Pattern of Methacholine-Induced Bronchial Reactivity in Siblings of Asthmatic Subjects

Methacholine challenge tests can be used to establish the presence of bronchial reactivity, and thus provide supportive evidence for a clinical diagnosis of asthma. However, a significant number of pediatric patients may have positive challenge tests, yet not be asthmatic. We determined the degree of bronchial reactivity in a population of children who are siblings of asthmatics. Sixty-three nonasthmatic children, who were part of a Natural History of Asthma study, had a methacholine challenge, completed a respiratory questionnaire, and had skin tests. Thirty-nine of them responded to methacholine with at least a 20% fall in FEV₁; 18 had PD₂₀ values less than 200 breath units (bu). The atopic status of the subjects did not influence the degree of methacholine responsiveness. Nonasthmatic siblings of asthmatics had increased nonspecific bronchial reactivity but were not having symptoms of asthma.