Gastro-oesophageal reflux, eosinophilic airway inflammation and chronic cough

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.

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.

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%).

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.