Asthma is a heterogeneous syndrome with variable signs and symptoms among patients as well as significant variability in the individual patient over time. In young children, a practitioner must consider all possible causes, as not every child with reactive airway disease has asthma. In preschoolers, an important contributing genetic factor is atopy. Whether it is defined through serum immunoglobulin E antibody levels or by positive immediate hypersensitivity skin tests, atopy seems to confer an increased risk of getting asthma. Other factors, such as aeroallergen exposure, may exacerbate the process. Cockroaches, at least in the inner-city in the United States, seem to be a major factor for driving asthma morbidity and mortality. Other contributing risk factors are important, including a family history of asthma. Passive smoke exposure is a risk factor for wheezing in this age group as well.
Inflammation and airway remodeling, fundamental and interrelated pathogenic processes in asthma, occur at an early age. In very young children, wheezing may be a precursor of asthma or it could be a symptom of asthma requiring immediate treatment. Key markers of inflammation are nevertheless present early in life, emphasizing the importance of early intervention to prevent the airway remodeling that may contribute to loss of lung function over time.
Each of the authors of the articles in this supplement discusses different aspects of the pathophysiology, epidemiology, and treatment issues regarding early life events in the preschool-aged child.
In making a definitive diagnosis of asthma in young children, a physician faces many challenges. Although there are clinical and historical features consistent with asthma, identical features are present in many other diseases that must be ruled out before a definitive diagnosis is made. There is also no specific test for asthma. Dr Robert C. Strunk of the Division of Allergy and Pulmonary Medicine at Washington University School of Medicine discusses the dilemma of defining asthma in the preschool-aged child.
Dr Fernando D. Martinez of the University of Arizona at Tucson reviews the development of wheezing disorders and asthma in preschool-aged children. Data suggest that certain viruses, particularly respiratory syncytial virus, may play an important role in dictating which children who wheeze in the first 2 to 3 years of life are going to develop what would be called an asthmatic phenotype or asthma. Three phenotypes have been identified in children with asthma: transient wheezing, nonatopic wheezing of the toddler and preschool-aged child, and immunoglobulin E-mediated wheezing. Dr Martinez also explores the topic of early allergic sensitization, a risk factor for persistent asthma. Certain early exposures, including that to older siblings, day care attendees, pets, farm animals, and house-dust endotoxin, appear to decrease the risk for the development of persistent asthma. Some children, particularly those with severe persistent asthma, may experience progressive disease characterized by decreased pulmonary function and increased asthma symptomatology.
I discuss the role of inflammation in childhood asthma and other wheezing disorders. Some young children who develop asthma develop progressive loss of pulmonary function, at least over the first 6 years or so. Adult data suggest that, unless the disease is recognized early and treated appropriately, the loss of pulmonary function that occurs with asthma may proceed unimpeded, eventually leading to more chronic symptoms and chronic loss of pulmonary function.
Dr David B. Allen, of the University of Wisconsin Children’s Hospital in Madison, Wisconsin, reviews some of the adverse consequences of one class of therapies, inhaled corticosteroids (ICS). Although ICS therapy has improved the control of asthma markedly while diminishing the risk of corticosteroid adverse effects, a fear of potential adverse systemic effects continues to accompany their use. The safety profile of all ICS preparations, which focus on the antiinflammatory effects on the lung, is markedly better than oral glucocorticoids, but because these agents may be used for long periods of time in a large number of children, safety issues are paramount.
Dr David P. Skoner, from the Children’s Hospital of Pittsburgh, examines some of the challenges to balancing safety and efficacy associated with ICS therapy and explores the potential benefits of the leukotriene receptor antagonists as possible alternatives in the management of persistent mild pediatric asthma. In a separate article, he reviews some of the challenges and explores novel approaches to measuring outcomes and disease control in young children with asthma.