Characteristics and Follow-Up of Bronchial Hyperresponsiveness in Cough Variant Asthma

Kim, Jeong Ho; Shim, Jung Yeon; Hong, Soo Jong

Abstract

PURPOSE
Cough variant asthma is characterized as a persistent, nonproductive cough with minimal or no wheezing and dyspnea. Cough variant asthma can be overlooked or misdiagnosed because it is a common problem amongst all ages that frequently is unrecognized. The patho-physiology of cough variant asthma is still unclear.
METHODS
To characterize the pathophysiological abnormalities of cough variant asthma, bronchial provocation tests with methacholine using stepwise doubling concentration technique were performed to the 20 patients of classic asthma and cough variant asthma. To evaluate the changes of bronchial hyperresponsiveness in cough variant asthma, follow-up bronchial provocation tests with methacholine were performed to the 9 patients of cough variant asthma. The concentration of methacholine and the severity of airway obstruction when wheezing and coughing were first detected were compared between classic asthma and cough variant asthma.
RESULTS
The PC20 (concentration of methacholine when decreased FEV1 20%), PCW (concentration of methacholine causing wheezing), PCC (concentration of methacholine causing coughing), delta FEV1 (FEV1% change from control), PCW/PC20 ratio, and PCC/PC20 ratio were not different significantly between classic asthma and cough variant asthma. There was a good correlation between the PCW and the PC20. The number of cough variant asthma who couldn't be heard wheezing sound during the provocation test were more significantly than that of classic asthma. Nine patients of cough variant asthma were followed for 1 year, their cough was improved and the PC20 of methacholine test was increased at 1 year later.
CONCLUSIONS
This data indicates that pathogenesis of cough variant asthma may be associated with a higher wheezing threshold and their bronchial hyperresponsiveness is much improved during the follow-up period.