Eosinophils, bronchitis and asthma: pathogenesis of cough and airflow obstruction

Eosinophilic airway inflammation is commonly observed in chronic cough in patients with asthma and non-asthmatic eosinophilic bronchitis. Indeed asthma and non-asthmatic eosinophilic bronchitis are amongst the commonest causes of chronic cough accounting for about 25 and 10% of cases respectively. In most cases the trigger that causes the cough is uncertain; however removal of potential triggers is important to consider in particular with respect to occupational exposure to known sensitizers. In both conditions the cough improves subjectively and objectively following treatment with corticosteroids. This improvement is associated with the presence of an airway eosinophilia, but whether eosinophilic inflammation is the cause of cough or an epiphenomenon is uncertain. The success of anti-IL5 to reduce eosinophilic inflammation and asthma exacerbations contrasts with the lack of efficacy to modify cough in asthma and therefore challenges a causal association. Both asthma and non-asthmatic eosinophilic bronchitis can lead onto airway remodeling and result in persistent airflow obstruction. However, response to corticosteroid therapy in both conditions is generally very good and the limited long term data available suggests that both usually have a benign course. Interestingly, improvement in airway remodeling in response to anti-IL5 observed using CT imaging and analysis of sub-epithelial matrix deposition does suggest that the eosinophil may play a causal role in airway remodeling.