The values of fractional exhaled nitric oxide in the diagnosis and treatment of chronic cough

Abstract

To evaluate the values of fractional exhaled nitric oxide (FENO) in the diagnosis and treatment of chronic cough. Based on the protocol from The Chinese Respiratory Society guidelines for management of cough, 75 consecutive subjects with chronic cough and normal chest radiographs were recruited from the outpatient clinic of the Department of Respiratory Diseases in China-Japan Friendship Hospital from January to June 2010. All the patients accepted FENO tests, sputum cell counts, pulmonary function tests, bronchial hyperresponsiveness (BHR), serum IgE, cough symptom scores and Leicester cough Questionnaire (LCQ) before and after treatment of 4 weeks. The final diagnosis of the subjects included 29 with cough variant asthma (CVA), 19 with eosinophilic bronchitis (EB) and 27 with other causes (Others). FENO levels in CVA (58 ± 26) ppb were significantly higher than those in EB (36 ± 18) ppb and Others (20 ± 7) ppb, and the FENO levels in EB were higher than Others (F = 28.2, P < 0.01). FENO levels showed significant correlations with sputum eosinophils, BHR, cough symptom scores, non-specific IgE, and LCQ scores. The mean baseline FENO level of the subjects whose coughs were relieved after inhaled corticosteroid therapy was (63 ± 42) ppb, higher than those of the non-responders (28 ± 13) ppb (t = 3.91, P < 0.01). There were significant correlations between the percentage of FENO decrease and the percentage of sputum eosinophil decrease or the cough symptom score decrease. FENO could be used as a inflammation marker of chronic cough because of its good correlation with sputum eosinophils, AHR, atopy, and cough symptoms. FENO also has a potential to predict the response of anti-inflammatory therapy because FENO decrease is correlated with the decrease of eosinophilic inflammation and improvement of cough symptoms.