Long-term Outcome

Abstract

There are no studies that relate early childhood wheezing to school-age asthma, and relatively few cohort studies have examined the natural history of school-age asthma. Most studies have been conducted on hospitalized or hospital clinic patients, thus leading to possible bias in selection of more severely ill patients. Many were also retrospective in design, thus raising important questions about loss to follow-up. Almost no studies have incorporated a physiologic test of airway reactivity, although several have examined skin-test reactivity. No universally accepted definition of asthma was used in most of the investigations. Finally, no studies have concurrently examined all known main pediatric risk factors such as respiratory infection, active and passive cigarette smoking, and allergen sensitization and exposure and their relationship to the natural history of disease. Twoparticular areas in the natural history of early childhood asthma are poorly understood. First, the fate of wheezy infants and the factors predicting which of these children go on to develop school-age asthma is unclear. Second, we do not know whether early childhood factors such as symptoms, lung function, and airway responsiveness influence the natural history of school-age asthma, specifically maximal-attained FE~, and the presence of chronic symptoms in early adulthood (15-20 yr of age). Almost 40% of children wheeze in the first 3 yr of life, yet the predictors of who will continue to wheeze in later Childhood are unclear. Early childhood lower respiratory illness is a risk factor for later childhood asthma and lower levelsof FE~ (71). Early childhood lower respiratory illness may be a risk factor for adult chronic obstructive pulmonary disease (COPD) (4, 72, 73). Between 30 and 70% of school-age children with doctordiagnosed asthma can expect a marked improvement in their condition or to become symptom-free by early adulthood (72, 74-76). Significant disease will persist in approximately 30% of patients (77). School-age boys with asthma appear to have a better longterm (adult) prognosis than school-age girls (74-76, 78, 79). The incidence of school-age asthma is greater in males until puberty and increases in females after puberty (80, 81).Over 80% of school-age asthmatics have positive skin test reactivity (14, 74-79,82). Children of school age who have continuous respiratory symptoms will have lower levels of lung function and a worse prognosis, as measured by lower levels of pulmonary function (83-85). Airway reactivity in the absence of asthma is associated with differences in lung function growth in school-age children, specifically reductions in FEV2575 in both males and females, larger vital capacities in males, and reduced FE~ in females. Pulmonary function in school-age children with mild asthma has a high tracking correlation and is reasonably predictable. Tracking of lung function also occurs in early childhood (86-89). Available data suggest that adult doctor-diagnosed asthma is associated with an accelerated decline in lung function and, hence, the development of COPD (90-93). The presence of atopic dermatitis in school-age children is associated with more persistent symptoms of wheeze (74-76, 78, 79, 94-97). Wheezing only with respiratory illness is associated with improved lung function and reduced symptoms in early adulthood (71, 72, 98), though one risk factor for wheezing lower respiratory illnesses is low lung function soon after birth (12, 13, 52).