Asthma is now considered a heterogeneous disease, meaning every asthmatic is different and cannot be treated the same. Because of this, researchers found it useful to break asthma into subgroups (also called subtypes or endotypes).
Subgroups are nice because they allow researchers to create guidelines tailored to each specific asthmatic. This makes it easier for physicians to help their asthmatic patients gain better control of their disease.
Here are some examples of subgroups:
1. Allergic Asthma. These patients develop adverse reactions to common allergens, such as dust mites, cockroach urine, pollen, mold, fungus, and animal dander. Treatment must focus on preventing and controlling both the asthma and allergy component, which can make it complicated to obtain optimal asthma control.
2. Exercise Induced Bronchospasm. Their air passages spasm and narrow after exercising, resulting in shortness of breath and coughing. Many respond well to a pre-treatment of albuterol prior to exercising. Others respond well to daily inhaled corticosteroid therapy.
3. Cross Country Skiing Induced Bronchospasm. Winter Olympians, especially those performing vigorous physical activity such as skiing, have an increased risk of developing asthma. A theory is that inhaling cold, dry air during vigorous exercise causes airway inflammation that causes airway remodelling, or a thickening of airway walls. These asthmatics are less likely to respond to corticosteroids.
4. Aspirin Exacerbated Respiratory Disease. This usually starts in adulthood after chronic exposure to nonsteroidal anti-inflammatory (NSAIDs) like aspirin. It’s associated with sinus infections, nasal polyps, and asthma attacks when exposed to NSAIDs. They generally respond well to leukotriene antagonists like Singulair.
5. Severe Asthma. They present with airway remodelling, or a thickening of the airway walls resulting in chronically obstructed airways. These asthmatics may present with asthma symptoms even on a good day, and generally have more frequent and severe asthma attacks that respond poorly to corticosteroids. These subgroup is often difficult to recognize and treat.
6. Obese Asthma. Some asthmatics may develop asthma as a result of poor eating habits. One theory suggests their immune systems might recognize saturated fat as an enemy, resulting in airway inflammation. Another theory suggests that hormones released from adipose (fat) tissue might cause a similar response. Daily treatment may include corticosteroids coupled with a diet and exercise program.
7. Late Onset Asthma. These patients usually do not have allergies. Their asthma is caused by chronic (everyday) exposure to something, such as gastrointestinal reflux, pollution, cigarette smoke, chemicals in the air at work, and woodstove smoke. They generally present with less lung function than allergic asthmatics. Some respond poorly to inhaled corticosteroids and better to oral corticosteroids. Making their asthma more difficult to control is they are more likely to present with other chronic conditions, such as COPD.
The Present. The above subgroups are based on clinical observations made by physicians, and there is no single test to help determine what subgroup an asthmatic belongs to. This, coupled with the fact that many asthmatics fall into more than one subgroup, may make some cases of asthma difficult to control.
The Future. However, researchers are now using molecules and genetics to fine tune these subgroups. This might ultimately lead to a single test to determine what subgroup one belongs to, and this should result in even better treatment options for individual asthmatics.
Another newer approach is using inflammatory cells found in asthmatic airways to create subgroups. Cells that are similar will determine how the disease will present, how severe it will be, who will have it, and what medicines will work.
Two examples are listed here:
1. Eosinophilic. They always present with some inflammation along the walls of their air passages, making their airways sensitive to asthma triggers. They respond well to corticosteroid therapy. This would probably represent most cases of asthma.
2. Neutrophilic. They have a thickening of airway walls that results in a certain degree of airway obstruction that is always present. They tend to have frequent and severe asthma episodes. This would probably include severe asthmatics.
Soon there might be a scientific breakthrough that results in a single test to determine what subgroup each asthmatic falls into. This should help researchers focus on better treatment options, resulting in ideal asthma control for all asthmatics.
References and Further Reading:
- Heterogeneity in Asthma, edited by Allan R. Brasier, pages 6-13
- The Evolution of Asthma: More Than Just A Lung Disease
- High Fat Diets May Cause Asthma In Children
- Exercise Induced Asthma Troubles Many – Even Olympians
- Asthma Phenotypes and Endotypes: An Evolving Paradigm for Classification.
A Registered Respiratory Therapist and asthmatic