The Methacholine Inhalational Challenge (MIC) in the Diagnosis of Bronchial Asthma

Although wheezing is usually symptomatic of asthma, it is not always present in asthmatics. Furthermore, when present in a person, wheezing may be symptomatic of some disease other than asthma. Therefore, we have used an inhalational challenge by the drug methacholine chloride to demonstrate the symptoms of persistent airway hyper-reactivity and bronchoconstriction in suspected asthmatics who do not manifest all the classic symptoms of the disease. We administer the drug by aerosolization, using the dose-unit concept to standardize dosage. For various time periods before the methacholine inhalational challenge (MIC) is performed, medications that block the response to methacholine must be withdrawn, and tobacco, chocolate, cola drinks, exercise, and cold air must be avoided to prevent a false negative result. Although specificity depends on the prior ruling out of certain other disease states, we have found the MIC to be a sensitive, easily performed, safe, and inexpensive diagnostic test for suspected bronchial asthma.