Determinants of airway responsiveness to adenosine 5'-monophosphate in school-age children with asthma

Abstract

Airway responsiveness to adenosine 5'-monophosphate (AMP) is more specific than that to direct stimuli for asthma diagnosis and response to treatment, but is not detected in all patients with asthma. This study was planned to determine predictive factors for responsiveness to AMP in asthmatic children between 7-16 years old. We performed a retrospective analysis of data from 71 asthmatic children who were challenged by AMP in our department. All children were characterized by skin-prick and lung function tests and bronchial challenge with AMP. Data on simultaneous methacholine challenge tests were available for 46 children, 34 of whom were also challenged with a third stimulus, exercise. Potential demographic factors for responsiveness to AMP were assessed by logistic regression analysis within the study group. The proportion of school-age children with asthma responsive to AMP was 39.4%. The geometric mean provocative concentration of AMP causing a 20% decrease in forced expiratory volume in 1 sec (PC20AMP) was 20.50 mg/ml (range, 0.31-377 mg/ml). There were no significant differences either in response to methacholine below 16 mg/ml (P = 0.66) or in PC20 methacholine level (P = 0.075) when we compared AMP-responsive and -nonresponsive children. These two groups also did not differ with respect to their response to exercise challenge in subgroup analysis (P = 0.34). Among school-age children with asthma, allergic rhinitis (P = 0.004) and sensitizaton to grass mix (P = 0.001), cereal mix (P = 0.003), house dust mite (P = 0.024), and cat (P = 0.043) were found to be more frequent in AMP-responsive children than the others. There was no difference in lung function test parameters between children responsive to AMP and the others. Grass pollen sensitization was found to be the only independent predictive factor for determining AMP responsiveness in school-age children with asthma (odds ratio, 5.65; 95% confidence interval, 1.84-17.45; P = 0.003). In conclusion, atopic sensitization is the most important predictive factor for responsiveness to AMP in school-age children with asthma, as in adults.