Small Airways Dysfunction and Bronchial Hyper-Responsiveness in Cough Variant Asthma

Background: Cough variant asthma (CVA) is one kind of atypical asthma. The study was to compare spirometric parameters of small airways and the degree of bronchial hyper-responsiveness (BHR) between CVA and classic asthma (CA), and examine the relationship between BHR and small airways to determine the accuracy of these markers as indicators of CVA. Methods: A total of 825 asthmatic patients were screened for the study, and 614 were included. All patients performed spirometry and underwent a bronchial challenge with methacholine. Results: The number of small airways dysfunctions in the CVA group was less than those of the CA group with MMEF% predicted (70% vs 80.91%, P=0.002) and FEF50% predicted (62.71% vs 73.5%, P=0.004). The degree of small airways dysfunction was less in the CVA group compared with the CA group (P<0.001). Significant positive correlations were observed between the FEV1 level below 20% of the baseline value (PD20) and MMEF% predicted (r=0.282, P<0.001), FEF50% predicted (r=0.2522, P<0.001), and FEF75% predicted (r=0.2504, P<0.001) in patients with CVA. The area under curve (AUC) of MMEF, FEF50, and FEF75 (% predicted) was 0.615, 0.621, and 0.606, respectively. In addition, 0.17 mcg of PD20 was the best diagnostic value for CVA, with an AUC of 0.582 (P=0.001). Conclusion: Small airway dysfunction is milder in CVA. The value of BHR combined with small airways in CVA prediction, which was significant, but not enough to be clinically useful.y