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.