Asthma-like symptoms induced by the methacholine challenge test: do they predict a negative-to-positive switch in the test result?—case report

The methacholine challenge test (MCT) is primarily indicated to help determine if current respiratory symptoms may be due to asthma or not (1,2). A positive test is generally defined as the provocative concentration (or dose) of methacholine causing a 20% fall in forced expiratory volume in one second (PC20FEV1) without consideration of the symptoms that may occur during the test, such as dyspnoea, cough, chest tightness and wheezing (2).