Bronchial hyperreactivity to methacholine in atopic versus nonatopic asthmatic schoolchildren and preschoolers.

BACKGROUND: Atopy and bronchial hyperreactivity are factors related to severe and unremitting asthma of childhood; however, the prevalence of these factors could be different according to age of the child.

OBJECTIVE: To determine if methacholine bronchial hyperreactivity (BHR) differs between atopic and nonatopic preschoolers and schoolchildren with mild-moderate asthma.

METHODS: Data obtained from 340 children with diagnosis of asthma or recurrent wheezing, matched by atopic conditions (positive or negative skin prick test) and age, and who underwent a methacholine bronchial challenge test (by spirometry in schoolchildren and by transcutaneous oxygen pressure [TcP(O₂)] in preschoolers) were reviewed.

RESULTS: Among 136 schoolchildren (9.07 ± 2.5 years), the prevalence of positive BHR was significantly higher among atopics than nonatopics (75% versus 48.5%, p = .001, respectively), even after controlling for gender and nutritional status (adjusted odds ratio [aOR] = 3.2129, 95% confidence interval [CI]: 1.5-6.8; p = .002). In addition, atopic schoolchildren had lower PC(20) and required a lower threshold dose of methacholine to induce a reaction (0.53 versus 0.82 mg/ml, p = .055 and .5 versus 1 mg/ml, p = .02, respectively) than nonatopics. Nevertheless, basal and predicted forced expiratory volume in one second (FEV₁) were similar between groups. In contrast, among 204 preschoolers (4.74 ± 1.1 years), there were no differences in the prevalence of positive BHR between atopics and nonatopics (74.5% versus 72.5%, p = .75, respectively). Furthermore, basal TcP(O₂), a higher fall of TcP(O₂) and lower threshold doses of methacholine required for induction as measured by TcP(O₂) were similar between the atopic and nonatopic preschoolers.

CONCLUSIONS: Atopic asthmatic schoolchildren have greater hyperresponsiveness to methacholine than nonatopics (only among those with normal nutritional status). However, atopic and nonatopic asthmatic preschoolers have similar hyperresponsiveness to methacholine. Therefore, factors different from atopy may be responsible for wheeze in younger children.