Gastro-oesophageal reflux, eosinophilic airway inflammation and chronic cough

Background and objective: Patients with eosinophilic airway inflammation (EAI) often show a therapeutic response to corticosteroids. Non-invasive methods of diagnosing EAI are potentially useful in guiding therapy, particularly in conditions such as chronic cough, for which corticosteroids may not be the first-line treatment. Methods: The value of exhaled nitric oxide (ENO) in the diagnosis of EAI was prospectively investigated in a cohort of 116 patients with chronic cough of varying aetiology. An optimum cut-off value was derived for differentiating between EAI and non-EAI causes of chronic cough. As the diagnosis was gastro-oesophageal reflux in 70 patients (60.3% of the total), the possible relationship between ENO and EAI in the presence or absence of reflux was subsequently investigated. Results: The optimum value of ENO for differentiating EAI (32% of patients) from non-EAI causes of cough was 33 parts per billion (sensitivity 60.5%, specificity 84.6%). In the subgroup of patients with reflux, ENO was highly specific for the diagnosis of EAI (sensitivity 66%, specificity 100%). Conversely, in the patients without reflux, ENO did not discriminate between cough due to EAI or other causes (sensitivity 100%, specificity 28.9%). Conclusions: These results suggest that the presence or absence of reflux should be taken into consideration when interpreting ENO measurements in the diagnosis of chronic cough associated with EAI. This study provided support for an association between gastro-oesophageal reflux and EAI and raised the possibility that when exhaled nitric oxide levels are high, concurrent treatment of both entities, rather than corticosteroid therapy for EAI alone, may be required to achieve satisfactory responses to treatment in patients with chronic cough. © 2011 Asian Pacific Society of Respirology