Asthma is a chronic inflammatory condition leading to obstruction of the small airways that is characteristically reversible.
Smooth muscle contraction, oedema and mucus production all contribute to the obstructive process. At a cellular level, eosinophilia, increased levels of IgE and the production of a variety of cytokines are features consistent with asthma. An estimated 6 per cent of the adult population have asthma, with late-onset asthma accounting for a significant minority of this total.
Normal spirometry does not rule out the possibility of asthma
A well-taken history is the key to diagnosing asthma. Recurrent cough, wheeze, chest tightness and shortness of breath are suggestive of asthma, with symptoms often worse at night or early morning, and aggravated by exercise. The characteristic finding in the chest is an expiratory wheeze, although absence of this does not exclude the diagnosis of asthma.
Atopic eczema and allergic rhinitis are related conditions, so a positive personal or family history of these conditions increases the probability of asthma. Cigarette smoke, environmental pollutants, cold air, respiratory tract infection and stress can all trigger asthma, and specific allergens such as animal proteins or pollen may also be implicated.
Measuring airway obstruction
Maintaining a peak flow diary over several weeks may demonstrate readings lower than predicted. A variation of 20 per cent or more in peak expiratory flow (PEF) rate points towards a diagnosis of asthma. Typically, PEF is highest in the afternoon and lowest in the early morning.
An improvement of 15 per cent in PEF within 30 minutes of administration of a short-acting beta-2 agonist, such as 400 micrograms of salbutamol, administered via a metered dose inhaler and spacer, is consistent with the reversible airway obstruction of asthma. An alternative positive test is a similar response in PEF to a two-week course of oral steroids, usually 30mg prednisolone daily in adults.
The recently updated British Thoracic Society (BTS)/SIGN guidelines recommend spirometry (FEV1 <80 per cent and an FEV1/FVC <70 per cent indicating obstruction) as the preferred test to assess the presence and severity of airflow obstruction. Normal spirometry in an asymptomatic individual does not however rule out the possibility of asthma.
On the basis of clinical features and measures of airway obstruction, BTS/SIGN recommend a diagnostic stratification to high, intermediate or low probability of asthma. For high probability cases a trial of treatment is recommended; for low probability cases investigation and treatment of the suspected diagnosis should be undertaken, referring on those cases where the diagnosis remains unclear.
For intermediate probability cases a trial of asthma treatment is reasonable, particularly if there is evidence of airway obstruction, but a poor response to treatment should prompt consideration of alternative diagnoses with appropriate investigation or referral.
The most common differential diagnosis in adults is COPD, where there is obstructive airway disease but a lack of reversibility of PEF or FEV1. It is possible for patients to have both asthma and COPD, and in these circumstances the safe course of action is that they should receive treatment for asthma, notably with inhaled corticosteroids.
Smoking cessation should be strongly encouraged and appropriate support and pharmacological help provided. Weight reduction in obese patients is recommended to improve the symptoms of asthma. The BTS/SIGN guidelines suggest breathing techniques as a method of symptom control.
If house dust mites are thought to be a problem then exposure can be minimised by vacuuming and reducing soft furnishings and carpets.
Animals such as cats and dogs should be kept out of the bedroom if they are a likely cause of asthma.
Certain drugs, notably beta-blockers, aspirin and NSAIDs can trigger or worsen asthma and should, if possible, be avoided or withdrawn. Annual influenzae vaccination and a single pneumococcal vaccination are recommended.
The aims of medical treatment of asthma are to control symptoms and to prevent exacerbations, while minimising possible side-effects, so that disturbance to lifestyle, work and exercise is reduced as far as possible.
The recently updated BTS/SIGN guidelines on the stepwise approach to treating asthma in adults are summarised in the box. Treatment is started at the step most appropriate to the severity of asthma and subsequently may be intensified or reduced according to response. The guideline also contains sections on management of acute asthma, work-related asthma and asthma in pregnancy.
Recent NICE guidelines report no difference in clinical effectiveness between various inhaled corticosteroids (ICSs). Ciclesonide and mometasone furoate are newer ICSs that offer the possibility of reduced systemic side-effects through lower bioavailability, and have the advantage of once-daily administration, which may aid compliance.
The long-acting beta-2 agonists (LABAs), salmeterol and formoterol, should not be used in asthma in the absence of ICSs as there is evidence to suggest that under these circumstances there is an increased rate of exacerbations and even fatalities. Addition of a LABA to an ICS has been shown to be superior to increasing the dose of ICS in terms of symptoms, lung function and reduction of exacerbations in asthmatics.
Compliance may be improved by using a combination inhaler containing an ICS and LABA and is endorsed by NICE.
There is evidence that the budesonide/formoterol combination inhaler can be used as both a regular maintenance and reliever therapy, and that this strategy (which relies on formoterol having a rapid onset of action) is superior in reducing exacerbations than using a maintenance ICS/LABA or high-dose ICS in combination with a short-acting beta-2 agonist. The BTS/SIGN group advise that this option could be used at step 3 of the guideline.
The leukotriene receptor antagonists, montelukast and zafirlukast, may be useful in asthmatic patients with co-existent allergic rhinitis.
Patient self-management plans have been demonstrated to improve asthma control, reduce hospital admissions and result in fewer days work lost. The BTS/SIGN guidelines recommend a personalised written action plan that allows the patient to identify warning signs of deteriorating asthma and to be able to react appropriately.
A symptom diary and peak flow readings are used to direct treatment and identify when to seek medical help.
- Dr Morris is a GP in Shrewsbury, Shropshire
Summary of BTS/SIGN guidelines on asthma
Step 1: Mild intermittent asthma
Inhaled short-acting beta-2 agonist as required.
Step 2: Regular preventer therapy
Add ICS at dosage appropriate to disease severity.
Step 3: Add-on therapy
Add inhaled LABA.
If LABA beneficial but control still inadequate, increase dosage of ICS.
If no response to LABA, stop LABA and increase dosage of ICS: if response still inadequate try alternative add-on therapy.
Step 4: Persistent poor control
Increase dosage of ICS further or add a fourth drug; for example, leukotriene receptor antagonist, slow-release theophylline, or oral beta-2 agonist.
Step 5: Use of oral steroids
Use daily oral steroids in lowest dosage possible providing adequate control.
Refer for specialist care.
Barnes P J. Using a combination inhaler (budesonide plus formoterol) as rescue therapy improves asthma control. BMJ 2007; 335: 513.