Importance: Individuals with mental disorders often experience multiple disease episodes and diagnostic changes after initial psychiatric contact. However, studies that comprehensively investigate heterogeneity in disease development beyond pairs of comorbid diseases and mortality from a transdiagnostic perspective have been lacking. Objective: To comprehensively study sex and age patterns of disease development for 7 major groups of mental disorders. Design, Setting, and Participants: This cohort study included data from linkage of national Danish registers of all adult individuals living in Denmark between 2000 and 2018. Adult individuals with 1 of the following first-time mental disorder diagnoses were included: substance use disorder, schizophrenia, psychotic disorder other than schizophrenia, mania and bipolar disorder, major depressive disorder, anxiety-related disorders, or personality disorders. Data were analyzed from August 2023 to December 2025. Main Outcome and Measures: For each of the 7 mental disorder categories, age- and sex-specific estimates of (1) the number of diagnostic shifts, (2) the absolute risk of pairwise diagnostic shifts, (3) the absolute risk of diagnostic recurrence, and (4) the number of psychiatric contacts encompassing inpatient admissions, outpatient treatment courses, and emergency department visits were calculated using age groups 18 to 24 years, 25 to 39 years, 40 to 59 years, and 60 years or older and male and female sex. Results: A total of 273 400 individuals (mean SD age at first contact, 41.4 18.7 years; 150 349 female 55.0%) with mental disorders were included and followed up for 2.1 million person-years. Diagnostic shifts were observed among 66 474 individuals (24.3%), and 30 558 (11.8%) had multiple diagnostic shifts. Individuals with psychotic disorders had the highest number of psychiatric contacts and diagnostic shifts. Younger age at first contact was associated with more psychiatric contacts and higher number of diagnostic shifts irrespective of diagnosis given at first contact as well as higher probabilities for most pairwise diagnostic shifts and diagnostic recurrence. Males showed a pattern of higher absolute risk of diagnostic shifts to substance use disorders and schizophrenia spectrum disorders than females, whereas females had a higher probability of diagnostic shifts to mood disorders, anxiety-related disorders, and personality disorders. Conclusions and Relevance: This study found that disease development across the 4 outcomes was highly dependent on the specific diagnosis given at first contact as well as the patient's sex and age group. These findings are important for treatment planning and follow-up strategies to ensure that preventive initiatives are offered to high-risk individuals.
Wandall et al. (Wed,) studied this question.