Stress responsivity in children with externalizing behavior disorders.

Patterns of lower autonomic nervous system (ANS) and hypothalamic-pituitary-adrenal (HPA) axis activity have been found in children with oppositional defiant disorder (ODD). The aim of the present study was to investigate whether children with attention-deficit/hyperactivity disorder (ADHD) differ from ODD children with (OD/AD) or without comorbid ADHD in ANS and HPA axis activity under baseline and stressful conditions. The effects of stress on cortisol, heart rate (HR), and skin conductance level (SCL) were studied in 95 children (26 normal control [NC] children and 69 child psychiatric patients referred for externalizing behavior problems [15 ODD, 31 OD/AD, and 23 ADHD]). No baseline differences were found in cortisol between the four groups. However, the ODD and OD/AD groups showed a significantly weaker cortisol response to stress compared to the ADHD and NC groups; the ADHD group had a similar cortisol response as the NC group. Within the ODD group this pattern of low cortisol responsivity was most clearly present in the more severely affected inpatients. With respect to HR, the ODD group had a significantly lower HR during baseline and stressful conditions. The higher HR levels in the OD/AD and ADHD groups were likely to be caused by methylphenidate. The externalizing groups had significantly lower SCL levels, and no differences were found between these groups. It was concluded that differences in cortisol responsivity during stress exposure are important in distinguishing within a group of children with externalizing behavior between those with ODD and ADHD.