1. Epidemiology and aetiology
Wheezing occurs in 25–35 per cent of preschool children but, in about 60 per cent of them, this tendency ceases by six years and in 80 per cent by 10 years. In epidemiological studies this condition is termed ‘transient wheeze’.
As a group there is no increase in atopic disease or a family history of asthma, but the tendency to wheeze is increased in those whose mothers smoke. This is in contrast to ‘persistent wheeze’, when children continue to wheeze beyond three years of age, a situation strongly linked to a personal or family history of allergy. The distinction between the two is only possible retrospectively.
It can difficult to distinguish between wheeze (a whistling sound caused by airway narrowing), mucus in the airway or even stridor, particularly as all respiratory noises are exacerbated by respiratory viral infections. Airway narrowing related to virus infections is caused by mucosal swelling due to acute inflammation and this is likely to cause symptoms in those with smaller or more reactive airways, due to interuterine or familial factors.
In those wheezing only in response to virus infections (viral wheeze) there is no chronic airway inflammation.
Airway sensitisation to allergens increases with age in those who are susceptible. This results in a chronic eosinophilic airway inflammation, which increases airway reactivity so that symptoms may occur in response to multiple triggers (crying, laughter, exercise, cold air, allergen exposure and so on) as well as viruses. This is called asthma or multiple wheeze.
The pattern of viral wheeze is of episodic wheeze and cough associated with respiratory virus infections, with completely symptom-free periods.
There is a wide spectrum of presentation, ranging from a single episode of mild cough and wheeze to frequent and distressing episodes associated with tachypnoea and rib recession.
In asthma or multiple wheeze there is a range of severity and frequency of symptoms but by definition, symptoms occur also in the absence of a viral infection, so that the child wheezes in response to multiple triggers.
Many young children who develop this pattern exhibit only viral wheeze in the first few years of life and their symptoms are, at that stage, indistinguishable from those of transient viral wheeze.
Multiple attacks, hospitalisation for acute early wheeze and allergy are risk factors for developing asthma. Even so, prognosis is difficult to predict accurately in an individual. There are no objective tests or investigations to help diagnose either viral wheeze or multiple wheeze, which are diagnosed by history and observation.
Difficult to diagnose
Viral wheeze can be quite difficult to diagnose in young children because many respiratory sounds, such as increased airway mucus and stridor, can be confused with wheezing by parents or even healthcare professionals. Also other respiratory noises are exacerbated by respiratory infections and are associated with cough.
Significant airflow obstruction produces lower rib recession and tachypnoea. Characteristically, there are no symptoms between respiratory infections. Other diagnoses should be considered if the child is failing to thrive or has severe or recurrent pneumonia.
Asthma or multiple wheeze
The term asthma is used in many ways, from any bronchodilator-responsive wheeze to a specific kind of wheeze associated with allergy. There is no agreed definition but, for practical reasons, it is helpful to use the term for wheeze that occurs in response to multiple triggers, either with or without attacks related to virus infections.
The reason for this is there is no evidence that other patterns of wheeze respond to anti-inflammatory therapy. Nevertheless, it should be appreciated that a child with viral wheeze can develop asthma as school age approaches.
A key sign is wheezing on exercise in the absence of a cold or infection. The occasional child develops allergic airway sensitisation in infancy and wheezes between acute episodes, on crying for example (infant exercise). This indicates a high degree of allergy, or allergen exposure (for example, to a pet), which is usually apparent.
Management of preschool wheeze was not specifically considered in the BTS/SIGN guidelines 2005.
This very common condition is least responsive to treatment in children under the age of two years.
Bronchodilators have not been shown to work in children younger than 18 months although, anecdotally, some parents claim benefit. Bronchodilators given by masked spacers work in children older than two years. It is important to demonstrate correct spacer use and many babies have difficulty using them at first.
A modest benefit is seen when inhaled corticosteroids (ICS) are given with a masked spacer as a short-term, high-dose treatment. However, ICS do not work as prevention in this condition at any age, even in those with atopy and a strong family history of asthma.
Montelukast is the most promising approach. It can be given regularly, but may be unnecessary for an intermittent condition not associated with chronic airway inflammation. It has been shown to be effective when given at the onset of a viral-induced exacerbation. No trials have targeted children under two years, but it is worth trying.
In children over two years, beta-agonists are first-line treatment and if symptoms are more troublesome or frequent, montelukast should be added. Parents who smoke should be encouraged to stop smoking in front of their child. Children with asthma or allergy in the family are at risk of developing asthma as they grow older.
Asthma or multiple wheeze
Beta-agonists are first-line treatment, but if they are needed more than three times a week for prolonged periods, anti-inflammatory treatment is indicated. Asthma or multiple wheeze responds well to continuous anti-inflammatory treatment. Montelukast is worth trying if the child rejects the spacer. In severe cases a long-acting beta-agonist can be added.