Wheezing on maximal forced exhalation in the diagnosis of atypical asthma. Lack of sensitivity and specificity.

Abstract

To determine whether wheezing on maximal forced exhalation is a predictor of asthma in persons with normal or nearly normal baseline spirometry. Prospective study of patients referred for methacholine challenge testing. Pulmonary function laboratory at a hospital. Forty-four patients referred for methacholine challenge testing because of the clinical suspicion of cough variant or otherwise difficult to diagnose asthma, with normal or nearly normal baseline spirometry and without wheezing on routine lung auscultation during quiet breathing. We listened for wheezing on maximal forced exhalation. Wheezing was defined as a continuous sound with a musical quality. Methacholine challenge testing was done. The concentration of methacholine required to produce a 20% fall in baseline FEV1 (PC20) of less than 8 mg/mL was considered a positive test for asthma. Wheezing was present on maximal forced exhalation in 8 of 14 patients with a positive methacholine challenge test (sensitivity = 57%) and absent in 11 of 30 patients with a negative test (specificity = 37%). Furthermore, wheezing on maximal forced exhalation was present in 13 of 27 patients with a PC20 greater than 16 mg/mL and absent in 2 of 7 with a PC20 less than 4 mg/mL. Wheezing on maximal forced exhalation is neither sensitive nor specific for airway hyperreactivity.