Cough, dyspnea, and chest pain are symptoms common to many cardiopulmonary diseases. A comprehensive evaluation, including a history, physical examination, ECG, chest roentgenogram, and pulmonary function studies, will often yield a specific diagnosis. However, when these symptoms are intermittent, as they often are in patients with bronchial asthma, the diagnosis may not be apparent. If asthma is thought to be a diagnostic possibility, a bronchial inhalation challenge should be used to demonstrate bronchial hyperreactivity, the hallmark of asthma. The methacholine chloride inhalation challenge is a simple and useful laboratory test to diagnose bronchial hyperreactivity. We describe eight patients with a variety of clinical symptoms to demonstrate the usefulness of this test. Patients with unexplained respiratory symptoms should be considered for bronchial inhalation challenge before proceeding to more invasive diagnostic procedures.
Myers JR, Corrao WM, Braman SS. Clinical Applicability of a Methacholine Inhalational Challenge. JAMA. 1981;246(3):225-229. doi:10.1001/jama.1981.03320030017019