Preschool wheeze (PSW) has now been recognised as a distinct wheezing entity and recent research has set about the difficult task of classifying wheezing phenotypes in preschool children in order to improve treatment modalities and attempt to predict those who will develop persistent asthma later in childhood. 

To date, these attempts have proved challenging but not wholly unrewarding. One may ask why bother differentiating between PSW and asthma at all. It is important to realise that young preschool children have smaller airways and lung volumes compared to older children and adults, thus their airways are more susceptible to collapse and obstruction with mucous secretions and swelling.

There is no diagnostic test for PSW or asthma so it is important that as clinicians we take a proper history. 

Historically, there has been little evidence for the use of asthma therapies in this age group, which has made the management of this condition trickier. However, recent studies have helped clear some of the fog surrounding the management of PSW. 

Classification of preschool wheeze

Different classifications of asthma in early childhood have been proposed following results from a number of longitudinal birth cohorts.^1,2,3,4 Some authors have argued that their use in everyday clinical practice is limited as the groups were analysed longitudinally and phenotypes designated retrospectively.⁵

In 2008, a European Respiratory Society (ERS) task force proposed that wheezing in preschool children be divided into two patterns of wheeze: episodic viral wheeze (EVW) or multiple-trigger wheeze (MTW).⁶

EVW was defined as: “Wheezing during discrete time periods, often in association with clinical evidence of a viral cold, with absence of wheeze between episodes.” 

MTW was defined as: “Wheezing that shows discrete exacerbations, but also symptoms between episodes.” The group also recommended that the term “asthma” should not be used in preschool children because the vast majority of them do not wheeze past the age of six years. 

With this new classification of PSW the researchers hoped that it would lead to improved clinical trials and treatment options for this population. 

Recent experimental evidence demonstrated lower pulmonary function in preschool children with MTW rather than EVW, supporting the division of the two phenotypes.⁷

Diagnosis of preschool wheeze

PSW is characterised by recurrent episodes of cough, wheezing, shortness of breath and chest tightness. 

Viruses, in particular human rhinovirus, account for the majority of wheezing exacerbations in preschool children.⁸

Other triggers, such as dust allergy, tobacco smoke, exercise and cold air, are less common causes of exacerbations in this age group. 

In order to choose the correct treatment option, in addition to ascertaining the timing and frequency of these episodes, it is essential to ask about a family history of atopy or asthma, a personal history of eczema or allergies, current and past tobacco smoke exposure and other environmental exposures such as carpets and pets. 

Preschool children with recurrent wheezing and atopy on a background parental history of asthma are more likely to have persistent asthma in later childhood.⁹ It is important to realise that not all wheezes are PSW or asthma and a different diagnosis must be considered in children who wheeze in an atypical pattern. 

Children with symptoms developing shortly after birth, continuous wheeze or wheezing not associated with triggers, failure to thrive, recurrent cough and loose stools or a poor response to asthma treatments should be referred onto a paediatric respiratory physician for specialist opinion. 

On examination, physical signs such as falling growth centiles, clubbing or unilateral wheeze on auscultation should signal alarm bells for clinicians. A common mistake by clinicians when diagnosing PSW is to mix up “wheezes” and “rattles”.  

“Wheeze” is often defined as high-pitched sound with a musical quality and is a sign of expiratory airflow limitation in the lower airways, whereas “rattles” are coarse respiratory sounds, which are lower in pitch and reflect a build-up of secretions in the upper airways. Parents often report feeling this noise as it vibrates over their child’s back.

Investigations in this age group should be limited as they are generally unhelpful in reaching a diagnosis. However, baseline investigations should include chest radiography to rule out congenital lung lesions or inhaled foreign bodies, full blood count for eosinophilia and sensitisation testing for common allergens which trigger wheezing exacerbations (house dust mite, grass pollen, mould and pets). 

With regard to pulmonary function testing, preschool children are generally not able to perform standard spirometry testing and, despite its use in many algorithms and guidelines for paediatric asthma, there is no evidence that peak expiratory flow rates (PEFR) improve asthma management.¹⁰

Management of PSW

A number of different treatment options are available for the management of PSW. Because of the heterogeneity of PSW, in the differences in wheezing patterns, severity of attacks and responses to different treatments, devising guidelines from current research has proved difficult.

Primary prevention

Primary prevention measures such as reducing exposure to tobacco smoke and aeroallergens have been examined in the literature. While there is compelling evidence that maternal smoking is strongly associated with an increased risk of asthma in early childhood,⁴ the argument for aeroallergen avoidance is less convincing. 

A recent Cochrane review concluded that interventions resulting in avoidance of single aeroallergens are ineffective.¹¹

Interventions that focused on multiple allergens, including food allergens, fared better but the evidence was not conclusive. Avoidance of multiple allergen exposures is both an expensive and time-consuming process that should only be reserved for very high-risk children.

Education

Education of parents on correct inhaler and spacer technique and distribution of asthma action plans has been shown to improve compliance and decrease healthcare visits. 

Multiple education sessions for the parents of preschool children are often needed and it is important to ask about inhaler technique and compliance at follow-up visits. 

Acute management

For the management of an acute wheezing episode in the community, inhaled bronchodilators via an age-specific spacer device remains the cornerstone of treatment. However, it must be recognised that not all children with PSW respond to bronchodilator treatment and the response to treatment should be assessed and documented. 

The evidence for oral corticosteroids (OCS) in the management of acute PSW is inconsistent. A Cochrane review published in 2003 demonstrated that OCS decreased the length of stay in hospital for children admitted with acute asthma.¹² However, no study specifically analysing PSW was included in this review. 

Since this publication, a large randomised controlled trial examining the role of OCS in preschool children hospitalised with acute viral wheeze demonstrated no decrease in inpatient length of stay.¹³ Also, there is no evidence that parent-initiated treatment with OCS at the onset of acute viral wheeze is of any clinical benefit.¹⁴ 

Generally, a trial of OCS is warranted in high-risk children suffering from severe episodic viral wheeze requiring hospitalisation but their role in preschool children with milder episodic wheeze is less clear.

Chronic management

Children who experience minimal wheezing symptoms with URTIs on an infrequent basis can usually just be managed with inhaled bronchodilators given over the course of the acute illness.

It is generally agreed that if a child is experiencing significant wheezing symptoms either with or without upper respiratory tract infections (URTIs) on a frequent basis, then a preventative medication should be considered. 

The best preventative measure to prescribe for PSW is still not agreed upon. A number of studies have examined the role of intermittent and regular asthma controllers and used the ERS classification, namely EVW and MTW, to differentiate between PSW phenotypes. 

A recent study examined the role of intermittent high-dose inhaled corticosteroids (ICS) during an acute wheezing episode in preschool children and demonstrated a clear reduction in the need for rescue oral corticosteroids but had an adverse effect on linear growth.¹⁵

A short seven-day course of montelukast at the onset of an acute viral wheezing episode has been shown to result in a 30% reduction of unscheduled healthcare visits.¹⁶ Therefore, given the lack of associated systemic side-effects, montelukast could be considered as an intermittent treatment option for preschool children with EVW. 

With regard to maintenance treatment, there is evidence that daily treatment with either ICS or montelukast reduces wheezing episodes in preschool children with MTW.^17,18 However, the evidence is less clear for children with EVW. 

Generally, a trial of an ICS is warranted in preschool children with troublesome intermittent symptoms occurring on a frequent basis, especially those at high risk of developing persistent asthma.⁶

The child’s response to treatment should be reassessed after three months and the decision to continue with the treatment should be monitored on an ongoing basis. 

The asthma phenotypes expressed by children, especially in the preschool category, often change over time.¹⁹ Most EVW in children tends to decrease in frequency with age and one study demonstrated that 60% of children who wheeze in the first three years of life have stopped by the age of six.⁴

Although some wheeze episodically throughout childhood or go on to develop persistent asthma, identifying which children fall into which outcome category in clinical practice has proved difficult and should be the focus of future research.

Conclusion

Preschool wheezing is a distinct wheezing entity that requires a specific management approach. Some progress has been made on deciding how best to categorise and manage these children in clinical practice. 

Further scientific evidence is required to validate the current classification system and further our knowledge on treatment strategies.  

References

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