Heterogeneity of irritability in attention-deficit/hyperactivity disorder subjects with and without mood disorders

Background: We hypothesized that irritability is a heterogeneous symptom distinguished by severity and that attending to this heterogeneity would impact the relationship between irritability and bipolar disorder. Methods: A total of 274 ADHD children were administered the Kiddie Schedule for Affective Disorders and Schizophrenia (Epidemiologic Version) structured diagnostic interview. Three measures of irritability were identified: oppositional defiant disorder (ODD)-type irritability, mad/cranky irritability, and super-angry/grouchy/cranky irritability. Subjects were stratified as having bipolar disorder (n = 30), unipolar depression (n = 100), and no history of depression or bipolar disorder (non-mood-disordered, n = 144). Results: Oppositional defiant disorder-type irritability was very common in all ADHD subjects, was the least impairing, and did not increase the risk of mood disorder. Mad/cranky irritability was common in only ADHD children with a mood disorder, was more impairing than the ODD-type irritability, and was predictive of unipolar depression. Super-angry/grouchy/ cranky irritability was common only in ADHD children with bipolar disorder, was the most impairing, and was predictive of both unipolar depression and bipolar disorder. Two percent of the subjects with ODD-type irritability only, 6% of subjects with mad/cranky irritability, and 46% of subjects with super-angry/grouchy/cranky irritability were diagnosed with bipolar disorder. Conclusions: These results challenge the conclusion that irritability is necessarily a poor diagnostic indicator of bipolar disorder in children.