Asthma

Asthma is a chronic inflammatory condition of the airways that causes episodic exacerbations of bronchoconstriction. Bronchoconstriction is where the smooth muscles of the airways (the bronchi) contract causing a reduction in the diameter of the airways. Narrowing of the airways causes an obstruction to airflow going in and out of the lungs. 

In asthma there is reversible airway obstruction that typically responds to bronchodilators such as salbutamol. This bronchoconstriction is caused by hypersensitivity of the airways and can be triggered by environmental factors.

Typical Triggers

• Infection
• Night time or early morning
• Exercise
• Animals
• Cold/damp
• Dust
• Strong emotions

Presentation Suggesting a Diagnosis of Asthma

• Episodic symptoms
• Diurnal variability. Typically worse at night.
• Dry cough with wheeze and shortness of breath
• A history of other atopic conditions such as eczema, hayfever and food allergies
• Family history
• Bilateral widespread “polyphonic” wheeze heard by a healthcare professional

Presentation Indicating a Diagnosis other than Asthma

• Wheeze related to coughs and colds more suggestive of viral induced wheeze
• Isolated or productive cough
• Normal investigations
• No response to treatment
• Unilateral wheeze. This suggests a focal lesion or infection.

Diagnosis

There is a difference in the guidelines on diagnosis. The British Thoracic Society (BTS) and SIGN guidelines from 2016 advise making a clinical diagnosis when there is a high clinical suspicion of asthma and testing when there is an intermediate or low clinical suspicion. The newer NICE guidelines from 2017 advise against making a diagnosis without definitive testing.

BTS/Sign Guidelines on Diagnosis

• High probability of asthma clinically: Try treatment
• Intermediate probability of asthma: Perform spirometry with reversibility testing
• Low probability of asthma: Consider referral and investigating for other causes

NICE Guidelines on Diagnosis

NICE recommend assessment and testing at a “diagnostic hub” to establish a diagnosis. They specifically advise not to make a diagnosis clinically and require testing:

First line investigations:

• Fractional exhaled nitric oxide
• Spirometry with bronchodilator reversibility

If there is diagnostic uncertainty after first line investigations these can be followed up with further testing:

• Peak flow variability measured by keeping a diary of peak flow measurements several times per day for 2 to 4 weeks
• Direct bronchial challenge test with histamine or methacholine

Long Term Management

There are key treatments for long term management of asthma:

Short acting beta 2 adrenergic receptor agonists, for example salbutamol. These work quickly but the effect only lasts for an hour or two. Adrenalin acts on the smooth muscles of the airways to cause relaxation. This results in dilatation of the bronchioles and improves the bronchoconstriction present in asthma. They are used as “reliever” or “rescue” medication during acute exacerbations of asthma when the airways are constricting.

Inhaled corticosteroids (ICS), for example beclometasone. These reduce the inflammation and reactivity of the airways. These are used as “maintenance” or “preventer” medications and are taken regularly even when well.

Long-acting beta 2 agonists (LABA), for example salmeterol. These work in the same way as short acting beta 2 agonists but have a much longer action.

Long-acting muscarinic antagonists (LAMA), for example tiotropium. These block the acetylcholine receptors. Acetylecholine receptors are stimulated by the parasympathetic nervous system and cause contraction of the bronchial smooth muscles. Blocking these receptors leads to bronchodilation.

Leukotriene receptor antagonists, for example montelukast. Leukotrienes are produced by the immune system and cause inflammation, bronchoconstriction and mucus secretion in the airways. Leukotriene receptor antagonists work by blocking the effects of leukotrienes.

Theophylline. This works by relaxing bronchial smooth muscle and reducing inflammation. Unfortunately it has a narrow therapeutic window and can be toxic in excess so monitoring plasma theophylline levels in the blood is required. This is done 5 days after starting treatment and 3 days after each dose changes.

Maintenance and Reliever Therapy (MART). This is a combination inhaler containing a low dose inhaled corticosteroid and a fast acting LABA. This replaces all other inhalers and the patient uses this single inhaler both regularly as a “preventer” and also as a “reliever” when they have symptoms.

Confusingly the new NICE guidelines are slightly different to the SIGN/BTS guidelines. The medications they recommend are the same but they differ slightly in the stepwise ladder of which medications to introduce at what point. Most importantly they both start with a short acting beta 2 agonist followed by a low dose inhaled corticosteroid. The next step is then either a leukotriene receptor antagonist or an inhaled LABA.

They principles of using the stepwise ladder are to:

• Start at the most appropriate step for the severity of the symptoms
• Review at regular intervals based on severity
• Step up and down the ladder based on symptoms
• Aim to achieve no symptoms or exacerbations on the lowest dose and number of treatments. This is often difficult in practice.
• Always check inhaler technique and adherence at review

BTS/SIGN Stepwise Ladder (adapted from 2016 guidelines)

1. Add short-acting beta 2 agonist inhaler (e.g. salbutamol) as required for infrequent wheezy episodes.
2. Add a regular low dose corticosteroid inhaler.
3. Add LABA inhaler (e.g. salmeterol). Continue the LABA only if the patient has a good response.
4. Consider a trial of an oral leukotriene receptor antagonist (i.e. montelukast), oral beta 2 agonist (i.e. oral salbutamol), oral theophylline or an inhaled LAMA (i.e. tiotropium).
5. Titrate inhaled corticosteroid up to “high dose”. Combine additional treatments from step 4. Refer to specialist.
6. Add oral steroids at the lowest dose possible to achieve good control.

NICE Guidelines (adapted from 2017 guidelines)

1. Add short-acting beta 2 agonist inhaler (e.g. salbutamol) as required for infrequent wheezy episodes.
2. Add a regular low dose inhaled corticosteroid.
3. Add an oral leukotriene receptor antagonist (i.e. montelukast).
4. Add LABA inhaler (e.g. salmeterol). Continue the LABA only if the patient has a good response.
5. Consider changing to a maintenance and reliever therapy (MART) regime.
6. Increase the inhaled corticosteroid to a “moderate dose”.
7. Consider increasing the inhaled corticosteroid dose to “high dose” or oral theophylline or an inhaled LAMA (e.g. tiotropium).
8. Refer to a specialist.

Additional Management

• Each patient should have an individual asthma self-management programme
• Yearly flu jab
• Yearly asthma review
• Advise exercise and avoid smoking

Last updated February 2019