Asthma is a chronic respiratory disease that affects millions of people worldwide. It causes difficulty in breathing due to inflammation and narrowing of the airways. It affects people of all ages, with an estimated 339 million individuals affected worldwide. While the exact cause of asthma is not fully known, a combination of genetic and environmental factors plays a role.
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What is Asthma:
Asthma is a complex respiratory disease that has been shown to exhibit significant heterogeneity in terms of clinical features, underlying pathophysiological mechanisms, and response to treatment. As a result, the traditional classification of asthma based solely on clinical symptoms is being replaced by a more refined approach that considers the underlying biological mechanisms involved.
There are two important words to know: “phenotypes” and “endotypes”. Phenotypes refer to observable characteristics, including clinical presentation, triggers, and response to treatment. Endotypes, on the other hand, refer to the underlying pathophysiological mechanisms that drive the disease.
Several types of asthma with different phenotypes and endotypes have been identified, so far.
Regarding endotypes, the most well-known is type 2 (T2) inflammation, which is driven by the activation of immune cells such as Th2 cells, mast cells, and eosinophils This type of asthma is usually associated with allergic asthma and some cases of non-allergic asthma. Other endotypes include type 1 (T1) inflammation, associated with neutrophilic airway inflammation, and mixed granulocytic inflammation, characterized by the presence of both eosinophils and neutrophils in the airways.
Identifying asthma phenotypes and endotypes is essential in guiding appropriate treatment and management strategies. For example, if you have allergic asthma, staying away from things you’re allergic to and getting special medicines called immunotherapy can help you feel better. Targeted therapies, such as biologics, have been developed for specific endotypes of severe asthma, such as anti-IL-5 therapy for eosinophilic asthma.
What are some common asthma phenotypes?
There are several phenotypes of asthma, which refer to different subtypes of the disease with distinct clinical and pathophysiological features. The most common phenotypes include allergic, non-allergic, exercise-induced, and occupational asthma. Understanding the differences between these types can help in better management and treatment of the disease.
Allergic Asthma, The Most Common Type:
Allergic asthma is the most prevalent asthma phenotype and is triggered by exposure to allergens such as dust mites, pollen, and pet dander. It is characterized by specific immunoglobulin E (IgE) antibodies to these allergens and the activation of inflammatory cells in the airways, such as eosinophils and mast cells.
Non-Allergic Asthma:
Non-allergic asthma, on the other hand, is not associated with the presence of IgE antibodies to allergens. Instead, it is triggered by respiratory infections, air pollution, cold air, exercise, and stress. Non-allergic asthma is characterized by activating inflammatory cells in the airways, such as neutrophils and T-lymphocytes.
Exercise-Induced Asthma:
Exercise-induced asthma is a subtype of asthma that is triggered by physical activity. The narrowing of the airways characterizes it due to the release of inflammatory mediators, such as histamine and leukotrienes, during exercise. The symptoms of exercise-induced asthma typically occur 5-10 minutes after starting exercise and may include coughing, wheezing, chest tightness, and shortness of breath.
Occupational Asthma:
Occupational asthma is a subtype of asthma that is caused by exposure to irritants in the workplace (such as chemicals, dust, or fumes). It is characterized by the activation of inflammatory cells in the airways due to exposure to chemicals, dust, and fumes. The symptoms of occupational asthma may include coughing, wheezing, chest tightness, and shortness of breath, and may worsen during the workweek and improve on weekends or vacations.
Recognizing Different Types of Asthma:
Diagnosing the specific type of asthma involves a thorough evaluation of medical history, symptoms, and physical examination. Several diagnostic tests can help in identifying the underlying phenotype:
1. Allergic Asthma:
Skin prick tests or measuring allergen-specific IgE levels can identify allergen triggers.
2. Non-Allergic Asthma:
Tests like sputum induction can help diagnose this type by analyzing the presence of inflammatory cells.
3. Exercise-Induced Asthma:
Exercise challenge testing monitors lung function before and after exercise to diagnose this type.
4. Occupational Asthma:
Identifying the specific substance causing asthma is done through an occupational history and sometimes inhalation challenge testing.
By understanding the different types of asthma, healthcare providers can develop personalized treatment plans that target the underlying mechanisms of the disease. Treatment strategies may include allergen avoidance, immunotherapy, and targeted therapies like biologics.
Breathing exercises may provide some relief from allergy symptoms, but they don’t directly affect the allergy itself. They are useful for managing allergy-related symptoms such as nasal congestion, sneezing, itching, and shortness of breath.
Deep, mindful breathing can help reduce the stress and anxiety associated with allergic reactions, improving overall well-being and proper breathing can help keep the airways open, facilitating airflow and reducing the feeling of chest tightness.
Conclusion:
Asthma is a complex respiratory disease with various types, each requiring specific management approaches. Recognizing the different types and understanding their triggers can help individuals with asthma and their healthcare providers in effectively managing the condition. By optimizing treatment based on the specific asthma phenotype, patients can lead healthier lives with improved respiratory function and reduced symptoms.
Bibliography:
Global Initiative for Asthma (GINA). Global Strategy for Asthma Management and Prevention. Available at https://ginasthma.org/wp-content/uploads/2021/04/GINA-Main-Report-2021-V2-WMS.pdf
Chung KF, Wenzel SE, Brozek JL, et al. International ERS/ATS guidelines on definition, evaluation and treatment of severe asthma. Eur Respir J. 2014;43(2):343-373. doi:10.1183/09031936.00202013
Bateman ED, Hurd SS, Barnes PJ, et al. Global strategy for asthma management and prevention: GINA executive summary. Eur Respir J. 2008;31(1):143-178. doi:10.1183/09031936.00138707
American Thoracic Society (ATS). Diagnosis and management of asthma. Available at https://www.thoracic.org/patients/patient-resources/resources/asthma-diagnosis-and-management.pdf
