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Bronchial Asthma : Causes, Symptoms, Diagnosis & Treatment

Bronchial Asthma : Causes, Pathogenesis, Symptoms, Diagnosis & Treatment

Definition

  • Asthma is a chronic inflammatory disorder of the airways defined as increased responsiveness of the tracheobronchial tree to a variety of stimuli resulting in widespread spasmodic narrowing of the air passages which may be relieved spontaneously or by therapy.
  • The hallmarks of the disease are intermittent and reversible airway obstruction, chronic bronchial inflammation with eosinophils, bronchial smooth muscle cell hypertrophy and hyperreactivity, and increased mucus secretion.
  • Many cells play a role in the inflammatory response, in particular eosinophils, mast cells, macrophages, lymphocytes, neutrophils, and epithelial cells.

Symptoms

  • Asthma is characterised by recurrent episodes or paroxysms of wheezing, breathlessness, dyspnoea ,chest tightness, and cough, particularly at night and/or early in the morning.
  • Most attacks typically lasts for a few minutes to hours.
  • When a severe paroxysm occurs that does not respond to therapy and persists for days and even weeks, condition is termed as status asthmaticus.

Types

Based on stimuli initiating bronchial asthma :
1. Atopic/Extrinsic/Allergic Asthma 

  • This is the most common type of asthma, usually beginning in childhood, and is a classic example of type I IgE–mediated hypersensitivity reaction.
  •  A positive family history of atopy and/or asthma is common, and asthmatic attacks are often preceded by allergic rhinitis, urticaria, or eczema.
  • The disease is triggered by environmental antigens, such as dusts, pollen, animal dander, and foods or sometimes by Infections .

2. Non-Atopic/Intrinsic/Idiosyncratic Asthma

  • This type of asthma develops later in adult life.
  • Patients with non-atopic forms of asthma do not have evidence of allergen sensitization.
  • Skin test results usually are negative.
  • A positive family history of asthma is less common.
  • It is commonly triggered by Respiratory infections due to viruses (e.g., rhinovirus, parainfluenza virus) and inhaled air pollutants (e.g., sulfur dioxide, ozone, nitrogen dioxide).
  • It is thought that virus-induced inflammation of the respiratory mucosa lowers the threshold of the subepithelial vagal receptors to irritants.

Although the connections are not well understood, the ultimate humoral and cellular mediators of airway obstruction (e.g., eosinophils) are common to both atopic and nonatopic variants of bronchial asthma, so they are treated in a similar way.
Based on agents/events causing bronchial asthma :
1. Drug induced Asthma

  • Several pharmacologic agents provoke asthma, aspirin being the most striking example.
  • Patients with aspirin sensitivity present with recurrent rhinitis and nasal polyps, urticaria, and bronchospasm.

2. 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. Asthma attacks usually develop after repeated exposure to the inciting antigen(s).
    Pathogenesis
  • The major etiologic factors of asthma are genetic predisposition to type I hypersensitivity (atopy), acute and chronic airway inflammation, and bronchial hyperresponsiveness to a variety of stimuli.
  • The inflammation involves many cell types and numerous inflammatory mediators, but the role of type 2 helper T (TH2) cells may be critical to the pathogenesis of asthma.
  • The classic atopic form of asthma is associated with an excessive TH2 reaction against environmental antigens.
  • Cytokines produced by TH2 cells account for most of the features of asthma—IL-4 stimulates IgE production, IL-5 activates eosinophils, and IL-13 stimulates mucus production and also promotes IgE production by B cells.
  • Asthma is a complex genetic disorder in which multiple susceptibility genes interact with environmental factors to initiate the pathologic reaction.
  • There is significant variation in the expression of these genes and in the combinations of polymorphisms that effect the immune response or tissue remodeling.

Treatment

Bronchial Asthma may be relieved spontaneously or by therapy (drugs) as following :

  • Bronchodilators
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  • Corticosteroids
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  • Leukotriene antagonists
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  • Mast cell stabilizers
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  • Anti-lgE antibody
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