Recent trends in hospital admission due to bipolar disorder in 10-19-year-olds in Spain: A nationwide population-based study.

Introduction: Bipolar disorder (BD) hospitalization rates in children and adolescents vary greatly across place and over time. There are no population-based studies on youth BD hospitalizations in Spain.
Methods: We identified all patients aged 10-19 hospitalized due to BD in Spain between 2000 and 2021, examined their demographic and clinical characteristics, and assessed temporal trends in hospitalizations - overall and stratified by age and presence of additional psychiatric comorbidity. We used Joinpoint regressions to identify inflection points and quantify whole-period and annual percentage changes (APCs) in trends.
Results: Of 4770 BD hospitalizations in 10-19-year-olds between 2000 and 2021 (average annual rate: 4.8 per 100,000), over half indicated an additional psychiatric comorbidity, most frequently substance abuse (62.2%), mostly due to cannabis (72.4%). During the study period, admissions increased twofold with an inflection point: Rates increased annually only between 2000 and 2008, for APCs 34.0% (95% confidence interval: 20.0%, 71.1%) among 10-14-year-olds, 10.3% (6.4%, 14.3%) among 15-19-year-olds, and 15.5% (11.5%, 22.7%) among patients with additional psychiatric comorbidity. Between 2009 and 2021, rates decreased moderately among 10-14-year-olds - APC: -8.3% (-14.1%, -4.4%) and slightly among 15-19-year-olds without additional psychiatric comorbidity - APC: -2.6(-5.7, -1.0), remaining largely stable among 15-19-year-olds overall.
Conclusions: Recent trends in hospitalization due to BD in 10-19-year-olds in Spain indicate salient increases in the early 2000s - especially among (i) patients aged 10-14 (decreasing moderately after 2009 among 10-14-year-olds and plateauing among 15-19-year-olds) and (ii) patients with additional psychiatric comorbidity (i.e., cannabis use disorder). These findings suggest links with recent changes in clinical practices for children and recent trends in substance use among Spanish youth.
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