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Asthma

What is asthma?

Asthma is a common respiratory condition that involves chronic airway inflammation, hyperresponsiveness, remodeling and narrowing.1,2 It is characterized by variable respiratory symptoms and variable expiratory airflow limitation, which can later become persistent.1 It is a major noncommunicable disease with high morbidity and can lead to mortality in severe cases.3 Although there is currently no cure for asthma, effective management and treatment of symptoms can improve quality of life.4

The pathophysiology of asthma

Asthma is a heterogenous disease with various underlying disease processes.1 Whilst no strong correlation has been observed between specific disease processes and clinical features or treatment responses, asthma has 'phenotypes' or identifiable clusters of demographic, clinical and pathophysiological characteristics.1 Some of the most common phenotypes include:1

  • Allergic asthma
  • Non-allergic asthma
  • Adult-onset, or late-onset, asthma
  • Asthma with persistent airflow limitation
  • Asthma with obesity

The key pathophysiological changes in asthma include:5-8

  • Bronchoconstriction – the bronchial smooth muscle contracts and the airways narrow.5
  • Airway inflammation - is a multicellular process involving Th2 lymphocytes, mast cells, neutrophils, macrophages, cytokines and eosinophils, and chronic inflammation may lead to airway remodeling.6-8
  • Airway hyperresponsiveness – an exaggerated bronchoconstrictor response that can be triggered by a variety of stimuli, such as allergens or irritants. The intensity of the response is regulated by underlying airway inflammation, as well as structural changes and dysfunctional neuroregulation.5
  • Airway remodeling – structural changes to airway walls, which may include thickening of the epithelium, fibrosis, mucous hypersecretion and mucous gland hyperplasia, smooth muscle hypertrophy and blood vessel proliferation and dilation. These changes may be permanent and increase airflow obstruction and airway responsiveness.5

Facts about asthma9

incidence

Asthma prevalence

The asthma prevalence of Taiwan was 7.57%-11.53% in 2000-2011, became one of the highest adult asthma prevalence rates in Asia.

asthama-peoples

Increased dramatically in young people

The annual prevalence rate was 2.84%-11.85% in 2000 to 2011 in the group aged 18–30 years.

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Higher prevalence in elderly people

Higher annual prevalence rate in the group aged ≥ 60 years. The burden of asthma is greater on elderly people in mortality, hospitalization, and medical costs.

Symptoms

Patients with asthma typically present with patterns of respiratory symptoms that are characteristic of asthma, as well as variable expiratory airflow limitation.1 Symptoms vary between individuals and can lead to impaired quality of life, with some patients suffering from episodic exacerbations or asthma attacks.8

Symptoms and airflow limitation characteristically vary over time and in intensity, but they also may resolve spontaneously or in response to medication.1

Asthma should be considered in patients with the following symptoms:1

  1. Wheeze
  2. Dyspnoea (shortness of breath)
  3. Chest tightness
  4. Cough

The causes of asthma are not well understood, but it is thought to arise as consequence of complex gene-environment interactions, which can trigger allergic reactions or irritate the airways.12-14

Genetic predisposition

  • Asthma clusters in families12
  • Atopy5

Environmental exposures

  • Indoor allergens, e.g. pollution or house dust mites10
  • Outdoor allergens, such as pollens and moulds10
  • Tobacco smoke10
  • Chemical irritants in the workplace10
  • Air pollution10

Occupational exposures

Occupational exposure to allergens or irritants can cause occupational asthma in adults11

Other triggers:

  • Cold air10
  • Exercise1
  • Viral infections1
  • Certain medications, e.g. aspirin, non-steroidal anti-inflammatory drugs and beta-blockers1,10

The crude annual prevalence of diagnosed asthma increased from 7.57% of the adult population in 2000 to 11.53% in 2011. Higher annual asthma prevalence rates were observed in patients who were aged 60 years, female, had a low insurance premium salary level, or resided in a rural area or aging society. The annual prevalence rate increased dramatically in the group aged 18–30 years, from 2.84% in 2000 to 11.85% in 2011.9

The prevalence of adult asthma in Taiwan is relatively high. In the similar periods, our estimated prevalence rate was similar to those in Scotland (8.5%), the United States (7.21%-8.52%), and the United Arab Emirates (8%-12%); higher than those in Bangladesh (3.9%), China (0.8%-1.0%), Finland (3.5%), Hong Kong (5.8%), India (1.9%-2.9%), Iran (1.4%-6.1%), Japan (3.4%-4.2%), South Korea (2.4%-5.8%), Singapore (5.1%), and Thailand (2.9%); and lower than that in South Australia (12.2%-13.4%).9

A significant increasing trend was observed in the prevalence of adult asthma in Taiwan, which has also been reported in South Australia, Finland, Hong Kong, Japan, South Korea, Scotland, and the United States. As shown, Taiwan has one of the highest adult asthma prevalence rates in Asia.9

The crude annual incidence fluctuated between 0.29% and 0.56% from 2000 to 2011. Higher annual asthma incidence rates were observed in patients who were aged 60 years, female, or resided in areas with low urbanization levels, such as an aging society and rural and undeveloped areas. Taiwan has a relatively low asthma incidence rate. The burden of asthma is greater on elderly people in mortality, hospitalization, and medical costs.9

Difficult-to-treat and severe asthma

Some people will have difficult-to-treat asthma, where they struggle to control their symptoms and may experience frequent attacks despite receiving pharmacological treatment.13-15 Difficult-to-treat asthma can have several causes, including smoking, comorbidities, poor inhaler technique and poor therapy adherence, and can be managed with support and the correct treatment.13-15

A much smaller subset of people will have severe asthma where despite having good treatment adherence and inhaler technique their asthma remains uncontrolled.13-15 These patients may experience symptoms that impact their daily life, as well as serious attacks for which they are hospitalised.15 However, certain add-on therapies can help to improve their symptoms.15

In the UK, approximately 17% of people with asthma are thought to have difficult-to-treat asthma, whilst only 4% are estimated to have severe asthma.13

References:

  1. Global Strategy for Asthma Management and Prevention. Global Initiative for Asthma (GINA) 2020.

  2.  Kudo M et al. Front Microbiol 2013;4:263.

  3. Dharmage S et al. Front Pediatr 2019;7:246.

  4. World Health Organization. Asthma factsheet. https://www.who.int/news-room/fact-sheets/detail/asthma. Accessed 03 May 2021.

  5. National Asthma Education and Prevention Program, Third Expert Panel on the Diagnosis and Management of Asthma. Expert Panel Report 3: Guidelines for the Diagnosis
    and Management of Asthma. Bethesda (MD): National Heart, Lung, and Blood Institute (US); 2007 Aug.

  6. Athari SS. Signal Transduct Target Ther 2019;4:45.

  7. Holgate ST. Clinical and Experimental Allergy, 38 : 872–897.

  8. Holgate ST, Thomas, M. Asthma. Middleton’s Allergy Essentials. 2017;151–204.

  9. Ma YC, et al. PLoS One 2015;10(10):e0140318.

  10. World Health Organization. Causes of Asthma. https://www.who.int/respiratory/asthma/causes/en/. Accessed 03 May 2021.

  11. Papi A et al. Lancet 2018;391(10122):783−800.

  12. NICE guideline [NG80]. Asthma: diagnosis, monitoring and chronic asthma management, 2017. www.nice.org.uk/guidance/ng80. Accessed 03 May 2021.

  13. Asthma UK. Difficult to control asthma. https://www.asthma.org.uk/advice/understanding-asthma/types/difficult-control-asthma/. Accessed 03 May 2021.

  14. Currie GP et al. BMJ 2009;338:b494.

  15. Global Strategy for Asthma Management and Prevention. Global Initiative for Asthma (GINA) Difficult-to-Treat and Severe Asthma in Adolescent and Adult Patients. Diagnosis 
    and Management. A GINA Pocket Guide for Health Professionals. 2019.

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