ASTHMA MANAGEMENT IN CHILDREN

Asthma Management
The clinical management of asthma in children continues to evolve and was recently reviewed in this journal. Key aspects of management include accurate diagnosis and assessment of severity, initiation of appropriate maintenance therapy (with inhaled corticosteroids in most cases of persistent asthma), and education regarding management of asthma and proper use of meterdosed inhalers (MDI) with spacer devices. Attention to cultural competence and access to continuity of care are also necessary for optimal management of childhood asthma. Failures of asthma management generally result from improper assessment of asthma severity with undertreatment with maintenance medications, failure to use proper methods of medication delivery (e.g., use of spacers with MDIs), failure to treat comorbid disorders, such as allergic rhinitis, gastroesophageal reflux and sinusitis, and patient noncompliance due to beliefs, improper asthma education, or poor access to continuity of care. All pediatricians caring for children with asthma should be familiar with the national asthma guidelines. Patient education is critical for the success of asthma management in children.

Natural history
While we now are able to control asthma in most children with appropriate maintenance medications and education, preventative measures are needed. The results of several longitudinal studies have demonstrated the importance of childhood wheezing in the natural history of wheezing in adulthood. Further support is provided by a recent report of asthma outcomes among an unselected, population-based birth cohort of 1139 children born in Dunedin, New Zealand in a 1-year period between 1972 and 1973. Participants were evaluated repeatedly between 9 and 26 years of age by questionnaires regarding wheezing episodes and treatment, pulmonary function testing, bronchial provocation testing, and skin testing for environmental allergens. Among 613 participants with complete data at 26 years of age, 14.5% had wheezing that persisted from childhood to 26 years of age and 27.4% had childhood wheezing that went into remission. Of the patients experiencing remissions, 45.2% had relapse by 26 years of age. Risk factors for persistent and relapsing wheezing included dust mite sensitivity, airway hyper-responsiveness, female sex, smoking at 21 years of age, and earlier age of onset of wheezing. Impaired lung function appeared to develop during early childhood, with no significant further deterioration beyond 9 years of age. This study provides further support that the origins of persistent asthma are in the first years of life. Identification of those environmental exposures occurring during infancy and the early childhood years that lead to the development of asthma in genetically predisposed individuals must be identified to allow preventive measures. This remains an active area of investigation.

Breastfeeding and development of asthma
The role of breastfeeding in the development and progression of atopic disease has been controversial. Long-term benefits of breastfeeding in prevention of asthma have been questioned, including from analysis of data from the Dunedin, New Zealand study, which demonstrated that breast-feeding increased the long-term risk of developing asthma. Two recent studies demonstrated that breastfeeding, particularly for longer duration, appears to decrease the prevalence of wheezing during the first years of life, as has been demonstrated in several previous studies. Breastfeeding should be promoted for its many benefits. The factors that may lead to asthma in the long-term in breastfed infants is likely complex (including reduction in childhood infections) and those factors must be identified and addressed independently in preventive strategies.

Dietary supplements
Dietary supplements have also been suggested to alter the onset of atopic diseases. Administration of fish oil supplements to pregnant women with allergic disease reduced the incidence of childhood atopic disease. Serum antioxidants have also been shown to have a modest effect in reducing asthma risk. Most significantly, patients with exposure to passive tobacco smoke, as measured by serum cotinine levels, had a greater protective effect from elevated selenium levels in terms of asthma risk. Dietary supplementation with multivitamins during the first 6 months of life was associated with an increased risk of developing asthma among black children and is associated with increased risk of developing food allergies among exclusively formula-fed children. While these studies are interesting and may lead to methods for prevention, follow-up studies are necessary to clarify the results and evaluate long-term effects on multiple outcomes before being incorporated into our patient care strategies.

Endotoxin
Exposure to endotoxin during the first years of life has been associated with decreased risk of developing atopic diseases, including asthma. Further support is provided by a recent report from the Home Allergens and Asthma Study. Among 401 children in a birth cohort study, restricted to children with a family history of parental allergy, exposure to high levels of endotoxin in the first months of life was associated with a reduced risk of eczema during the first year of life. Elevated endotoxin in house dust is associated with pet ownership and farm animals and may explain the protective effects of these exposures that have been reported in several studies, although there are many aspects of the association that must be clarified. Since eczema is commonly the initial manifestation of the atopic march, interventions that reduce the risk of eczema may modify the course of the atopic march, which leads to asthma. Interventions designed to mimic these protective effects on the immune system are being developed and may play an important role in prevention.

Human metapneumovirus
Respiratory tract infections have been implicated in the pathogenesis of asthma. Roles in pathogenesis have included initiating onset of asthma, exacerbating existing asthma, or in some cases, preventing onset of asthma. Human metapneumovirus, a member of the Pneumovirinae subfamily that includes respiratory syncytial virus, was identified in 2001 as a new causative agent for acute respiratory infections. A recent analysis of nasal wash specimens for human metapneumovirus from a large cohort of children, observed prospectively from 1976 to 2001, demonstrated that, among 248 children with lower respiratory tract disease without identifiable infectious cause, the virus was identified in 49 children (20%). Thus, among the entire cohort of children with lower respiratory tract disease, human meta pneumovirus was identified as the likely causative agent in 12%. Clinical findings among the children infected with human meta pneumovirus included cough, coryza, rhinitis, and fever. Wheezing was identified in 52% of the patients. The mean age of infected children was 11.6 months; most cases occurred between December and April; and 2% required hospitalization. Human meta pneumovirus was associated with bronchiolitis in 59% of cases, pneumonia in 8% of cases, croup in 18% of cases, and asthma exacerbation in 14% of cases. The spectrum of illnesses associated with the newly identified virus is similar to respiratory syncytial virus. The role of the virus in the development and exacerbations of asthma must be studied to clarify possible roles.

Exercise limitations in children with asthma
Exercise/activity-induced bronchospasm is common in children and is the most common trigger for asthma exacerbations. Activity-induced symptoms have the potential to limit physical activity and all of the benefits associated with an active lifestyle.

One of the major goals of asthma management is to promote a normal level of physical activity without limitations in most cases, which depends on proper diagnosis and treatment with maintenance medications. Two reports over the past year have addressed factors that may limit activity in children with asthma.

In one study, telephone interviews using a structured survey were used to question parents of 137 children with asthma and 106 controls regarding activity level and frequency of physical activity, asthma severity and treatment, and caregiver beliefs about physical activity and asthma. All children were 6 to 12 years old and attended an urban primary care clinic in Baltimore. Parents of the children with asthma were found to report less physical activity. Factors associated with the decreased activity among asthmatics included increased disease severity and parental beliefs regarding physical activity and asthma.

A second study, from Canada, evaluated 64 children between the ages of 6 and 12 years old attending a summer asthma camp. Multiple factors were assessed, including questionnaires to assess activity, perceptions of activity limitations due to asthma, competence in physical activity, attitudes regarding physical activity, and medication use. Objective measures included height and weight, pulmonary function tests with bronchial provocation, and maximal aerobic power. Overall, maximum aerobic power was determined more by perception of level of fitness than by objective measures of asthma severity.

Overweight children had the greatest level of activity limitation and received more asthma medications, despite that their objective measures of asthma severity were similar to those who were not overweight. Appropriate treatment with maintenance medications need to be provided, as asthma fatalities during sports have been reported, with most not being on appropriate maintenance medications. However, all patients should be encouraged to participate in sports and factors limiting activity, including patient perceptions and effective management with maintenance medications and asthma action plans, should be carefully addressed during routine health visits.