Associations Between Autism-Related Characteristics and Tonic Versus Phasic Irritability Across Parent and Teacher Report.

OBJECTIVE: Irritability in youth is increasingly understood as comprising tonic irritability, reflecting persistent irritable mood, and phasic irritability, reflecting acute anger outbursts. This study examined whether these dimensions showed distinct associations with autistic characteristics across parent and teacher report. METHODS: Clinical records were examined for 1534 youth ages 5-18 referred to a university outpatient psychiatric clinic, including 334 youth with a PDD/ASD diagnosis. Analyses were conducted separately in the PDD/ASD-restricted sample (n = 334) and the full diagnostic sample (N = 1534). Multiple regression models examined associations of social interaction differences, communication differences, and restricted and repetitive behaviors (RRBs) with standardized tonic and phasic irritability, adjusting for the alternate irritability dimension, psychiatric diagnoses, age, and gender. RESULTS: RRBs were associated with parent-reported tonic and phasic irritability in both samples and with teacher-reported tonic and phasic irritability in the full diagnostic sample. Social interaction differences were more consistently associated with tonic than phasic irritability. Tonic irritability increased with age, whereas phasic irritability decreased with age across informants and samples. Psychiatric correlates varied by irritability dimension and informant. CONCLUSIONS: Tonic and phasic irritability showed overlapping but partially differentiated associations with autistic characteristics. RRBs were linked to both dimensions, whereas social interaction differences were more closely related to tonic irritability.