The current study found the increases in FEV1 in response to treatment with ICS were significantly higher in the COPD with asthma group, although no significant difference was found in the increases in FEV1 in response to β2-agonist between the two groups. Both the peripheral eosinophil counts and sputum eosinophil counts were significantly higher in the COPD with asthma group. Chest HRCT showed that the prevalence of patients with BWT was significantly higher in the COPD with asthma group. A significant correlation was observed between the increases in FEV1 in response to treatment with ICS and sputum eosinophil counts, and between the increases in FEV1 in response to treatment with ICS and the grade of BWT. Receiver operator characteristic curve analysis revealed 82.4% sensitivity and 84.8% specificity of sputum eosinophil count for detecting COPD with asthma, using 2.5% as the cutoff value.
The underlying chronic airway inflammation in COPD is very different than that in asthma. Asthma is traditionally characterized by an eosinophilic inflammation that affects all the airways but not lung parenchyma, and it is linked to airway hyperresponsiveness.13
However, asthmatic patients that smoke develop pathological features similar to COPD.14
Some patients with COPD may demonstrate features of asthma, such as a mixed inflammatory pattern with increased eosinophils,15
and an increased sputum eosinophil count has been reported to be related to an improvement in FEV1
following treatment with ICS in COPD.16
The peripheral eosinophil counts and sputum eosinophil counts were significantly higher, and the reversibility due to a response to the treatment with ICS was better in the COPD with asthma group in the current series. These results suggest that COPD patients with asthmatic symptoms also had features of asthma such as a mixed inflammatory pattern with increased eosinophils. A significant correlation was observed between the increases in FEV1
in response to treatment with ICS and sputum eosinophil counts, thus suggesting that high sputum eosinophil counts might be a good predictor of response to ICS.
Pulmonary function testing with bronchodilators has been used to differentiate asthma from COPD, with COPD demonstrating a smaller response.17
However, some patients with COPD showed reversibility, which is defined as an increase in FEV1
of >12% and 200 mL from baseline values, in response to bronchodilators.18
The degree of reversibility of airflow limitation is no longer recommended for diagnosis, differential diagnosis with asthma, or predicting the response to longer treatment with bronchodilators or glucocorticosteroids according to the Global Initiative for Chronic Obstructive Lung Disease guidelines.1
The current study found no significant difference in the increases in FEV1
in response to β2
-agonist between the two groups, and this result was consistent with the findings of previous reports.
The major differences in airway remodeling between asthma and COPD are the thickening of the reticular layer under the basement membrane with submucosal infiltration of a large number of eosinophils and the proliferation of mucosal blood vessels found in asthma. On the contrary, it seems that fixed airway obstruction is the final result of structural changes of peripheral airways and lung parenchyma in COPD.13
Therefore, these diseases have different pathologies of airway remodeling. However, it is difficult to clinically differentiate between COPD and asthma in some patients with irreversible airflow limitation.13
Airway remodeling is thought to be the main cause of irreversible airflow limitation in older asthmatic patients. The presence of a normal diffusing capacity for DLCO may be useful to differentiate asthma with airway remodeling from COPD. However, COPD has morphological phenotypes on chest HRCT and some patients with COPD that show normal capacity for DLCO are classified into the absence of emphysema phenotype.2
There is a possibility that the COPD with asthma group included asthmatic patients with airway remodeling in this study, because it is sometimes difficult to clinically differentiate such patients from COPD patients who are classified into the absence of emphysema phenotype. Nonetheless, ICS should be considered earlier as a potential treatment in patients who are clinically diagnosed to have COPD with asthmatic symptoms. While DLCO was significantly lower in the COPD with asthma group, this may be because the mean value of LAA score was lower in the COPD with asthma group. Alternatively, this may be because asthmatic patients show relatively higher values of DLCO because allergic inflammation may affect pulmonary circulation.21
HRCT used to quantify abnormalities of the airways due to airway remodeling in asthma, and the HRCT scan score is correlated with the severity of asthma and airflow obstruction.22
The absence of emphysema phenotype and emphysema with BWT phenotype are associated with a better responsiveness to treatment with ICS in COPD patients.2
The prevalence of patients with BWT was significantly higher in the COPD with asthma group on chest HRCT in the current series. A significant correlation was observed between the increases in FEV1
in response to treatment with ICS and the grade of BWT. The current results were consistent with those of previous reports and suggest that BWT on chest HRCT might be a good predictor of response to ICS.
One limitation of this retrospective study is that the assessment of emphysema was done by a visual scoring method, rather than using a software-based quantification of emphysema. However, the reproducibility of such visual scoring has been demonstrated in a previous report.3
Another limitation is the lack of statistical power because the sample size was small for the absence of emphysema phenotype (n = 4 in the COPD with asthma group and n = 8 in the COPD without asthma group) which is generally lower, accounting for only about 22% of COPD.2
Another limitation of these findings is associated with the fact that while many statistical differences and correlations were observed, these results by themselves do not imply cause and effect.