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Allergic asthma is a chronic inflammatory disease of the respiratory system with complicated pathophysiology, variable clinical expression, and a variety of treatment options. It is triggered by allergens, but predisposition also plays an important role.

Allergic asthma is the most common form of bronchial asthma and it is identified in more than 60 percent asthma patients, according to Asthma and Allergy Foundation of America (AAFA). Furthermore, some other types which are not classified as allergic asthma also have an allergic origin. This is the case with Adult Onset Asthma, which is triggered by hypersensitivity to allergens in about 30 percent of cases. From this we can say that allergies are by far the most common cause of asthma in all age groups.

What happens in allergic asthma?

First of all, we know that some people are more prone to allergies than others. Therefore, we need to underline the imbalance in the immune system functioning as the first step in developing an allergy. This imbalance can appear due to a genetic predisposition or environmental factors, such as overexposure to some allergens. The exact mechanism of how any of these factors manage to cause the malfunctioning of the immune system is unknown. What we know is that that there is imbalance between the activity of the two subsets of CD4+ T-lymphocytes – Th1 and Th2.

It is hard to explain their complex roles in short, but here is a brief overview:

  • Th1 lymphocytes are responsible for defending us from intracellular microbes (mostly viruses) and for some autoimmune disorders.
  •  Th2 lymphocytes are the main factor in allergies, because they produce substances (interleukins) which stimulate the production of IgE antibodies - the antibodies which are the main mediators in allergic reactions.

The imbalance of these two subtypes of lymphocytes in favor of Th2 has been found in persons with an atopic constitution – a tendency to develop multiple allergies.

Scientists are trying to use different approaches in order to establish the optimal balance between Th1 and Th2 immune response, hoping that it will solve problems with allergies, which are becoming more and more common in the modern world.

What are the most common triggers of allergic asthma?

Allergens are substances that initiate an immune response in some people, even though it is unnecessary. That leads to allergic reactions, from mild (urticaria) to severe (angioedema and anaphylactic shock). If allergens happen to be present in the air, they can produce an immune response in the respiratory tract. Prolonged exposure to some inhalatory allergens can cause the onset of allergic bronchial asthma, which is a chronic inflammatory disease of the respiratory system causing reversible airway obstruction.

Although you can really be allergic to anything, some of the most common inhalatory allergens which cause allergic asthma include:

  • Tree and grass pollen
  • Dust mites
  • Pet hair

Among them, some allergens have been shown more potent in causing asthma than others. For example, birch pollen is a very potent allergen and it often causes asthma in both children and adults.

What are the symptoms of allergic asthma?

Asthma has similar symptoms regardless of the origin. It can be summarized as a chronic, self-sustaining inflammatory disease of the respiratory tract which includes reversible airway obstructions and increased mucus production.

Upon contact with an allergen, people with allergic asthma develop symptoms, which can be mild, moderate, or severe. They include:

  • Breathing difficulties (especially exhalation problems)
  • Cough
  • Wheezing
  • A feeling of tightness, or sometimes pain in the chest
You have probably noticed the word "reversible" several times in this article, so it is time to explain it. Namely, people with uncomplicated allergic asthma only experience symptoms in the presence of allergens. In the absence of allergens, their respiratory function returns to normal.

Diagnosis of allergic asthma

The diagnosis of asthma is performed based on patient’s reported symptoms, physical examination, spirometry, an allergy skin prick test, and laboratory tests.

  • Spirometry is a test designed to measure respiratory function by measuring respiratory volumes and capacities. In persons with asthma, a particularly important volume is called FEV1 – the air volume exhaled in the first second of forced expiration after maximum inhalation. Persons with asthma have lower FEV1 in presence of allergen (for example during tree pollen season). After that, a bronchodilator test is usually performed in order to confirm that the airway obstruction is reversible. About 15 minutes after inhalation of a bronchodilator, FEV1 should increase and become close to normal.
  • A skin prick test usually shows hypersensitivity to some inhalatory allergens.
  • Laboratory tests can sometimes reveal a higher percentage of eosinophils (types of leucocytes which release histamine in allergic reactions), some leukotriens, and IgE antibodies.

Allergic asthma treatment

Identifying the allergen, and reducing exposure to it is the first step in the treatment of allergic asthma symptoms. Since this is a chronic and self-sustaining disorder, the pathological process will still exist, but the symptoms will be very mild if the allergen is eliminated. Of course, that is rarely possible, and different medications and even combinations of them are prescribed to patients with allergic asthma:

  • Antihistamines are very efficient in eliminating the symptoms of allergy and they often help people with seasonal allergies.
  • Inhalatory corticosteroids are the main drugs which actually reduce the intensity of inflammation in the respiratory tract and lower the frequency of asthma attacks.
  • Inhalatory bronchodilators reduce the airway obstruction. Beta-agonists (salbutamol) and anticholinergics (ipratropium bromide) are the main drugs used for this purpose.
  • Leukotriene inhibitors block the activity of leukotriens – the chemicals produced by the immune system which are some of the main mediators in the inflammatory response in asthma patients.

In the treatment of acute attacks, inhalatory bronchodilators are the first line drugs, but if they do not eliminate the symptoms, then doctors can use other, more aggressive drugs, such as aminophylline and intravenous corticosteroids.

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