Disruptive Mood Dysregulation Disorder and Bipolar Disorder Not Otherwise Specified: Fraternal or Identical Twins?

Objective: The purpose of this study was to examine similarities and differences between disruptive mood dysregulation disorder (DMDD) and bipolar disorder not otherwise specified (BP-NOS) in baseline sociodemographic and clinical characteristics and 36 month course of irritability in children 6-12.9 years of age. Methods: A total of 140 children with DMDD and 77 children with BP-NOS from the Longitudinal Assessment of Manic Symptoms cohort were assessed at baseline, then reassessed every 6 months for 36 months. Results: Groups were similar on most sociodemographic and baseline clinical variables other than most unfiltered (i.e., interviewer-rated regardless of occurrence during a mood episode) Young Mania Rating Scale (YMRS) and parent-reported General Behavior Inventory-10 Item Mania (PGBI-10M) items. Children with DMDD received lower scores on every item (including irritability) except impaired insight; differences were significant except for sexual interest and disruptive-aggressive behavior. Children with DMDD received lower scores on eight of 10 PGBI-10M items, the other two items rated irritability. Youth with DMDD were significantly less likely to have a biological parent with a bipolar diagnosis than were youth with BP-NOS. Children with DMDD were more likely to be male and older than children with BP-NOS, both small effect sizes, but had nearly double the rate of disruptive behavior disorders (large effect). Caregiver ratings of irritability based on the Child and Adolescent Symptom Inventory-4R (CASI-4R) were comparable at baseline; the DMDD group had a small but significantly steeper decline in scores over 36 months relative to the BP-NOS group (b = -0.24, SE = 0.12, 95% CI -0.48 to -0.0004). Trajectories for both groups were fairly stable, in the midrange of possible scores. Conclusions: In a sample selected for elevated symptoms of mania, twice as many children were diagnosed with DMDD than with BP-NOS. Children with DMDD and BP-NOS are similar on most characteristics other than manic symptoms, per se, and parental history of bipolar disorder. Chronic irritability is common in both groups. Comprehensive evaluations are needed to diagnose appropriately. Clinicians should not assume that chronic irritability leads exclusively to a DMDD diagnosis.