Introduction
Wheezing in preschool children results in significant morbidity and
healthcare costs worldwide[1-3]. Prevention of acute symptoms and
hospitalisation is challenging because it is a heterogeneous disease,
and little is known about the pathophysiological mechanisms underlying
different phenotypes. However, there is good evidence that preschool
wheezers with a phenotype that fits with “persistent asthma”,
characterised by recurrent and persistent wheezing, associated with a
history of atopy in the child or immediate family, respond to
maintenance inhaled corticosteroids (ICS) with a reduction in
exacerbations and improved symptom control[4, 5]. Children with a
clinical phenotype of multiple trigger wheeze (wheeze during and between
episodes) are also considered more steroid responsive than those with
only episodic viral wheeze[6]. In addition, preschool wheezers with
either or both of aeroallergen sensitisation and elevated blood
eosinophils are thought to respond to ICS[7]. Although the efficacy
of maintenance ICS has been assessed in specific phenotypes in the
context of clinical trials, little is known about the relationship
between adherence to prescribed ICS and efficacy in preschool children
with troublesome wheeze in the clinic.
Adherence to maintenance ICS in school age children ranged from
20%[8] up to 74%[9], and higher adherence was associated with
better asthma control. In younger children aged (2-6 years) with
wheeze/asthma, objectively monitored adherence for 12 months was
reported as a median of 87% and >80% adherence was
associated with better symptom control assessed using the asthma control
questionnaire[10]. In another study that included young children (18
months – 7 years), median adherence rate was 71% with a range of
21-100%[11]. Both studies that included young children used
electronic monitoring devices (Smartinhalers) to assess adherence.
However, neither reported the impact of adherence on symptom control in
children with an objective phenotype that is likely responsive to ICS.
Much of the data that has shown relationships between objective
monitoring of adherence and asthma control in school-age children has
been in difficult asthma, the majority of such patients having allergic,
eosinophilic disease which is steroid responsive. However, preschool
wheezers may not all have an ICS responsive phenotype. Monitoring
adherence to prescribed ICS may be beneficial in wheezers to help
identify those with a steroid responsive phenotype. The impact of
adherence to prescribed ICS in a population of preschool children with
severe recurrent wheeze has not previously been reported. We
hypothesised that firstly, adherence to prescribed ICS would be higher
in children with severe preschool wheeze attending a specialist
paediatric respiratory clinic compared to published data in school-age
children with difficult asthma and secondly, that a period of adherence
monitoring would result in improved symptom control only in those with
ICS responsive features (multiple trigger wheeze or aeroallergen
sensitisation). We investigated adherence to ICS using electronic
monitoring devices for 4 months and related this to symptoms, offline
exhaled nitric oxide (FeNO), quality of life and unscheduled healthcare
visits in children aged 1-5 years with recurrent, troublesome preschool
wheeze.