The incidence of disruptive behaviour disorders and comorbid ADHD diagnoses: a register‑based study of perinatal and psychosocial factors

Background Disruptive behaviour disorders (DBDs) frequently occur alongside attention deficit hyperactivity disorder (ADHD); however, the current incidence and extent of this overlap remain unclear. We aimed to estimate the cumulative incidence of DBD diagnoses and their comorbidity with ADHD and the trends in the incidences over time. Methods We used register data of live-born children from 2001–2005 (N = 282,773). The cumulative incidence of DBD diagnoses up to age 12 was studied. DBDs were defined by conduct disorder (CD, F91.x) and mixed disorders of conduct and emotions (F92.x), based on the 10th International Classification of Diseases. Concomitant ADHD (F90.x, F98.8) diagnoses were examined, and analyses were adjusted for perinatal and psychosocial factors. Results The cumulative incidence of CD and mixed disorder of conduct and emotions diagnoses were 0.8% (2,208) and 1.5% (4,128) respectively in 269,490 study children followed up to 12 years. The cumulative incidence of DBDs varied by cohort and was higher in later-born cohorts. In boys, incidence increased from 2.8% in the 2001 cohort to 3.3% in the 2005 cohort, and in girls from 0.8% to 1.1% (p < 0.0001 and p = 0.0007, respectively). Among 5,573 children with a DBD diagnosis (763 with both F91.x and F92.x diagnoses), 40.6% (n = 2,260) had comorbid ADHD. The DBD–ADHD comorbidity was more likely (adjusted odds ratio [95% Confidence Intervals]) among children whose mothers smoked during pregnancy (2.6 [2.4–2.9]), were single (1.8 [1.6–2.1]), were unemployed (1.2 [1.1–1.3]) or had a psychiatric disorder between pregnancy and the child’s first four years (2.5 [2.2–2.8]), as well as among boys (6.8 [6.0–7.8]). Over the cohorts, ADHD diagnosis increased in boys with DBDs diagnosis (p<0.05), but not in girls (p>0.05). Conclusions The cumulative incidence of diagnosed DBDs has varied over the years and is increasing modestly. The comorbidity with ADHD is common and increasing in boys, and higher odds for comorbidity associates with male sex and maternal psychosocial adversities.