(PS2-D99) Parsing the Relationship Between Irritability, ADHD Symptoms, and Inhibitory Control: A Latent Variable Approach

Irritability is a heterogeneous construct characterized by both phasic (i.e., temper outbursts) and tonic (i.e., grumpy mood) dimensions. Elevated irritability is present in numerous psychiatric disorders, including disruptive mood dysregulation disorder (DMDD) and attention-deficit/hyperactivity disorder (ADHD). Prior research has found that phasic and tonic irritability are dissociable constructs through differential associations with ADHD symptoms. At the same time, extant literature has shown that deficits in inhibitory control may underlie ADHD and its externalizing features, suggesting that an investigation of inhibitory control as a mechanism facilitating differential associations between irritability symptoms and ADHD is warranted.

A transdiagnostic sample of 141 youth (M age=12.28[2.43], 45.6% female) with a primary diagnosis of DMDD, ADHD, or no diagnosis, were invited to complete four canonical response inhibition tasks. Task performance was assessed through a latent factor of inhibitory control performance estimated from a measured variable across each task using confirmatory factor analysis (CFA). Consistent with prior work, tonic and phasic irritability were measured via independent CFAs estimating latent factors of phasic irritability, tonic irritability, and aggression using items and/or subscales from selected parent-, self-, and clinician-report questionnaires (i.e., Affective Reactivity Index, Screen for Children’s Affective Reactivity – Home, State-Trait Anger Expression Inventory – Child/Adolescent, Retrospective Modified Overt Aggression Scale, and the Kiddie Schedule for Affective Disorders and Schizophrenia DMDD Module). ADHD symptoms were measured using the Conners Comprehensive Behavior Rating Scale.

Fit indices indicated good model fit for inhibitory control (CFI=1.00; TLI=1.00; RMSEA=0.00, CI90= [0.00–0.12]), phasic irritability (CFI=0.99; TLI=0.98; RMSEA=0.03, CI90= [0.00–0.06]), tonic irritability (CFI=0.99; TLI=0.99; RMSEA=0.04, CI90= [0.00–0.08]), and aggression (CFI=1.00; TLI=1.01; RMSEA=0.00, CI90= [0.00–0.06]). Factor scores for each participant were extracted to examine relations between irritability and aggression with inhibitory control. In line with prior work, ADHD was associated with impaired inhibitory control (r=-.41, p< .001) as well as higher aggression (r=0.24, p=.014) and phasic irritability (r=.20, p=.024), but not tonic irritability. Partial correlations controlling for ADHD symptoms found that only phasic irritability (r=-.28, p=.005), but not tonic irritability nor aggression, was associated with impaired inhibitory control. Further, only the association between inhibitory control and ADHD remained after accounting for comorbid phasic irritability and age (b=-.014, p=.002).

Results support the use of latent factor approaches to extract shared constructs underlying inhibitory control and further demonstrate that phasic and tonic irritability are dissociable through their differential associations with ADHD symptoms. Results also provide preliminary evidence that inhibitory control may represent a unique mechanism underlying ADHD symptoms even in the context of clinical levels of comorbid irritability.