Background: Eosinophilic inflammation of the airway is usually associated with airway hyper-responsiveness in bronchial asthma. However, there is a small group of patients which has the eosinophilic inflammation in the bronchial tree with normal spirometry and no evidence of airway hyper-responsiveness, which was named eosinophilic bronchitis. The objectives of this study are 1) to investigate the incidence of eosinophilic bronchitis in the chronic cough syndrome and 2) to evaluate the clinical features and course of eosinophilic bronchitis.
Methods: We evaluated 92 patients who had persistent cough for 3 weeks or longer. In addition to routine diagnostic protocol, we performed differential cell count of sputum. Eosinophilic bronchitis was diagnosed when the patient had normal spirometric values, normal peak expiratory flow variability, no airway hyper-responsiveness and sputum eosinophilia (> 3%).
Results: The causes of chronic cough were post-nasal drip in 33%, cough variant asthma in 16%, chronic bronchitis in 15% and eosinophilic bronchitis in 12% of the study subjects. Initial eosinophil percentage in the sputum of patients with eosinophilic bronchitis was 26.8 +/- 6.1% (3.8-63.7%). Treatment with inhaled steroid is related with a subjective improvement of cough severity and a significant decrease of sputum eosinophil percentage (from 29.1 +/- 8.3% to 7.4 +/- 3.3%). During the follow-up period, increase in sputum eosinophil percentage with aggravation of symptoms were found.
Conclusion: Eosinophilic bronchitis is one of the important cause of chronic cough. Assessment of airway inflammation by sputum examination is important in investigating the cause of chronic cough. Cough in eosinophilic bronchitis is effectively controlled by inhaled corticosteroid, but may follow a chronic course.