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

Background/Objectives: Cough variant asthma (CVA) is characterized by nonspecific 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 using the methacholine challenge test (MCT). Methods: In CVA-suspected patients, a bronchodilation test (BDT), an MCT with spirometry, and body plethysmography were performed. The MCT was considered positive if there was a 20% decrease in forced expiratory volume in 1 s from the baseline value (PC₂₀FEV₁) or a 40% reduction in specific conductance (PC₄₀sGaw) after inhaling methacholine of 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 the response to treatment. Results: AHR was diagnosed in 83.5% (91/109) of patients by either a BDT, PC₂₀FEV₁, or PC₄₀sGaw. After one year of follow-up, asthma was confirmed in 76 patients. The sensitivities of the BDT, PC₂₀FEV₁, and PC₄₀sGaw were 25%, 64%, and 97%, respectively. The specificities of the BDT, PC₂₀FEV₁ and PC₄₀sGaw were 94%, 88%, and 67%, respectively. The sensitivities for a PC₄₅sGaw and PC₅₀sGaw were 88% and 63%, and the specificities were 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 found at a PC₄₅sGaw.