Temporal changes in the incidence of treated psychiatric and neurodevelopmental disorders during adolescence: an analysis of two national Finnish birth cohorts.

Background: Comprehensive overviews of the temporal changes in treated psychiatric and neurodevelopmental disorders during adolescence are scarce. We reviewed data from two national cohorts, 10 years apart, to establish the change in use of specialised services for psychiatric and neurodevelopmental diagnoses in Finland.

Methods: We compared the nationwide register-based incidence of psychiatric and neurodevelopmental diagnoses between the 12th birthday and 18th birthday of adolescents born in Finland in 1987 and 1997. Adolescents who emigrated or died before their 12th birthday and those with missing covariate data were excluded, as were those who, when aged 11 years, had lived in a municipality belonging to a hospital district with obviously incomplete data reports during any follow-up years in our study. Our primary outcomes were time to incident specialised service use for any psychiatric or neurodevelopmental disorder and for 17 specific diagnostic classes. We also investigated whether adolescents who died by suicide had accessed specialised services before their deaths.

Findings: The cumulative incidence of psychiatric or neurodevelopmental disorders increased from 9·8 in the 1987 cohort to 14·9 in the 1997 cohort (difference 5·2 percentage points [95% CI 4·8-5·5]) among girls, and from 6·2 in the 1987 cohort to 8·8 in the 1997 (2·6 percentage points [2·4-2·9]) among boys. The hazard ratio for the overall relative increase in neurodevelopment and psychiatric disorders in the 1997 cohort compared with the 1987 cohort was 1·6 (95% CI 1·5-1·8) among girls and 1·5 (1·4-1·6) among boys. Of the studied diagnostic classes, we noted significant (ie, p<0·001) relative increases for ten of 17 diagnoses among girls and 11 among boys. Of the adolescents who died by suicide before age 18, only five of 16 in the 1987 cohort and two of 12 in the 1997 cohort had used specialised services in the 6 months before their death.

Interpretation: The large absolute rise in service use for psychiatric or neurodevelopmental disorders points to the need to deliver effective treatment to a rapidly increased patient population, whereas the relative increase in specific diagnoses should inform clinical practice. Despite increasing service use, identification of adolescents at risk of suicide remains a major public health priority.

Funding: Academy of Finland, Brain and Behavior Research Foundation, Finnish Medical Foundation.