COUGH VARIANT ASTHMA IS ASSOCIATED WITH A HIGHER WHEEZING THRESHOLD THAN CLASSIC ASTHMA

Cough variant asthma is an occult form of asthma in which the only sig n or symptom is chronic cough. It is a common problem amongst all ages that frequently goes unrecognized, leading to underdiagnosis and unde rtreatment. To characterize the pathophysiological abnormalities in th ese patients, we performed bronchial provocation tests with methacholi ne using the stepwise doubling concentration technique, and measured t he concentration of methacholine and the severity of airway obstructio n when wheezing was first detected. Airway hyperresponsiveness, define d as PC20 in the cough variant asthma group was not significantly diff erent from that of classic asthma. There was a good correlation betwee n the PCW (the concentration of methacholine causing wheezing) and the PC20 with the PCW values higher than PC20 values in both groups. Howe ver, in the cough variant asthma group, the PCW: PC20 ratio was greate r than that of the classic asthma group. Furthermore, the mean % fall in FEV1 at which wheezing was first detected in the former group was s ignificantly larger than that of the latter group. The results indicat ed that the mechanism for the manifestation of cough without wheeze in the cough variant asthma may be a higher wheezing threshold, i.e. whe ezing becomes audible at the greater degree of airway obstruction than classic asthma. They suggested that patients with cough variant asthm a may represent a subset of asthmatic subjects whose airways are less able to produce a wheeze.