Small airway dysfunction in patients with cough variant asthma: a retrospective cohort study

BACKGROUND: Cough variant asthma (CVA) is one of the special populations of asthma. The aim of the study was to compare small airways, the degree of bronchial hyperresponsiveness (BHR) and airway inflammatory subtypes between CVA and classic asthma (CA), and investigate the relationship between these markers to determine the accuracy as indicators of CVA. METHODS: A total of 825 asthmatic patients participated in the study and 614 were included. 614 patients underwent spirometry and a bronchial challenge with methacholine and 459 patients performed induction sputum cell test. RESULTS: The number of CVA patients showed less small airway dysfunction than those of CA patients (p < 0.005). The degree of small airways dysfunction was higher in the CA group compared with the CVA group (p < 0.001). Small airways dysfunction was severer in the eosinophilic airway inflammatory subtype compared with other subtypes (p < 0.05).The area under curve of MMEF, FEF(50) and FEF(75) (% predicted) was 0.615, 0.621, 0.606, respectively. 0.17mcg of PD(20) and 4.7% of sputum eosinophils was the best diagnostic value for CVA with an AUC of 0.582 and 0.575 (p = 0.001 and p = 0.005, respectively). CONCLUSIONS: The eosinophilic airway inflammatory subtype may be increased small airway dysfunction. The value of small airways, BHR and induction sputum cells in CVA prediction, which reflected significant, but not enough to be clinically useful.