Use of Exhaled Nitric Oxide in Predicting Response to Inhaled Corticosteroids for Chronic Cough

OBJECTIVE To evaluate our experience with patients who presented with chronic cough and how exhaled nitric oxide predicted response to inhaled corticosteroid (ICS) therapy. PATIENTS AND METHODS This retrospective observational study of 114 patients evaluated for chronic cough with measured exhaled nitric oxide and methacholine challenge testing was conducted from December 1, 2004, through November 30, 2005. Clinical records were extracted. Patients with no documented follow-up were contacted by telephone and administered a questionnaire. RESULTS In 64 patients, ICS therapy was started or the current ICS dose increased. Forty-one patients had elevated exhaled nitric oxide levels (defined as ≥35 ppb), 36 (88%) of whom had significant improvement in their chronic cough (likelihood ratio of a positive response, 4.9; 95% confidence interval, 2.2-10.9). Twenty-three patients with exhaled nitric oxide levels in the reference range were also prescribed ICS, and only 2 had cough improvement (likelihood ratio of a negative response, 0.07; 95% confidence interval, 0.02-0.25). Patients had documented follow-up that ranged from 4 weeks to 16 months. A cutoff of 38 ppb was found to best differentiate ICS responders and nonresponders. CONCLUSION Measurement of exhaled nitric oxide accurately predicted response to ICS therapy for chronic cough. Patients with a positive exhaled nitric oxide test result had a strong likelihood of response to ICS, whereas a negative exhaled nitric oxide test result indicated an unlikely response to ICS. This finding may potentially have an impact on how patients with chronic cough are evaluated and treated.