Introduction

Asthma is the most common chronic respiratory disorder encountered in clinical practice. It affects over 10% of children and around 5-10% of adults, with the prevalence of asthma increasing. Not only does asthma account for a significant morbidity burden it should be remembered that around 1,000 people die in a year from asthma in the UK, 30-40 of whom are children.

Epidemiology

  • Incidence: 1000.00 cases per 100,000 person-years
  • Peak incidence: 20-30 years
  • Sex ratio: 1:1
Condition Relative
incidence
Asthma in adults1
Bronchiectasis0.02
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Aetiology

A number of factors can increase the risk of a person developing asthma:
  • personal or family history of atopy
  • antenatal factors: maternal smoking, viral infection during pregnancy (especially RSV)
  • low birth weight
  • not being breastfed
  • maternal smoking around child
  • exposure to high concentrations of allergens (e.g. house dust mite)
  • air pollution
  • 'hygiene hypothesis': studies show an increased risk of asthma and other allergic conditions in developed countries. Reduced exposure to infectious agents in childhood prevents normal development of the immune system resulting in a Th2 predominant response

Focusing on atopy, patients with asthma also suffer from other IgE-mediated atopic conditions such as:
  • atopic dermatitis (eczema)
  • allergic rhinitis (hay fever)

A number of patients with asthma are sensitive to aspirin. Patients who are most sensitive to asthma often suffer from nasal polyps. Remember the nose is part of the respiratory tract from a histological point of view.

Finally, around 10-15% of adult asthma cases are related to allergens in the workplace. Occupational asthma is usually diagnosed by observing reduced peak flows during the working week with normal readings when not at work. Examples of common occupational allergens include isocyanates and flour.

Pathophysiology

Asthma may be defined as a chronic inflammatory disorder of the airways secondary to type 1 hypersensitivity. The symptoms are variable and recurring and manifest as reversible bronchospasm resulting in airway obstruction.

Asthma may present at any age although it typically develops in childhood. For many of these children their symptoms improve or resolve with age, and patients often report 'growing out' of their childhood asthma. It should be remembered that it is common for young children to wheeze when they develop a virus ('viral-induced wheeze'). This makes the diagnosis of asthma in younger children difficult.

Clinical features

Symptoms

Signs
  • expiratory wheeze on auscultation
  • reduced peak expiratory flow rate (PEFR)

Investigations

NICE released guidance on the management of asthma in 2017. These followed on quickly from the 2016 British Thoracic Society (BTS) guidelines. Given previous precedents where specialist societies or Royal colleges eventually default/contribute to NICE, we have followed the NICE guidance for the notes and questions.

NICE guidance has radically changed how asthma should be diagnosed. It advocates moving anyway from subjective/clinical judgements are more towards objective tests.

There is particular emphasis on the use of fractional exhaled nitric oxide (FeNO). Nitric oxide is produced by 3 types of nitric oxide synthases (NOS). One of the types is inducible (iNOS) and levels tend to rise in inflammatory cells, particularly eosinophils. Levels of NO therefore typically correlate with levels of inflammation.

Other more established objective tests such as spirometry and peak flow variability are still important.

All patients >= 5 years should have objective tests. Once a child with suspected asthma reaches the age of 5 years objective tests should be performed to confirm the diagnosis.

Diagnostic testing

Patients >= 17 years
  • patients should be asked if their symptoms are better on days away from work/during holidays. If so, patients should be referred to a specialist as possible occupational asthma
  • all patients should have spirometry with a bronchodilator reversibility (BDR) test
  • all patients should have a FeNO test

Patients 5-16 years
  • all patients should have spirometry with a bronchodilator reversibility (BDR) test
  • a FeNO test should be requested if there is normal spirometry or obstructive spirometry with a negative bronchodilator reversibility (BDR) test

Patients < 5 years
- diagnosis should be made on clinical judgement

Specific points about the tests

FeNO
  • in adults level of >= 40 parts per billion (ppb) is considered positive
  • in children a level of >= 35 parts per billion (ppb) is considered positive

Spirometry
  • FEV1/FVC ratio less than 70% (or below the lower limit of normal if this value is available) is considered obstructive

Reversibility testing
  • in adults, a positive test is indicated by an improvement in FEV1 of 12% or more and increase in volume of 200 ml or more
  • in children, a positive test is indicated by an improvement in FEV1 of 12% or more

Management

NICE released guidance on the management of asthma in 2017. These followed on quickly from the 2016 British Thoracic Society (BTS) guidelines. Given previous precedents where specialist societies or Royal colleges eventually default/contribute to NICE, we have followed the NICE guidance for the notes and questions.

One of the key changes is in 'step 3' - patients on a SABA + ICS whose asthma is not well controlled should be offered a leukotriene receptor antagonist, not a LABA

NICE do not follow the stepwise approach of the previous BTS guidelines. However, to try to make the guidelines easier to follow we've added our own steps:

StepNotes
1

Newly-diagnosed asthma
Short-acting beta agonist (SABA)
2

Not controlled on previous step
OR
Newly-diagnosed asthma with symptoms >= 3 / week or night-time waking
SABA + low-dose inhaled corticosteroid (ICS)
3SABA + low-dose ICS + leukotriene receptor antagonist (LTRA)
4SABA + low-dose ICS + long-acting beta agonist (LABA)

Continue LTRA depending on patient's response to LTRA
5SABA +/- LTRA

Switch ICS/LABA for a maintenance and reliever therapy (MART), that includes a low-dose ICS
6SABA +/- LTRA + medium-dose ICS MART

OR consider changing back to a fixed-dose of a moderate-dose ICS and a separate LABA
7SABA +/- LTRA + one of the following options:
  • increase ICS to high-dose (only as part of a fixed-dose regime, not as a MART)
  • a trial of an additional drug (for example, a long-acting muscarinic receptor antagonist or theophylline)
  • seeking advice from a healthcare professional with expertise in asthma

Maintenance and reliever therapy (MART)
  • a form of combined ICS and LABA treatment in which a single inhaler, containing both ICS and a fast-acting LABA, is used for both daily maintenance therapy and the relief of symptoms as required
  • MART is only available for ICS and LABA combinations in which the LABA has a fast-acting component (for example, formoterol)

It should be noted that NICE does not advocate changing treatment in patients who have well-controlled asthma simply to adhere to the latest guidance.

Table showing examples of inhaled corticosteroid doses

Frustratingly, the definitions of what constitutes a low, moderate or high-dose ICS have also changed. For adults:
  • <= 400 micrograms budesonide or equivalent = low dose
  • 400 micrograms - 800 micrograms budesonide or equivalent = moderate dose
  • > 800 micrograms budesonide or equivalent= high dose.