Severe irritability is among the main reasons children and their families seek child mental health services. In 2013, children presenting with chronic irritability and frequent temper outbursts were given a diagnosis in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) termed disruptive mood dysregulation disorder (DMDD). However, even ten years later, there are few effective treatments. Understanding the mechanisms that cause or maintain DMDD is necessary to guide treatment development. The present thesis investigates executive functions (EFs), social cognition, and biological stress responses over time as potential factors contributing to DMDD. The EFs and social cognition of children with DMDD were compared to those of children with attention-deficit/hyperactivity disorder (ADHD) or oppositional defiant disorder (ODD) because these disorders often overlap. In Norway, 218 children (aged 6–12 years) referred to child mental health services completed neuropsychological tasks. Sixty-seven children also provided hair samples, which were analyzed for cortisol concentrations. Diagnostic interviews based on the DSM-5 were completed with their caregivers who also completed questionnaires.
First, the EFs of children with DMDD were assessed and compared to that of children with ADHD, ODD, or DMDD+ADHD and with normative values including clinical cutoffs. Regardless of diagnoses, the correlations between irritability and EFs were measured. Second, the social cognitive skills of children with DMDD were compared with normative values and with those of children with ODD. Moreover, the effect of EFs and social cognition on the social difficulties of children with DMDD or ODD was examined. Finally, as a measure of hypothalamic-pituitary-adrenal (HPA) axis activity over time (i.e., stress regulation), the hair cortisol concentrations (HCC) of children with DMDD, those with other types of psychological disorders, and healthy controls was compared.
The results indicate that children with DMDD have difficulties with central EFs, especially emotion control (EC) and cognitive flexibility (CF) in daily life. Similarly, higher irritability levels regardless of diagnoses were strongly and moderately correlated with worse EC and CF, respectively. Children with DMDD did not show difficulties with inhibition or working memory as reported by parents unless they also have ADHD (Paper I). However, more children with DMDD than the general population demonstrated difficulties with inhibition according to task performance (Paper II). No difference in EFs was observed between those with DMDD and ODD (Paper I). Children with DMDD or ODD displayed difficulties with understanding BRÆNDEN PHD THESIS APRIL 2023 others’ mental states and emotions but not with recognizing face emotions. In those with DMDD, EFs – but not social cognition – influenced social difficulties in daily life, with worse EFs being associated with increased social problems. In children with ODD, an interaction between EFs and social cognition influenced their social difficulties such that, if they displayed high difficulty with understanding others’ mental states and emotions, better EFs was associated with more social problems (Paper II). Finally, children with DMDD showed significantly higher HCC than those without psychological disorders (large effect size) but had HCC comparable to that of children with other types of psychological disorders (Paper III).
Based on the present findings and previous research, potential key mechanisms of DMDD, including their difference from central mechanisms of ADHD or ODD, are discussed. The results indicate that many children diagnosed with DMDD (a) have problems with flexibly stopping or shifting emotion regulation strategies, (b) have difficulties with understanding the mental states and emotions of others, and (c) have dysregulated stress (i.e., HPA) responses over time as indexed by a biological marker. These cognitive and biological factors may influence each other. The thesis also makes a broader contribution to the field of child mental health research by addressing how prolonged dysregulated HPA axis activity could be related to or an indicator of psychological disorders in children. Finally, implications for clinical practice and opportunities for future research are discussed.