Previously the condition was divided into two defined types of asthma: extrinsic (allergic) and intrinsic (nonallergic) asthma. Now-a-days, the illness can be classified into a number of different types as following:
Extrinsic or allergic asthma (AA) is the more common type and represents about 90% of all cases of asthma. Allergic asthma typically develops in childhood and often, there is a family history of allergies. Allergen exposure is a significant trigger of exacerbations for many patients with this type of asthma.
Causes of Allergic Asthma
The causes of AA are wide ranging. The most frequent causative allergens are dust mites, pollens, molds, pet dander and even cockroach droppings. It is best to avoid the exposure to known allergens in order to prevent recurrence of the symptoms.
Other allergens include irritants in the air including smoke from cigarettes, wood fires and strong fumes like household sprays, paint, gasoline, perfumes and scented soaps. Although many are not actually allergic to these particles, they can aggravate the inflamed and sensitive airways. Smoking is a common trigger of asthma symptoms for all ages. Studies have shown a clear link between secondhand smoke and asthma, especially in young people.
Childhood Allergic Asthma
Most childhood asthma is considered an allergic type of asthma. Young children are a particularly vulnerable for environmentally mediated asthma and the economic burden associated with this disease is substantial.
According to a recent literature review, childhood allergic rhinitis was associated with a 2–7-fold increased risk of asthma in preadolescence, adolescence or adult life.1 Both prenatal and postnatal passive smoking have been linked with respiratory symptoms and asthma in childhood. In utero exposure to heavy smoking was found to have a stronger effect than postnatal environmental tobacco exposure in the development of asthma in adolescence.2
Intrinsic asthma (IA) represents about 10% of all cases. It usually develops after the age of 30 years and is not typically associated with allergies. Women are more frequently involved and many cases seem to develop after a respiratory tract infection. Triggers of IA include perfume, smoke, cold air, cleaning fumes and gastroesophageal reflux disease. Intrinsic asthma tends to be less responsive to treatment than AA.
Exercise-induced asthma (EIA) is a condition in which vigorous physicalactivity triggers acute airway narrowing in people with heightenedairway reactivity. Many of these people have allergies or a family history of allergies.
This asthma can affect anyone at any age. Although can be seen in any sport, it is more common in predominantly aerobic activities. This is due to the fact that the lungs lose their moisture and heat during strenuous activities. Coughing is the most common symptom in EIA although there may be more severe symptoms, particularly in cold and dry conditions. Prophylactic medications such as asthma inhalers or bronchodilators used prior to exercise can control and prevent EIA symptoms.
Occupational asthma (OA) is now the most common work-related respiratory disorder in the industrialized nations. About 9–15% of adult-onset asthma is considered attributable to occupational exposures.3 Occupational asthma is attributable to a particular environment such as that associated to the exposure of high concentrations of irritant gases, fumes, chemicals or dust. There are two types of OA based on the onset of symptoms which is either immediately after an exposure (non-latent) or that which occurs after a prolonged period of exposure (latent).
The primary goal in managing OA is to avoid further exposure to the offending agent. Pharmacological management of OA is the same as that for nonoccupational asthma including judicious use of systemic and inhaled steroids and bronchodilator medications.
Nocturnal or sleep-related asthma affects people when they are sleeping. Although not a specific form of asthma, nocturnal worsening of symptoms is a very common component of asthma. Indeed, patients with poorly controlled asthma often awaken between 2:00 and 4:00 a.m. with symptoms of the illness.
The precise cause of nocturnal asthma is not known. Possible mechanisms include sleep-related changes in airway tone, lung volumes and airway inflammation, prolonged exposure to allergens in the bedroom, a decrease in room temperature, late asthmatic reactions to daytime stimuli, gastroesophageal reflux related to supine posture and an increase in the intervals between intakes of asthma medications.
Steroid resistant asthma (SRA) refers to a group of asthmatics who have persistent airway obstruction and immune activation despite treatment with high doses of systemic glucocorticoids (corticosteroids).
The SRA patients are the most difficult and challenging to manage. They usually display severe symptoms and are resistant to the most effective class of medications used to treat this disorder. Successful management of the SRA patient often includes frequent clinical visits and serial objective measures of lung function. The management plan often requires optimal use of bronchodilator drugs along with the use of alternative antiinflammatory and/or immunomodulator drugs.
- Burgess JA, Walters EH, Byrnes GB, Matheson MC, Jenkins MA, Wharton CL, et al. Childhood allergic rhinitis predicts asthma incidence and persistence to middle age: A longitudinal study. J Aller Clin Immunol. 2007; 120(4): 863–869.
- Alati R, Al Mamun A, O’Callaghan M, Najman JM, Williams GM. In utero and postnatal maternal smoking and asthma in adolescence. Epidemiology. 2006; 17(2): 138–144.
- Mapp CE, Boschetto P, Maestrelli P, Fabbri LM. Occupational asthma. Am J Respir Crit Care Med. 2005; 172: 280–305.