Written by Dr Jenny Tang
What is Bronchial Asthma ?
Bronchial Asthma is chronic inflammatory disease of the airways with increased sensitivity to triggers resulting in increased swelling of the airways, mucous production and tightening of the air passages with difficulty in breathing. Children with bronchial asthma often have other associated allergies e.g. food allergies, eczema and allergic rhinitis and these may occur at various times in childhood (Fig 1)
Asthma is a major cause of chronic morbidity and mortality throughout the world affecting an estimated 300 million individuals. The prevalence of asthma symptoms in children varies from 1 to more than 30 percent in different populations, and is still increasing in most countries, especially among children. It is the most common chronic disease in children affecting about 20% of school going children in Singapore. Also a significant number of these children report school absences due to asthma as well as exercise limitation and inability to participate in physical exercise.
Early Origins of Asthma and Natural History
Currently, the proposed development of allergic asthma is the result of gene environmental interactions with the inception of asthma in infancy and early childhood. The environmental factors include exposures to viral infections, microbial products, indoor and outdoor allergens, poor air quality and tobacco smoke.
A simple model of development of asthma can be divided into two stages. An induction phase and a maintenance phase. Early sensitisation to aeroallergens and exposure to high levels of perennial allergens have been shown to be associated with a chronic course of asthma with loss of lung function in later childhood and puberty vs. little impact of later sensitisation and exposure. Furthermore, the combination of viral infection and allergen sensitization enhances development of inflammation and altered airway function.
Wheezing is very common in childhood especially in preschoolers. Due to the complexity of initiating events it is often difficult to predict progression to asthma. Population studies have shown that about half of ‘early’ wheezers become asymptomatic by school age. These children have no personal or family history of allergies and demonstrate diminished lung function early in life that improves with age. Children who had wheezing that began in infancy persistent at age 6 demonstrated normal lung function initially, with reduced lung function by age 6 years and into adulthood. These children tend to be ‘allergic’ and have a family history of asthma. Children with late onset wheezing i.e. wheezing after age 3 years and still wheezing at age 6 tend to be ‘allergic’ and have normal lung function at birth and through teenage years. (Fig 2)
A good history and physical examination is often sufficient to confirm the diagnosis. (Table 1) Not all that wheezes is Asthma and it is pertinent to exclude other common causes of wheezing especially in younger children (Table 2).
Investigations may be helpful when diagnosis is in doubt, in severe or refractory cases or to aid in advising the likely long term outcomes. These include :
• Skin prick test to environmental allergens and food allergens.
• Blood eosinophil count.
• CXR and specialised imaging.
• Measurement of gastro-oesophageal reflux.
• Lung function tests including spirometry and impulse oscillometry (preschooler lung function)
• Exhaled nitric oxide and other assessments of airways inflammation
Assessment of severity (Table 3 ) and control (Table 4) with appropriate education on medication, devices and avoidance of triggers as well as optimal drug therapy is important to treatment success. The Asthma Control Test (ACT) is an easy way of assessing if a cild’s Asthma is well controlled. A score of more then 20 suggests uncontrolled asthma and a consult with paediatrician with experience in treatment of Asthma is recommended.
Medicines used for treatment of bronchial asthma fall into two groups; controller therapy and rescue therapy. Controller medications are used to treat the underlying inflammation in bronchial asthma and include steroidal e.g. fluticasone, budesonide and non steroidal medications e.g. montelukast. Rescue medications are used to reverse the acute symptoms of asthma which is due to airway narrowing and include salbutamol, terbutaline and ipratropium bromide. For most children with chronic asthma, medications are given via inhaled route i.e. Metered dose aerosol, dry powder inhaler or neubuliser. Use of a spacer with a metered dose inhaler in younger children allows optimal delivery of medications to the airways. Oral steroids or intravenous medications may be required with more severe attacks of asthma. The medications prescribed for each child may differ based on severity of asthma, age, patient preference and response to different medications.
Sublingual immunotherapy if used for treatment of associated allergic rhinitis may also improve asthma control and reduce medications used.
Environmental allergens play a significant role in the severity and control of asthma. House dust mites, animal dander, cockroaches and mould are some of the commoner allergens seen in our children. An integrated approach is usually necessary to bring down the level of environmental allergens.
Measures to prevent asthma may be aimed at the prevention of allergic sensitisation or the prevention of asthma in sensitised individuals. Other then the prevention of tobacco exposure both in utero and after birth, there is no widely accepted interventions that can prevent the development of asthma.
Exposure to tobacco smokes both prenatally and postnatal has been shown to impair lung development, increase the incidence of wheezing illnesses in childhood and the risk of allergic sensitisation in childhood.
There is currently insufficient information on the critical doses and timing of allergen exposure to permit intervention prenatally. The role of breast feeding has been extensively studied and exclusive breastfeeding in the early months have been shown to reduce asthma rates in childhood.
Bronchial asthma is the most common chronic disease in childhood and poses a burden to child family and society. Most children with asthma can have good control of disease with a normal quality of life. Early and accurate diagnosis, appropriate education, treatment, follow up and monitoring is critical successful management of the disease.
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