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

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.

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.

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 FEF_50% 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), FEF_50% predicted (r=0.2522, P<0.001), and FEF_75% 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).

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.