The Value of Body Plethysmography (sGaw) in the Assessment of Airway Hyperreactivity in Cough Variant Asthma

Background:  The cough variant asthma (CVA) is characterized by non-specific symptoms and normal spirometric values, which makes diagnosis challenging. To diagnose CVA it is necessary to document airway hyperreactivity (AHR). The aim of our study was to evaluate the diagnostic value of body plethysmography in the assessment of AHR by methacholine challenge test (MCT). Methods:  In CVA-suspected patients, a bronchodilation test (BDT), MCT with spirometry, and body plethysmography were performed. MCT was considered positive if there was a 20% decrease in forced expiratory volume in 1 second from the baseline value (PC20FEV1) or a 40% reduction in specific conductance (PC40sGaw) after inhaling methacholine concentration < 8 mg/mL. Sensitivity and specificity were generated for different cut off points of sGaw (PC40sGaw, PC45sGaw, PC50sGaw). Anti-asthma treatment was started for those with proven AHR. The diagnosis of asthma was made after one year of follow-up based on response to treatment. Results:  AHR was diagnosed in 83.5% (91/109) of patients by either BDT, PC20FEV1, or PC40sGaw. After one year of follow-up asthma was confirmed in 76 patients. The sensitivity of BDT, PC20FEV1, and PC40sGaw was 25%, 64%, and 97%, respectively. The specificity of BDT, PC20FEV1 and PC40sGaw was 94%, 88%, and 67%, respectively. The sensitivity for PC45sGaw and PC50sGaw was 88% and 63%, and the specificity was 82% and 91%, respectively. Conclusions:  Body plethysmography is a valuable tool in the assessment of AHR in CVA, with the best sensitivity-to-specificity ratio for PC45sGaw.