Eosinophilic bronchitis presents with chronic cough and sputum eosinophilia, but without the abnormalities of airway function seen in asthma. It is important to know how commonly eosinophilic bronchitis causes cough, since in contrast to cough in patients without sputum eosinophilia, the cough responds to inhaled corticosteroids.

 A very recent investigatation (2005) of patients referred over a 2-yr period with chronic cough, using a well-established protocol with the addition of induced sputum in selected cases showed that eosinophilic bronchitis was diagnosed if patients had no symptoms suggesting variable airflow obstruction, and had normal spirometric values, normal peak expiratory flow variability, no airway hyperresponsiveness (provocative concentration of methacholine producing a 20% decrease in FEV(1) ([PC(20)] > 8 mg/ml), and sputum eosinophilia (> 3%). Ninety-one patients with chronic cough were identified among 856 referrals. The primary diagnosis was eosinophilic bronchitis in 12 patients, rhinitis in 20, asthma in 16, post-viral-infection status in 12, and gastroesophageal reflux in seven. In a further 18 patients a diagnosis was established. The cause of chronic cough remained unexplained in six patients. In all 12 patients with eosinophilic bronchitis, the cough improved after treatment with inhaled budesonide 400 micrograms twice daily, and in eight of these patients who had a follow-up sputum analysis, the eosinophil count decreased significantly, from 16.8% to 1.6%. We conclude that eosinophilic bronchitis is a common cause of chronic cough, and that sputum induction is important in the investigation of cough.

 So background Eosinophilic bronchitis is an important cause of chronic cough. Treatment with inhaled corticosteroids is associated with a short-term improvement in cough and reduced sputum eosinophil count but the long-term outcome is uncertain. Objective To determine the long-term outcome in patients diagnosed with and treated for eosinophilic bronchitis. In another recent longitudinal study of symptoms, eosinophilic airway inflammation, spirometry and airway hyper-responsiveness in all patients diagnosed with eosinophilic bronchitis over 7 years. So the study identified 52 patients with eosinophilic bronchitis and longitudinal data of greater than 1 year (mean 3.1 years) was available in 32 patients, all of whom were treated with inhaled steroids. Three (9%) patients developed symptoms consistent with asthma and a methacholine PC(20)<8 mg/mL on one or more occasion. Five (16%) patients developed fixed airflow obstruction defined by a persistent post-bronchodilator forced expiratory volume in 1 s (FEV(1))/forced vital capacity <70%. One (3%) patient had complete resolution of symptoms and eosinophilic airway inflammation off treatment. The remaining patients had ongoing eosinophilic airway inflammation and/or continuing symptoms. Multiple linear regression identified smoking, female gender and area under the curve of sputum eosinophil count over time as the most important predictors of decline in FEV(1). With the conclusion that the most common outcome in eosinophilic bronchitis is continuing disease and complete resolution is rare. Asthma and fixed airflow obstruction developed in relatively few patients. The most important factors associated with a more rapid decline in FEV(1) were female gender, smoking and prolonged eosinophilic airway inflammation.

 Recent evidence suggests that the differences in functional association are related to differences in localization of mast cells in airway wall, with airway smooth muscle infiltration occurring in asthma and epithelial infiltration in eosinophilic bronchitis. Diagnosis is usually made with induced sputum analysis after exclusion of other causes for chronic cough on clinical, radiological and lung function assessment. The cough responds well to inhaled corticosteroids but dose and duration of treatment remain unclear. Little is known about the natural history of this condition. However, some patients with COPD without a history of previous asthma have sputum eosinophilia, so one possibility is that some cases of eosinophilic bronchitis may develop fixed airflow obstruction. Further study of this interesting condition will increase our understanding of airway inflammation and airway responsiveness, leading to novel targets for therapeutics for both eosinophilic bronchitis and asthma.

The recent development of noninvasive techniques to measure airway inflammation has led to the recognition of eosinophilic bronchitis, a condition characterized by a sputum eosinophilia identical to that seen in asthma, but without any of the functional abnormalities associated with asthma. The condition is interesting for a number of reasons. Firstly, eosinophilic bronchitis is a common cause of chronic cough, which is important to recognize as it responds well to corticosteroids. However, recognition is not straightforward because it requires assessment of airway inflammation. Secondly, the natural history of eosinophilic bronchitis is uncertain. Some patients with chronic obstructive pulmonary disease without a history of previous asthma have sputum eosinophilia, thus one possibility is that eosinophilic bronchitis may develop into fixed airflow obstruction. Finally, the difference in the association of eosinophilic airway inflammation to airway dysfunction between eosinophilic bronchitis and asthma is of interest as it is possible that it reflects important differences in the nature or site of the airway inflammation. Further study of this interesting condition may shed light on the relationship between airway inflammation and airway responsiveness, leading to a greater understanding of both eosinophilic bronchitis and asthma.

Barbara Colacchia

May 2005

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