Written by Sarah Lee
Last Reviewed: April 2019
Review Due: April 2020
‘a chronic inflammatory disease of the airways that is characterised by bronchial hyperresponsiveness and reversible airflow obstruction resulting in recurrent episodes of breathlessness, cough, chest tightness and wheeze that is often made worse by specific triggers’
Complex interactions between genetic and environmental factors are thought to contribute to the development of asthma:
Many genes are associated with the condition
A strong family history is very significant
Smoking during pregnancy/secondary exposure
Viral - Rhinovirus, Influenza Virus, Respiratory Syncytial Virus etc
Bacterial - Mycoplasma Pneumoniae, Chlamydia Pneumoniae etc
Triad of Atopy
History of eczema, atopic dermatitis, allergic rhinitis
Exposure to Allergens
Common Allergens: animal fur, dust mites, pollen, moulds
Occupational Allergens: flour, dusts, chemicals
SIGNS AND SYMPTOMS
Cough (often nocturnal)
Sputum Production (yellow)
Widespread wheeze on auscultation
Respiratory Tract Infections
Drugs (e.g. NSAIDs, Beta Blockers)
PATTERN OF CLINICAL PRESENTATION
Diurnal Variation - symptoms worse at night/early morning
Worsens in the presence of precipitants, improves when removed
Patients may complain of disturbed sleep and days off school/work
1. Airway Inflammation
Exposure to allergen triggers an IgE-mediated Type 1 hypersensitivity reaction within the lungs.
Mast cell degranulation and production of inflammatory mediators (eg histamine, leukotrines) and cytokines (eg Il-4, IL-5) occurs.
Inflammatory cells including eosinophils migrate to airways produce more mediators, propagating the inflammatory response.
2. Airway Obstruction
Inflammation causes bronchospasm, mucosal oedema and increased mucus secretion within airways.
Chronic inflammation may cause bronchial smooth muscle hypertrophy and airway remodelling over time which may cause airflow limitations to be only partially reversible.
3. Bronchial Hyperresponsiveness
Eosinophil products increase resting tone of bronchial smooth muscle.
Bronchi become hyperresponsive and produce a larger response, more quickly to the allergen on the next exposure.
Gold standard diagnostic test for asthma
Should show an obstructive pattern (i.e. FEV1:FVC <0.7)
Must also show reversibility (at least 15% improvement) after bronchodilator
Peak Expiratory Flow (PEF)
PEF in asthmatic patients is typically lower than expected for the patient's height, age and gender
Monitoring and recording PEF can help establish variability, triggers and efficacy of medicine
Normal or Eosinophilia
May show hyperinflation in chronic asthma
Identify and avoid precipitants
Reduce exposure to cigarette smoke
Breathing exercises (physiotherapist-taught)
Guidelines from the British Thoracic Society and Scottish Intercollegiate Guidelines Network suggest the best approach to the long-term management of asthma. They recommend a five-step approach, that can be escalated or de-escalated as guided by the patient's symptoms. Guidelines for the management of asthma in children follow a similar approach.
Common classes of drugs used in the management of asthma include:
Short Acting Beta2 Agonists/SABA (e.g. Salbutamol)
Long Acting Beta2 Agonists/LABA (e.g. Salmeterol)
Inhaled Corticosteroids (e.g. Beclometasone)
Leukotriene Receptor Antagonists (e.g. Montelukast)
Asthma affects more than 30 million people in Europe with an estimated 8 million (12% of the population) in the UK having a diagnosis of asthma.
Oxford Handbook of Clinical Medicine (pages 178-182)