Allergic disorders are among the most common problems seen by pediatricians and primary care physicians, affecting over 25% of the population in developed countries. In the most recent National Health and Nutrition Examination Survey, 46% of the population had positive test responses to one or more allergens. In children, the increased prevalence of asthma, allergic rhinitis, and atopic dermatitis has been accompanied by significant morbidity and school absenteeism, with adverse consequences for school performance and quality of life, as well as economic burden measured in billions of dollars. In this chapter, atopy refers to a genetically determined predisposition to develop IgE antibodies found in patients with asthma, allergic rhinitis, and atopic dermatitis.
Essentials of Diagnosis & Typical Features
- Episodic symptoms of airflow obstruction including wheezing, cough, and chest tightness.
- Airflow obstruction at least partially reversible.
- Exclusion of alternative diagnoses.
Asthma is the most common chronic disease of childhood, affecting over 7.1 million children in the United States. While current prevalence rates for asthma have increased in the past decade, the rate of asthma attack in the past year has been stable. One of 10 children has current asthma, and nearly two out of every three children affected have had at least one attack due to asthma in the past year. There is still a disproportionately higher health care utilization for asthma among children compared to adults affected by this disease. The burden of hospitalizations and emergency department or ambulatory and office visits, all indicators of severe asthma and risk factors for fatal asthma, impose significant costs to the health care system and to families, caretakers, schools, and parents’ employers. Indirect costs primarily from loss of productivity due to school/work absences are harder to measure, yet considerable. Asthma remains a potentially life-threatening disease for children; the rate of asthma deaths was 0.3 per 10,000 children with current asthma. The prevalence and morbidity and mortality rates for asthma are higher among minority and inner city populations. The reasons for this are unclear but may be related to a combination of more severe disease, poor access to health care, lack of asthma education, delay in use of appropriate controller therapy, and environmental factors (eg, irritants including smoke and air pollutants, and perennial allergen exposure).
Up to 80% of children with asthma develop symptoms before their fifth birthday. Atopy (personal or familial) is the strongest identifiable predisposing factor. Sensitization to inhalant allergens increases over time and is found in the majority of children with asthma. The principal allergens associated with asthma are perennial aeroallergens such as dust mite, animal dander, cockroach, and Alternaria (a soil mold). Rarely, foods may provoke isolated asthma symptoms.
About 40% of infants and young children who have wheezing with viral infections in the first few years of life will have continuing asthma through childhood. Viral infections (eg, respiratory syncytial virus [RSV], rhinovirus, parainfluenza and influenza viruses, metapneumovirus) are associated with wheezing episodes in young children. RSV may be the predominant pathogen of wheezing infants in the emergency room setting, but rhinovirus can be detected in the majority of older wheezing children. Furthermore, RSV and parainfluenza have been associated with more severe respiratory illnesses, but in general, rhinovirus is the most commonly identified respiratory virus with wheezing episodes. It is uncertain if these viruses contribute to the development of chronic asthma, independent of atopy. Severe RSV bronchiolitis in infancy has been linked to asthma and allergy in later in childhood. Although speculative, individuals with lower airways vulnerability to common respiratory viral pathogens may be at risk for persistent asthma.
Exposure to tobacco smoke, especially from the mother, is also a risk factor for asthma. Other triggers include exercise, cold air, cigarette smoke, pollutants, strong chemical odors, and rapid changes in barometric pressure. Aspirin sensitivity is uncommon in children. Recent evidence suggests that acetaminophen exposure increases the risk of wheezing and asthma. Psychological factors may precipitate asthma exacerbations and place the patient at high risk from the disease.
Pathologic features of asthma include shedding of airway epithelium, edema, mucus plug formation, mast cell activation, and collagen deposition beneath the basement membrane. The inflammatory cell infiltrate includes eosinophils, lymphocytes, and neutrophils, especially in fatal asthma exacerbations. Airway inflammation contributes to airway hyperresponsiveness, airflow limitation, and disease chronicity. Persistent airway inflammation can lead to airway wall remodeling and irreversible changes.
The diagnosis of asthma in children is based largely on clinical judgment and an assessment of symptoms, activity limitation, and quality of life. For example, if a child with asthma refrains from participating in physical activities so as not to trigger asthma symptoms, their asthma would be inadequately controlled but not detected by the standard questions. In the National Asthma Education and Prevention Program (NAEPP) clinical guidelines, asthma control is introduced as an approach to assess the adequacy of current treatment, and to improve care and outcomes for children with asthma. For children with asthma, numerous validated instruments and questionnaires for assessing health-related quality of life and asthma control have been developed. The Asthma Control Test (ACT, www.asthmacontrol.com), the Asthma Control Questionnaire (ACQ, www.qoltech.co.uk/Asthma1.htm), and the Asthma Therapy Assessment Questionnaire (ATAQ, www.ataqinstrument.com) for children 12 years of age and older, and the Childhood ACT for children 4–11 years of age are examples of self-administered questionnaires that have been developed with the objective of addressing multiple domains of asthma control such as frequency of daytime and nocturnal symptoms, use of reliever medications, functional status, missed school or work, and so on. A five-item caregiver-administered instrument, the Test for Respiratory and Asthma Control in Kids (TRACK), has been validated as a tool to assess both impairment and risk presented in the NAEPP EPR3 guidelines in young children with recurrent wheezing or respiratory symptoms consistent with asthma.