Bridging Perspectives: Clinician–Adolescent Agreement on Psychopathological Severity in the European MILESTONE Cohort

Objectives: Adolescents transitioning from child and adolescent mental health services (CAMHS) to adult mental health services (AMHS) may face challenges in accurately identifying and reporting their mental health symptoms, often leading to discrepancies between clinician and patient evaluations. Using data from the MILESTONE project, this study aims to assess clinician-adolescent concordance over 24 months and identify domains of psychopathology with the highest disparities. Methods: Participants were assessed at baseline, 9, 15, and 24 months using the Health of the Nation Outcome Scales for Children and Adolescents (HoNOSCA) scale and were categorized in four diagnostic groups. Hierarchical cluster analysis identified symptom-based subgroups of patients based on clinician and patient-rated HoNOSCA scores. Concordance was evaluated through multilevel linear regression models, while Bland–Altman plots examined agreement between scores across time points. Results: Two clusters of patients were identified: one characterized by lower severity and greater prevalence, the other by higher complexity and fewer individuals. Clinician–patient concordance increased over time, rising from 77% to 83% by the second time point and stabilizing. Concordance varied across diagnostic categories, with anxiety showing the highest agreement and ADHD the lowest. Conclusions: Improved communication, psychoeducation, and tailored interventions may facilitate greater patient–clinician alignment, thereby supporting more favorable outcomes during this critical developmental period. Trial Registration: ISRCTN83240263; NCT03013595.