Features of cough variant asthma and classic asthma during methacholine-induced brochoconstriction: a cross-sectional study

We cross-sectionally examined the degrees of airway sensitivity, the point where resistance started to increase, and reactivity, the slope of the methacholine-resistance curve, and the appearance of cough and wheezes in steroid-na？ve adult patients with classic asthma (n = 58) or CVA (n = 55) while they were continuously inhaling methacholine during simultaneous measurement of respiratory resistance.Patients with CVA were less sensitive and less reactive to inhaled methacholine and wheezed less frequently but coughed more frequently during methacholine-induced bronchoconstriction than did patients with classic asthma. Multivariate analysis revealed that airway hypersensitivity and lower baseline FEV1/FVC were associated with the appearance of wheezes, whereas a diagnosis of CVA was associated with coughing.There are mechanistic and phenotypic differences between CVA and classic asthma during methacholine inhalation. Frequent coughing during bronchoconstriction may be a distinctive feature of CVA.Patients with cough variant asthma (CVA) present with a chronic cough as the sole symptom that responds to bronchodilator treatment and show airway hyperresponsiveness (AHR). CVA, one of the most common causes of chronic cough [1-4], is considered a precursor [5-9] and a variant form of classic asthma with typical symptoms of wheezing and dyspnea [5]. Several studies have examined mechanistic differences between CVA and classic asthma. Airway sensitivity, a component of airway responsiveness that is defined as the inflection point where respiratory resistance (Rrs) starts to increase, did not differ between patients with CVA and those with classic asthma in a few small studies [10,11]. In contrast, airway reactivity, another component of airway responsiveness expressed as the slope of the dose-response curve, is attenuated in children with CVA as compared with those with classic asthma [12]. In adults with CVA, however, no study has separately examined airway sensitivity and