Prevalence of bronchial reactivity to inhaled methacholine in New Zealand children MALCOLM

The prevalence of bronchial hyperreactivity to inhaled methacholine and of a clinical history of symptoms of asthma was determined in a birth cohort of9 year old New Zealand children. A history of current or previous recurrent wheezing was obtained in 220 of 815 children. Of 800 who had spirometric tests, 27 (3.4%) had resting airflow obstruction (FEV,/FVC < 75%). Methacholine challenge was undertaken without problem in 766 children, the abbreviated protocol being based on five breaths and four concentrations. A fall in FEV, of more than 20% was observed in 176 children (23% of challenges, 22% of the full cohort) after inhalation of methacholine in concentrations of up to 25 mg/ml. The prevalence of bronchial reactivity in children with symptoms was related to the frequency of wheezing episodes in the last year, and the degree of reactivity to the interval since the last episode. Sixty four children (8.0%) with no history of wheeze or recurrent dry cough were, however, also responsive to methacholine 25 mg/ml or less, while 35% of children with current or previous wheezing did not respond to any dose of methacholine. Bronchial challenge by methacholine inhalation was not sufficiently sensitive or specific to be useful as a major criterion for the diagnosis of asthma in epidemiological studies. The occurrence of airway reactivity in children without symptoms of asthma, however, raises the possibility that adult onset asthma and the development of airways obstruction in some subjects with chronic bronchitis could have origins in childhood. Asthma, although one of the most common diseases of childhood, is underdiagnosed and undertreated.'`3 The prevalence of childhood asthma is difficult to determine with certainty; estimates in New Zealand have ranged from 5% to 25%.' 4 7 We have previously reported a high prevalence of a history of wheezing in 7 year old children.' Our results were in keeping with Australian findings that 11-12% of children have clinically important wheezing in the first 7-10 years of life, and that a further 20% may have mild or trivial wheezing not labelled as asthma.8 9 Some of the variation in reported prevalence is attributable to differing interpretations of a history of wheezing, and the demonstration of bronchial reacAddress for reprint requests: Dr MR Sears, Department of Medicine, University of Otago Medical School, PO Box 913, Dunedin, New Zealand. Accepted 14 October 1985 tivity has been suggested as the ultimate standard for the diagnosis of asthma.'1' Non-specific bronchial reactivity to methacholine and histamine and to exercise has been well documented in subjects with symptomatic asthma,'2 17 methacholine challenge giving similar results to histamine challenge'5 and being more sensitive than exercise challenge.'6 '7 Few epidemiological studies using these techniques for the detection of asthma have been published.6 8 Lee et al8 found that one third of 7 year old British children with recurrent wheezing did not respond to histamine inhalation challenge, while one third of a control group of 100 symptomless children did react in some instances to very low concentrations of histamine. As part of a longitudinal multidisciplinary study of a birth cohort of New Zealand children now aged 9 years, we sought to determine the prevalence of bronchial hyperreactivity to inhaled methacholine and to assess the value of this challenge in determining the prevalence of asthma in childhood. 283 group.bmj.com on July 6, 2017 Published by http://thorax.bmj.com/ Downloaded from