Methacholine challenge in detecting bronchial hyperreactivity in children

Background: The diagnosis of bronchial asthma is usually apparent from presenting signs and symptoms. Occasionally, however, there is uncertainty and clinicians may use bronchial hyperreactivity, determined by methacholine inhalation challenge, as a diagnostic aid. Children are known to be more sensitive to methacholine than adults doses used in adults will result in false-positive responses. Objective: To determine the optimal methacholine inhalation challenge dose providing sensitive and specific discrimination between bronchial hyperreactivity and normal reactivity in children. A second objective was to determine whether gender, baseline spirometry values, race, tobacco smoke exposure, and family income affect methacholine response. Method: In 71 children aged 7 to 15 years airway hyperreactivity was determined by history and physical findings. Methacholine challenge was performed using an established protocol. Sensitivity and specificity of the challenge were calculated at 50, 100, and 225 breath units (BU). Results: Sensitivity was similar at 100 and 225 BU (54% and 58% respectively) while at 50 BUs sensitivity was only 33%. Specificity was 83% at 50 BU, 74% at 100 BU, and 49% at 225 BU. At 100 BU the best combination of sensitivity and specificity was achieved. Limitations of methacholine challenge were apparent since the positive predictive value did not exceed 10% at any dose; the negative predictive value exceeded 95% at all doses. Methacholine reactivity was less in female children, and airway reactivity was inversely correlated with several spirometry values. There were no significant relationships between race, smoke exposure and family income. Conclusion: Bronchial asthma is best diagnosed by history and physical findings, reserving methacholine challenge for difficult diagnostic situations. When used, the methacholine challenge in children should progress incrementally up to 100 BU. Doses above this will frequently give false positive results. Young female children are less responsive to methacholine provocation than males, possibly offering insight into the lower prevalence of asthma in girls in this age group.