Symptom evaluation during the methacholine test: Does it add to the interpretation of the test results based on the PC20FEV1?

Abstract

Purpose: Conventionally, symptoms occurring during the methacholine test are not taken into account when interpreting the test results. We examined whether the evaluation of methacholine-induced symptoms (MIS) added to the test interpretation based on the PC20FEV1 by assessing their prevalence, their similarity with symptoms justifying referral and their relationship with airway responsiveness. Methods: Eighty-two patients with suspected asthma completed a questionnaire of symptoms and underwent bronchial challenge with methacholine. Based on MIS and airway responsiveness (responders = PC20FEV1 < 8 mg/mL), subjects were classified as asymptomatic non-responders (ANRs), asymptomatic responders (ARs), symptomatic non-responders (SNRs) and symptomatic responders (SRs). Airway responsiveness for all subjects, including non-responders (ie, fall in FEV1 < 20%), was assessed by the methacholine concentration response-slope (MCRS) obtained using all points of the curve. Results: ARs (n = 6) were poor-perceivers of bronchoconstriction. SNRs (n = 16) did not differ from SRs (n = 34) in any clinical parameter, including the proportion of subjects (∼80%) whose methacholine test reproduced symptoms justifying referral. In turn, SNRs differed significantly from ANRs (n = 26) by having lower baseline FEV1 (P =.005), more physician-diagnosed asthma (P