With nearly a third of all children having a wheezing episode before their third birthday and half by age 6 years, wheezing is one of the most problems for which preschool children are seen in the pediatrician's office.1,2 Further, children who wheeze once are likely to wheeze again, making recurrent wheeze a frequent problem.
The problem for pediatricians is that although there are guidelines for asthma, not all that wheezes is asthma. Further, the medical literature has poorly defined a phenotypic difference the practicing pediatrician commonly sees—the otherwise healthy preschool child with a viral-induced wheezing event versus an asthma exacerbation triggered by a virus. The medical literature commonly cites epidemiologic criteria such as wheezing in the first 3 years of life, transient versus persistent wheeze, or atopic versus nonatopic, but these criteria are retrospective and do not help the practicing pediatrician in the office.1 Defining wheezing via temporal patterns may be more useful for the busy clinician.
Temporal patterns of wheezing
The European Respiratory Society Task Force recommends differentiating wheezing phenotypes that provide the pediatrician with some evidence that can assist with treatment into episodic viral wheezing and multiple-trigger wheezing.2
Episodic viral wheezing. Episodic viral wheezing is defined as wheezing during discrete time periods in an otherwise healthy child who is without symptoms between these episodes.2 Wheezing episodes are generally associated with a clinical diagnosis of viral upper respiratory tract infection (URTI). Rhinovirus, respiratory syncytial virus (RSV), coronavirus, human metapneumovirus, parainfluenza virus, and adenovirus are commonly cited in research studies that attempt to find a diagnosis, but this is not commonly done in clinical practice.2 Possible underlying factors include preexisting impaired lung function, tobacco smoke exposure, prematurity, and atopy.2,3
Repeat episodes commonly occur seasonally, and some children experience severe symptoms from these wheezing episodes. Factors identifying why the episodes recur and why the severity is increased in some preschoolers is poorly understood. In most children episodic viral wheezing declines over time, but it can persist into school age or become multiple-trigger wheezing.3
Multiple-trigger wheezing. Viral illness is not the only trigger for wheezing episodes, which can also include triggers such as smoke and pollen, among others. Patients in this category demonstrate symptoms between episodes. Although some believe multiple-trigger wheezing to be representative of a chronic inflammatory condition, there is limited evidence supporting this.2
Both phenotypes are lacking, however, in that they will not identify children who will go on to develop asthma, children who will outgrow their symptoms, or children who have bronchiolitis for which steroids are not indicated.1