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Asthma
Introduction
Asthma is a clinical syndrome that is characterized by recurrent or persistent symptoms of
shortness of breath, wheezing, cough and chest tightness which are usually reversible with
bronchodilator treatment or spontaneously. Narrowing of the airways is usually reversible.
Prevalence
It is about 1012% of adults and 15% of children affected by the disease worldwide.(Harrison
19
th
edition) The rising prevalence, which is associated with increased urbanization. Asthma can
present at any age, with a peak age of 3 years. In childhood, twice as many males as females
are asthmatic, but by adulthood the sex ratio has equalized.
Risk factors and triggers are basically of genetic and environmental factors.
1. Atopy
-is the major risk factor for asthma. Allergic rhinitis may be found in over 80% of asthmatic
patients, and atopic dermatitis (eczema). Environmental or genetic factor(s) predispose to the
development of asthma in atopic individuals. The most common allergens are derived from
house dust mites, cat and dog fur, cockroaches, grass and tree pollens, and rodents. Atopy is
due to the genetically determined production of specific IgE antibody, with many patients
showing a family history of allergic diseases.
2. Infections
Viral infections are common as triggers of asthma exacerbations.
3. Genetic Considerations
The familial association of asthma and a high degree of concordance for asthma in identical
twins indicate a genetic predisposition to the disease.
4. Diet
The role of dietary factors is controversial. However, diets low in antioxidants such as vitamin C
and vitamin A, magnesium, selenium are associated with an increased risk of asthma.
Vitamin D deficiency may also predispose to the development of asthma. Obesity is also an
independent risk factor for asthma, particularly in women, but the mechanisms are thus far
unknown. (Harrison 19
th
edition)
5. Air Pollution
Air pollutants such as sulfur dioxide, ozone, and diesel particulates, may trigger asthma
symptoms, but the role of different air pollutants in the etiology of the disease is much less
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certain. Indoor air pollution may be more important with exposure to nitrogen oxides from
cooking stoves and exposure to passive cigarette smoke.
6. Allergens
Inhaled allergens are common triggers of asthma symptoms. Exposure to house dust mites in
early childhood is a risk factor for allergic sensitization and asthma.
7. Occupational Exposure
Occupational asthma is relatively common and may affect up to 10% of young adults. (Harrison
20
th
edition) Occupational asthma may be suspected when symptoms improve during
weekends and holidays.
8. Other Factors Lower maternal age, duration of breast-feeding, prematurity and low
birthweight, and inactivity have been implicated as possible etiology of asthma.
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Pathophysiology
Asthma is associated with a specific chronic inflammation of the mucosa of the lower airways.
One of the main aims of treatment is to reduce this inflammation.
Pathology
The airway mucosa is infiltrated with activated eosinophils and T lymphocytes, and there is
activation of mucosal mast cells. The degree of inflammation is poorly related to disease
severity and may be found in atopic patients without asthma symptoms. Direct observation by
bronchoscopy indicates that the airways may be narrowed, erythematous, and edematous.
These pathologic changes do not extend to the lung parenchyma; peripheral airway
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