Overview of mechanisms: Asthma versus chronic obstructive pulmonary disease

Asthma and chronic obstructive pulmonary disease (COPD) are considered distinct obstructive lung diseases with different diagnostic, mechanisms and management strategies. Inflammation, structural alterations and remodeling occur in both asthma and COPD, however there are differences in the inflammatory mechanisms, the affected structures and the predominant anatomic sites. The differences are most evident when nonsmoking asthmatics and smokers with COPD from polar ends of the spectrum of reversibility are compared. As disease progresses and becomes severe, the patterns of inflammation become more similar. Moreover in the clinical setting, combinations of asthma-related and COPD-related phenotypes are not uncommon. Several studies have emphasized the similarities and the differences between the diverse phenotypes of these diseases. Whether it actually matters or not can be a difficult question to answer because significant physiologic and pathologic overlap exists between these diseases. However given the complexity of the phenotypic heterogeneity of cases with coexisting asthma and COPD searching for new genetic and molecular biomarkers appears crucial to identify homogeneous subgroups of patients in terms of etiologic mechanisms and response to treatment. This review presents the inflammatory, immunological, genetic and structural processes involved in asthma and COPD and highlights the nature of the link between these two conditions.