Medical Matters: Asthma is one of the commonest chronic diseases of affluent societies, affecting 10 per cent of children in the developed world and 5 per cent of people between the ages of 20 and 44.
The striking increase in asthma in recent decades and its rarity in less affluent populations suggests environmental factors are significant causes of the disease.
Asthma typically causes cough, wheeze and shortness of breath. These symptoms are principally due to inflammation and narrowing in the medium-sized airways in the lungs. Treatment is aimed at reopening the breathing tubes and reversing the inflammatory process.
Doctors increasingly work to disease-management guidelines, especially when they are treating chronic disease. The British Thoracic Society, which works in the interests of people with lung disease, produces respected guidelines for asthma; the latest version has recently been published, and it contains some changes.
The principal changes focus on the drug management of uncontrolled asthma in children. It is still a step-by-step management structure, but now it is divided into three age bands: under five years old, between five and 12, and over 12.
One of the key messages is that inhaled steroids are the most effective first-line preventive treatment for anybody with asthma, with the exception of those who have the mildest form of the disease.
Short-acting drugs such as Ventolin, which open up the breathing tubes, remain the treatment option for people with mild intermittent asthma symptoms. These "reliever" drugs are used only when required.
Treatment proceeds to step two if the patient needs to use his reliever inhaler more than twice a day or requires two or more refills a month. Persistent night-time symptoms or a worsening of asthma during exercise are other signs that it is time to step up treatment .
Standard doses of inhaled steroids are the cornerstone of "preventer" treatment in all three groups. But if standard dosages do not control symptoms, it is better for most patients to add another type of medication than to increase the dose of steroids.
The add-on drugs of choice in step three of treatment are an inhaled long- acting version of a reliever medication in the two older age categories; two- to five-year-olds benefit from what is called a leucotriene receptor agent. It is a new class of drug that was not available when the last set of guidelines was produced.
These receptor agents are given orally; single doses have been shown to open up the airways within an hour. Research suggests they also prevent the asthma from worsening.
In the face of persistent poor control of asthma symptoms, it is necessary to move to step four of treatment. For older children, this means trying a higher dose of inhaled steroid. Adults have a similar option, but some may also benefit from oral medication called theophyllines.
For children under five with persistent symptoms, however, it is time to consult a specialist in paediatric respiratory disease.
Step five of treatment for the older age categories basically consists of using oral steroids each day. It is not a step to be taken lightly, but for some people with severe asthma it is the only way of avoiding repeated hospitalisation.
The latest British Thoracic Society guidelines, which represent the consensus thinking of 130 healthcare professionals based on a review of more than 500 scientific references, include a section on asthma management in infants.
In the absence of objective measurement of lung function, which is impractical in such young children, management is based on the old-fashioned "trial of treatment" principle.
If there is a good response to inhaled Ventolin-like drugs and symptoms return when treatment is stopped, then the experts recommend regular inhaled steroid medication. It should be given through a face mask to overcome the co-ordination difficulties associated with the use of inhalers in infants.
The guidelines also contain useful prognostic indicators. Wheezing infants, for example, particularly those whose symptoms start young, have a good prognosis and are unlikely to develop lifelong asthma.
This column has concentrated solely on drug treatment. There are, of course, many non-drug interventions in the management of asthma. I am grateful to Dr Reggie Spelman, author of the Irish College of General Practitioners' asthma protocol, for his helpful interpretation of the latest guidelines.
You can e-mail Dr Muiris Houston at mhouston@irish-times.ie. He regrets he cannot answer individual queries