Characterization and Pathophysiology of Severe Mood and Behavioral Dysregulation in Children and Youth

Objective:

Irritability is a common and impairing clinical presentation in youth. Despite its significant public health impact, the clinical course and pathophysiology of irritability remains poorly understood. Chronic and severe irritability is the primary symptom of the new DSM-5 diagnosis, disruptive mood dysregulation disorder (DMDD), is an associated symptom of other pediatric disorders including Attention-Deficit/Hyperactivity Disorder (ADHD), and can be a clinical precursor to Major Depressive Disorder (MDD) and anxiety disorders. In addition, irritability is a trait distributed continuously in youth, thereby fitting well within the National Institute of Mental Health (NIMH) Research Domain Criteria (RDoC) initiative.

Clinically impairing irritability in children and adolescents began to gain more attention as interest grew in the diagnosis of pediatric bipolar disorder. Beginning in the 1990s, child psychiatry researchers suggested that while pediatric bipolar disorder can present with distinct episodes of mania or hypomania as in adults, the more typical pediatric presentation was chronic, severe irritability and hyperarousal symptoms. However, data collected under this protocol comprise a series of longitudinal, family, behavioral, and pathophysiological studies that differentiated classically defined episodic pediatric bipolar disorder from chronic irritability without distinct manic or hypomanic episodes. These findings are consistent with reports from other groups and meta-analyses.

Among the several strands of research designed to differentiate pediatric bipolar disorder from chronic irritability, longitudinal studies provide the strongest evidence that these two phenotypes are distinct. Children with chronic irritability are at elevated risk for later depression, but not manic episodes. Thus, youth with MDD (with and without prior DMDD) are an important comparison group to explore, and we are examining the developmental trajectory, phenomenology, behavioral correlates, and underlying neural mechanisms of chronic irritability and MDD in youth. Further, because irritability and ADHD symptoms are highly comorbid in youth, participants with ADHD are an important comparison group in our work on irritability.

The current translational model of irritability emphasizes the role of abnormal threat and reward processing, but also underlines the relevance of environmental factors in the emergence and maintenance of irritability. More precisely, it is assumed that irritable children experience environments, where rewards and punishments are inconsistently delivered leading to unintentional reinforcement of disruptive behavior through the parents. Reasons for this inconsistent parent behavior could be manifold spanning instrumental learning deficits and exaggerated responses to threat and frustrative non-reward in the parents themselves as well as lack of knowledge regarding learning principles and increased levels of stress. These factors might contribute to instrumental-learning deficits in the children increasing frequency and intensity of temper outbursts. Heightened levels of chronic irritability, another symptom of DMDD, might be more associated with features of the parent-child interaction. There is a rich literature within the framework of attachment theory showing that behavior of children with anxious-resistant insecure attachment is characterized by a general angry tone and is also associated with increased amygdala responses to negative social scenes. In addition, it was also shown that highly irritable infants are less sociable in terms of being less responsive and more fearful towards others and displaying an angry emotional tone in general as toddlers when they had been insecurely attached and more sociable when they had been securely attached. Adding another layer of complexity, it is also conceivable that inconsistent parent behavior diminishes parent's perceived trustworthiness. This could be of relevance as recent studies showed that persons are less willing to delay rewards - an action bound to increase levels of frustration - if their interaction partner is perceived as little reliable.