerated decline in lung function, poorer health status, and is the main cause of hospital admission and death in patients with COPD. A majority of COPD exacerbations are triggered by respiratory infection. The Management of acute exacerbation of COPD consists of systemic corticosteroids, antibiotics, and inhaled short-acting bronchodilators. Oxygen supplementation is an essential component of treatment to improve hypoxemia. Noninvasive or invasive ventilator support is necessary for COPD patients with severe exacerbation, particularly associated with hypercapnic respiratory failure. The Korean clinical practice guideline for COPD was revised in 2018 by the members of the Korean Academy of Tuberculosis and Respiratory Diseases as well as participating members of the Health Insurance Review and Assessment Service. The purpose of this review is to provide an overview of the treatment and prevention strategies recommended in the 2018 Korean Academy of Tuberculosis and Respiratory Diseases for patient with acute exacerbation of COPD.

Treatment and prevention of acute exacerbation of chronic obstructive pulmonary disease

Acute exacerbation of chronic obstructive pulmonary disease (COPD) is defined as an acute aggravation of the patient's respiratory symptoms, particularly cough, sputum production, and dyspnea, which requires a change of medication. COPD exacerbation leads to an accelerated decline in lung function, poorer health status, and is the main cause of hospital admission and death in patients with COPD. A majority of COPD exacerbations are triggered by respiratory infection. The Management of acute exacerbation of COPD consists of systemic corticosteroids, antibiotics, and inhaled short-acting bronchodilators. Oxygen supplementation is an essential component of treatment to improve hypoxemia. Noninvasive or invasive ventilator support is necessary for COPD patients with severe exacerbation, particularly associated with hypercapnic respiratory failure. The Korean clinical practice guideline for COPD was revised in 2018 by the members of the Korean Academy of Tuberculosis and Respiratory Diseases as well as participating members of the Health Insurance Review and Assessment Service. The purpose of this review is to provide an overview of the treatment and prevention strategies recommended in the 2018 Korean Academy of Tuberculosis and Respiratory Diseases for patient with acute exacerbation of COPD.

Asthma-COPD Overlap Shows Favorable Clinical Outcomes Compared to Pure COPD in a Korean COPD Cohort

PURPOSE: Comparisons of the characteristics of chronic obstructive pulmonary disease (COPD) and asthma-COPD overlap syndrome (ACOS) have been the focus of several studies since the diseases were defined by the Global Initiative for Asthma and Global Initiative for Chronic Obstructive Lung Disease guidelines. However, no consensus is available yet. In this study, we aimed to compare the characteristics of asthma-COPD overlap (ACO) and COPD. METHODS: We retrospectively reviewed 1,504 patients with COPD in a Korean COPD Subtype Study cohort. The occurrence of ACO was defined as a positive response to a bronchodilator (an increase in forced expiratory volume in 1 second [FEV1] of 12% and 200 mL). RESULTS: Among 1,504 patients with COPD, 223 (14.8%) were diagnosed with ACO. Men (95.5%) and current smokers (32.9%) were more prevalent in the ACO group compared with the pure COPD group (90.5% and 25.3%, respectively; P=0.015 and P=0.026, respectively). Patients with ACO had a better quality of life (St. George's Respiratory Questionnaire for COPD score=31.0±18.0 [mean±standard deviation]) than those with pure COPD (35.3±19.1) (P=0.002). Although the prevalence of acute exacerbation was not different between the 2 groups, patients with severe exacerbation required hospital admission significantly more frequently in the pure COPD group than in the ACO group. Patients with ACO showed a higher likelihood of FEV1 recovery than those with pure COPD (P<0.001). CONCLUSIONS: We suggest that ACO is characterized by less severe symptoms, and therefore it might lead to rare severe exacerbation and the possibility of lung function recovery.