Background
Atopic dermatitis (AD) is a common chronic inflammatory skin disorder characterised by pruritus and recurrent eczematous skin lesions affecting up to 20% of children in high-income countries.1 Besides other atopic diseases such as allergic rhinitis, food allergies and asthma, children with AD are also more at risk for non-allergic comorbidities including infectious and systemic diseases, as well as neurodevelopmental disorders such as attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD).2–4 Current studies on paediatric AD focus on the clinical treatment of the disease but there are still gaps in knowledge regarding aforementioned neurodevelopmental comorbidities. Complex pathomechanisms, involving both genetic and environmental factors, combined with global increases in prevalence of AD, ADHD and ASD in the past decades has led to many hypotheses on the underlying etiological associations between these conditions.5–9
ADHD is one of the most common neurodevelopmental disorders in children, characterised by symptoms of inattention, hyperactivity and impulsivity.10 Children with ADHD often have sensory processing problems, which is the inability to effectively regulate and organise a graded and adaptive response to sensory stimuli.11–13 Similar to ADHD, children with AD also exhibit symptoms of altered sensory processing, expressing sensory hyporeactivity or hyper-reactivity compared with controls.14 15 Epidemiologically, individuals with AD are more at risk for ADHD with an estimated OR=1.32 (95% CI, 1.20 to 1.45) for all ages to OR=1.56 (95% CI, 1.38 to 1.77) in children and adolescents.16 17
ASD is a heterogeneous neurodevelopmental disorder, encompassing former diagnoses such as autistic disorder, Asperger syndrome and pervasive developmental disorder not otherwise specified.18 Traits displayed by diagnosed individuals include persistent difficulties with social communication and interaction, and the presence of restricted and repetitive patterns of behaviour from an early developmental period.18 19 Comparable to both AD and ADHD, children with ASD have also been found to have more sensory hyporeactivity or hyper-reactivity symptoms.20 The risk for developing ASD in individuals with AD has been estimated to be OR=1.49 (95% CI 1.20 to 1.83) in all ages to OR=2.57 (95% CI 1.47 to 4.51) in children and adolescents.17 21 Moreover, children with ASD with AD may have more pronounced ASD symptoms overall and on the social domain outcomes, relative to children with ASD without AD.22
Due to the parallel rises in the global prevalences of AD, ADHD and ASD, an increasing interest among many research groups emerges for the potential influence of atopic diseases on the skin–brain axis within the field of neurodevelopment.17 22 A positive association between paediatric AD and the neurodevelopmental disorders ADHD and ASD has consistently been found in epidemiologic studies,17 but studies on the underlying pathophysiological mechanisms are scarce, leaving an ambiguous underlying interplay between dermatological, neurodevelopmental, and behavioural elements.
Objectives
The main goal for this proposed scoping review is to provide an extensive overview on the shared symptomatology between paediatric AD, and ADHD and ASD, and to highlight knowledge gaps regarding this matter. Extracted data will be mapped according to the following research questions:
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What are mutual traits in AD, ADHD and ASD?
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What are current hypotheses for the shared symptomatology of AD, ADHD and ASD?
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What are gaps in the current evidence for a potential underlying shared aetiology of AD, ADHD and ASD?
This post was originally published on https://bmjopen.bmj.com