Asthma is a common condition that affects more than 10% of the population. Asthma is defined as reversible airway obstruction. It is caused by narrowing of the lower airways due to inflammation, and is therefore a disease of airway inflammation. Asthma patients might be normal most of the time, but when the disease exacerbates, the patient would cough, wheeze, and feel tight in the chest and short of breath. Asthmatic tendency is genetically determined, but the disease is triggered by external factors. Asthma most commonly starts during childhood, and the two most common causes are allergy and infection. Before the age of three, asthma is more commonly caused by virus infection, and the most common culprits are Respiratory Syncythial Virus (RSV), Rhinovirus and Adenovirus. Acute infections with these viruses can lead to croup, and patients develop high fever, cough, wheezing and dyspnea. In susceptible individuals, croup during the first two years of life can subsequently lead to recurrent wheezing illnesses. However, this problem often improves with age and goes into remission by about 8 years of age. Allergic asthma, on the other hand, often persists into adulthood. Even in those patients who seem to outgrow their asthma during their teens, recent studies have shown that many of them will develop asthma symptoms again in their 30s and 40s. The majority of patients with allergic asthma also suffer from allergic rhinitis, since both conditions are caused by allergen exposure. The most common allergens include house dust mites, cockroach, animal dander, mold spores and pollens.
The diagnosis of asthma is confirmed if the patient demonstrates lower airway obstruction on lung function testing that is reversible spontaneously or by administering an inhaled bronchodilator. However, some patients might have cough as their only symptom and do not demonstrate airway obstruction. In these cases, bronchial challenge test with inhaled methacholine or histamine will result in significant airway obstruction in those patients with airway hypersensitivity. This test is of great value in diagnosing patients with asthma masquerading as chronic cough. Some patients only develop asthma symptoms with exercise, and would thus require an exercise challenge. Once asthma is diagnosed, it is important to ascertain the cause of the disease, as the prognosis and treatment are quite different. In children, the absence of allergy is a good prognostic factor, since most of these patients will outgrow their asthma. In adults, one must consider other types of asthma such as occupational asthma and aspirin-sensitive asthma. Allergy testing is therefore an important part of asthma evaluation, since the treatment of allergic asthma includes allergen avoidance and desensitization. Patients with occupational asthma usually need to have a career change, but might be eligible for compensation.
House dust mite allergen is the major cause of allergic asthma worldwide, and even more so in Hong Kong where the climate is warm and humid. It is therefore important to minimize soft furnishings such as carpets, cushions and upholstered furniture at home. The bed is a major reservoir of mite allergen, and should be encased with dust-impermeable covers. It is often necessary to evict animals from home if the patient is allergic to them. The mainstay of drug treatment for asthma is inhaled corticosteroid. These drugs can prevent airway inflammation, and are effective in reducing symptoms, exacerbations and rescue medication use. They have been shown to prevent airway remodeling, a process that leads to irreversible loss of lung function. Patients with allergic asthma should seriously consider undergoing allergen desensitization treatment. Desensitization has been shown to reduce steroid requirement over time, and children with rhinitis who received desensitization are less likely to develop asthma.