Asthma

Productinformatie

Asthma ìs one of the commonest disorders encountered in clinical medicine. The prevalence, pathogenesis, and management of asthma have been extensively studied, but the fundamental cause of asthma and the factors inducing and inciting airway inflammation are still unclear; the optimum methods of prevention of disease or control of ìts manifestations have yet to be established; and the international differences in morbidity and increases ìn mortality have become subjects of intense investigation and debate.

Asthma defies precise definition, despite several carefully worded statements? Perhaps the most concise and useful description of asthma is ‘variable airflow obstruction’. The diagnosis is made by recognition of a pattern of one or more characteristic s\mptoms including wheeze, cough, chest tightness and dyspnoea, and is best confirmed by evidence of variable or reversible airflow obstruction accompanying symptoms.” In children, asthma causing nocturnal or post-exercise cough may be misdiagnosed as bronchitis or infection.+® Increased responsiveness of the airways to non-allergic stimuli usually accompanies asthma symptoms® but is not synonymous with asthma. Airway hyperresponsiveness (AHR) is absent in some subjects with other clear evidence of asthma, and may be variably present in some children and adults without significant respiratory symptoms;’=ì! AHR is not sufficiently sensitive or specific for epidemiological purposes. Asthma is characterized by inflammation,'? but present methods for detecting airway inflammation are not suitable for community studies. Evidence of variable or reversible airflow obstruction (a 20% increase in forced exhaled volume in ls (FEV;) or peak expiratory flow rate (PEFR) occurring spontaneously or with treatment!$ is helpful if present. However, asthmatics who smoke, or work in highly ASl HMA BASIC MECHANISMS AND CLINICAL MANAGEMENT (2nd Edn) Copyright © 1992 Academic Press Limited ISBN 0-12-079026-2 ALL rights of reproductton an any form reserved

MR. Sean polluted atmospheres, may develop less reversible discase, and some asthmatics develop irreversible disease despite being lifetime non-smokers,* A carefully constructed ques. tionnaire is presently the most reliable tool for detecting current asthma in epidemiolog;. cal surveys, but is less reliable for establishing cumulative prevalence rates for which longitudinal studies provide more accurate data.

ASTHMA IN CHILDREN

Between 1.6 and 20.5% of children in the United Kingdom,°®!5* Canada! he United States, 6-2 Australia,”21-23 New Zealand,2? and Scandinavia® ® have significant recurrent respiratory symptoms suggesting asthma (Table 1.1). The variations in questions asked, age groups studied, and local factors may all affect comparability of responses; a uniform approach is yet to be used to enable detection of true differences between countries.

The prevalence of wheezing in childhood has probably increased over the last decade;®! however, differences in methodology, definitions, and use of the label ‘asthma’ have exaggerated any true increase in prevatence.5?:5 fn Australia In 1969, 19.1% of J-vearold children had had recurrent episodes of wheezing;®* in New Zealand in 1973, 23% af Y-vearvold children had a history of one or more attacks of wheezing,®® while in 1981-82 18,1% had three or more wheering episodes in a year.?° In these and other studies, parents of half to two=thirds of the children reporting wheeze denied their child had ‘asthma’; hence a change in use of that label in subsequent years could greatly alter the prevalence of reported asthma with little change in the burden of disease. Burney «f el. und an increase in prevalence of asthma for English children of both sexes between 1973 and 1986;°! however, the increase in prevalence of wheeze was much less and significant only in girls.

In the United States, however, reported prevalence among 6-1 1-year-old children increased significantly from 4.8 to 7,6% between the first (197174) and second (197680) Natìonal Health and Nutrition Examination Surveys. '° In each of these surveys, ‘asthma’ included recurrent wheezing not associated with colds as well as physiciandiagnosed asthma. The increase in prevalence cannot therefore be explained by a greater use of the label ‘asthma’, and is probably real. Similarly in Finland, the increase in asthma detected at medical examination in army conscripts rose from 0.08% ín 1961 to 0.29% ìn 1966 and then 20-fold to 1.79% in 1989.,% It seems unlikely that a change of this proportion relates to diagnostic fashion, as this would mean 95% of cases of asthma were undiagnosed before 1966.

Substantìal increases in hospital admissions for asthma in children in many countries suggest that the prevalence of severe asthma has increased.*-5° The rate of hospitalizaton for United States children under 15 years with asthma increased at least 145% between 1970 and 1984.“ In England, admissions increased 167% in 5-14-year-olds over a period of 8 years.*! The increase in hospital admissions for asthma has occurred despite falling admission rates for other respiratory conditions, and a considerable increase in the use of antiasthmatic medications,*? and is in part due to a doubling of the re-admission rate.*2** In one New Zealand pediatric unit, admissions rose dramatically from 21 in 1965 to 186 in 1975 and 609 in 1985, while the severity on admission (based on wheezing, pulse rate and accessory muscle use) also increased considerably in the latter 10 years.* These facts all suggest that asthma has increased in severity, although there is some evidence of increased self-referral to hospital especially for nebulizer treatments for children.

Studies of the prevalence of diagnosed asthma in children have usually found a male preponderance?®*? which decreases with increasing age.”*® Male predominance may relate to a greater degree of bronchial lability and not to a greater prevalence of atopy in males,*® although an Italian study found atopy was related to male sex.°® In Boston children, the M:F ratio for ‘asthma’ was 1.8:1, but for “recurrent wheeze most days or nights’ was 1:1, suggesting a sex-related diagnostic bias in use of the label ‘asthma’!