Reshaping the diagnostic borders: Historical analysis of the diagnostic changes following the introduction of the schizophrenia concept

Background: Although the concept of schizophrenia is still widely presented as having replaced that of dementia praecox, studies have shown that the former was broader than the latter, resulting in a more complex diagnostic redistribution. However, this is poorly documented by quantitative approaches. Aims: We sought to test the hypothesis that the use of the concept of schizophrenia had caused a diagnostic redistribution and to quantify it. Method: A retrospective study, based on admission register archives of the Strasbourg University Clinic of Psychiatry was conducted. The frequency of diagnoses given to patients were examined at two key time periods: one before (TP1) and one after (TP2) the introduction of the schizophrenia concept (established between 1926 and 1928). Eight main diagnoses related to schizophrenia were considered. Results: Patients diagnosed with schizophrenia at TP2 mainly received the diagnoses of dementia praecox but also depression, hebephrenia, manic depressive illness, hysteria, paraphrenia, catatonia and mania at TP1. Dementia praecox and hebephrenia were the most relayed by schizophrenia. Bayesian sensitivity analyses confirmed the robustness of our data against distinct scenarios challenging our hypothesis. Conclusions: Our results confirm the broadening of the concept of schizophrenia compared to that of dementia praecox but also qualify the different concepts supposed to have been impacted. They provide unique quantitative data that define the contours of the diagnostic redistribution thus provoked. They also give relevant input in the current context where the need to rethink the DSM/ICD concept of schizophrenia is still debated.