Eosinophilic airway disorders

Diseases of the airway are common and make up a significant proportion of the respiratory physician's workload. The major contributors to this situation, such as asthma, chronic obstructive pulmonary disease (COPD), and chronic cough, all result from airway inflammation and often have an overlapping clinical picture, which in some instances makes accurate clinical diagnosis difficult. Asthma is a condition characterized by variable airflow obstruction, airway hyper-responsiveness, and airway inflammation, which is usually eosinophilic. However, the relationship between eosinophilic inflammation and asthma is complex, with only a weak correlation between the severity of airway inflammation and the markers of the severity of asthma, such as Pc20 and FEV1. Eosinophilic bronchitis is characterized by a chronic cough and sputum eosinophilia without airway hyper-responsiveness or variable airflow obstruction. The asthma phenotype is characterized by microlocalization of mast cells in the airway smooth muscle, emphasizing the importance of airway smooth muscle dysfunction in asthma. COPD has generally been considered to be a neutrophilic disease, in contrast to asthma. However, there is increasing evidence that a significant subgroup exists consisting of patients with stable COPD who have chronic airway eosinophilia with a more steroid-responsive disease. This article covers the role of eosinophils in the airway disorders asthma, COPD, and eosinophilic bronchitis.