Dysthymic disorder contributes to oppositional defiant behaviour in children with Attention Deficit Hyperactivity Disorder, combined type (ADHD-CT).

BACKGROUND: The specific relationships between oppositional defiant disorder (ODD), ADHD-CT, dysthymic disorder (DD) and anxiety disorders symptoms have not been studied in children with ADHD-CT. The relationship to DD is important because DD is common, has an earlier age of onset, is associated with significant morbidity and with increased rates of treatment non-responsiveness when comorbid with major depressive disorder and/or ADHD-CT.

METHODS: 200 clinically referred children with ADHD-CT, without comorbid major depressive disorder, were identified. "ODD", "ADHD-CT", "DD" and "anxiety disorders" symptoms were defined by composite measures of (1) semi-structured clinical interview and (2) parent and/or child standardized questionnaires. Standard multiple regression was used to examine how well "ADHD-CT", "DD" and "anxiety disorders" symptoms predict "ODD" symptoms.

RESULTS: Only "ADHD-CT" (15% of the variance) and "DD" (8% of the variance) symptoms made independent significant contributions to the prediction of "ODD" symptoms.

LIMITATIONS: The study's sample size did not allow "ODD" and "conduct disorder" symptoms to be analysed separately.

CONCLUSIONS: The association of DD with ODD may reflect a unique contribution of DD to ODD in children, whether ADHD-CT is present or not, or only when ADHD-CT is present.