Asthma is a chronic relapsing inflammatory disorder characterized by hyperreactive airways, leading to episodic, reversible bronchoconstriction , owing to increased responsiveness of the tracheobronchial tree to various stimuli. Some of these stimuli would have little or no effect on nonasthmatics with normal airways. Most asthma is associated with atopy, which represents increased susceptibility to generate immunoglobulin E (IgE) in response to external allergens
Those afflicted experience unpredictable disabling attacks of severe dyspnea, coughing, and wheezing triggered by sudden episodes of bronchospasm. Between the attacks patients may be virtually asymptomatic, but in some persons chronic bronchitis or cor pulmonale supervenes. Rarely a state of unremitting attacks (status asthmaticus) proves fatal; usually such patients have had a long history of asthma. In some cases , the attacks are triggered by exposure to an allergen to which the patient has previously been sensitized, but no allergic trgger can be identified. There has been a significant increase in the incidence of asthma in the western world in the past three decades.
Asthma has traditionally been divided into two basic types extrinsic and intrinsic. Extrinsic asthma is initiated by a type 1 hyperssensitivity reaction induced by exposure to an extrinsic antigen. Subtypes include atopic asthma occupational asthma, and allergic bronchopulmonary aspergillosis. The last-mentioned describes colonization of asthmatic airways with Aspergillus organisms , followed by development of additional IgE antibodies. In contrast, intrinsic asthma is initiated by divese, nonimmune mechanisms, include ingestion of aspirin; pulmonary infections, especially viral; cold ; inhaled irritants;stress and exercise. As with other classification schemes patients often ignore categories and manifest overlapping characteristics. For example , the patient with extrinsic asthma dn increased airway hyperreactivity is also more likely to manifest bronchospasm after exposure to one of the agents associated with intrinsic asthma.
Pathogenesis.
The two major components of asthma are chronic airway inflammation and bronchial hyperresponsiveness. The inflammation involves manyh cell types and numerous inflammatory mediators, but the precise relationship of specific inflammatory cells and the mediators to airway hyperreactivity is not fully understood.
Atopic Asthma.
This most common type of asthma usually begins in childhood. The disease is triggered by environmental antigens, such as dusts, pollens, animal dander, and foods, but potentially any antigen is implicated. A positive family history of atopy is common, and asthmatic attacks are often proceeded by allergic rhinitis, urticaria, or echzema.
Nonatopic Asthma.
The second large group is the nonatopic, or nonreaginic, variety of asthma, which is the most frequently triggered by respiratory tract infection. Viruses rather than bacteria are the most common provokers. A positive family history is un common. Serum IgE levels are normal and there are no other associated allergies.
Drug- Induced Asthma.
Several pharmacologic agents provoke asthma. Aspirin-sensitive asthma is an uncommon rhinitis and nasal polyphs. These individuals are exqisitely sensitive to small doeses of aspirin, and they experience not only asthmatic attacks, but also urticaria.
Occupational Asthma
This form of asthma is stimulated by fumes (epoxy resins, plastics), organic and chemical dusts (wood, cotton,platinum), gases (toluene), and other chemicals ( formaldehyde, penicillin products).
By: sanjoea