Previous psychiatric diagnoses preceding a first recorded schizophrenia diagnosis and subsequent clinical outcomes: a retrospective study using a Japanese claims database

Abstract Background Schizophrenia is a heterogeneous disorder in which affective symptoms commonly occur before the onset of frank psychosis. Depressive and anxiety symptoms preceding schizophrenia may complicate early diagnosis and influence subsequent clinical outcomes. This study aimed to describe psychiatric diagnostic patterns preceding first-recorded schizophrenia in Japan and examine clinical outcomes by the presence or absence of prior psychiatric diagnoses. Methods This retrospective cohort study used a nationwide Japanese health insurance claims database. Patients with a first recorded schizophrenia diagnosis between January 2006 and November 2023 and continuous insurance enrollment for ≥ 1 year before and after the index month (earliest recorded schizophrenia diagnosis) were included. Outcomes included time from the earliest psychiatric diagnosis (recorded using ICD-10 F-category codes) to schizophrenia diagnosis, psychiatric inpatient admission, and sick leave after the index month. Outcomes were compared between patients with and without prior psychiatric diagnoses using inverse probability weighting and Cox models. Results Among 21,590 eligible patients, 15,955 had ≥ 1 recorded psychiatric diagnosis before the index month and were evaluated for their earliest recorded psychiatric diagnosis. Of these patients, 5,788 were initially diagnosed with schizophrenia. In the other 10,167 patients, the most frequent diagnoses were depressive episodes (45.2%) and other anxiety disorders (21.6%). The mean ± standard deviation interval from the earliest recorded psychiatric diagnosis to the schizophrenia diagnosis was 12.8 ± 22.2 months overall and 20.2 ± 25.1 months among patients whose earliest recorded psychiatric diagnosis was not schizophrenia. The Cox regression model showed that patients with prior psychiatric diagnoses had a lower adjusted risk of psychiatric inpatient admission (HR, 0.87; 95% confidence interval [CI], 0.77–0.98; P = 0.020), although the Kaplan–Meier analysis and the patient-years analysis did not show significant differences between groups. The sick leave was higher at risk in patients with prior psychiatric diagnoses than those without by the Cox regression model (HR, 1.19; 95% CI, 1.11–1.27; P < 0.001), the Kaplan–Meier analysis (log-rank and Wilcoxon tests, both P < 0.001), and the patient-years analysis (the risk ratio 1.09 (95% CI, 1.04–1.15). Conclusions Depressive and anxiety disorders commonly occur before the first recorded schizophrenia diagnosis in Japan. Patients with prior recorded psychiatric diagnoses showed different patterns of subsequent psychiatric inpatient admission and physician-certified sick leave. Because the mean interval between the earliest recorded non-schizophrenia psychiatric diagnosis and the first recorded schizophrenia diagnosis was approximately 20 months, continued clinical assessment may be warranted. Trial registration Not registered.