Increased concentrations of exhaled nitric oxide (ENO) are identified predominantly in subjects with chronic cough due to conditions that habitually respond well to therapy with inhaled corticosteroids (ICSs). The aim of this study was to assess the usefulness of ENO in predicting the response to ICS therapy in subjects with chronic cough and to determine the relationship between either methacholine or adenosine 5′-monophosphate (AMP) responsiveness and the response to ICS therapy.
A total of 43 patients with chronic cough were studied. During the baseline period, ENO measurement, spirometry, and concentration-response studies with both methacholine and AMP were performed. For the next 4 weeks, the patients were treated with inhaled fluticasone propionate, 100 μg twice daily. At baseline (1 week) and during the 4-week treatment period, patients twice daily completed entries in a diary, in which they recorded daytime and nighttime cough symptom scores.
Nineteen patients (44%) responded well to fluticasone therapy. The receiver operating characteristic curve analysis showed that the accuracy of identifying the response to ICS therapy for ENO at baseline was poor. The sensitivity and specificity of ENO for predicting the response to ICS therapy, using 20 parts per billion as the ENO cutoff point, were 53% and 63%, respectively. Differences in both prevalence and degree of airway responsiveness to either methacholine or AMP between fluticasone-responsive subjects and nonresponsive subjects were also not significant.
Although a significant proportion of subjects with chronic cough respond well to ICS therapy, these patients cannot be identified by ENO levels or AMP responsiveness at baseline.