Psychosis in a population cohort: A four class four dimension model of schizophrenia and affective psychoses

• Main Author: Murray, Valerie
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2005
• Subjects: Bipolar disorder; Clinical psychology; Epidemiology; Mental disorders; Womens health
• ISBN: 1369579535; 9781369579536

Psychosis is a low prevalence disorder with high cost to those affected, their families, and society in general. Enormous effort to determine the causes and pathophysiology of schizophrenia has been relatively unrewarded, and no robust biological markers have been identified. It is argued that reliance on the Kraepelinian dichotomy model of psychosis, as demonstrated in ICD-10 and DSM- IV, impedes research, especially in psychiatric genetics. Modelling the psychoses from first principles demands a population based a theoretical approach. By considering the whole spectrum of psychosis in a general population the natural boundaries of the underlying disorder(s) may be best understood. This thesis describes the use of both dimensional and categorical approaches in the same data, providing complementary approaches to delineating the psychosis phenotype. Classes and dimensions thus identified are validated by their pattern of associations with many variables previously known to be important in schizophrenia. The findings are anchored in the literature by making comparisons with traditional diagnostic categories and first rank symptoms in addition to comparison with other studies. For genetic studies, four classes which are well demarcated are a useful alternative to DSM-III-R diagnoses, comprehensively encompassing the entire range of psychosis. Likewise the four dimensions should prove useful in quantitative trait loci approaches in genetic studies, and provide a dimensional scale which could be of clinical value. While it is not suggested that the four latent classes should replace current diagnoses, their validation challenges the continued acceptance of the current plethora of diagnostic categories. The Kraepelinian dichotomy appears to be supported by the clear distinction between the disorganisation and bipolar classes, but the other classes are less distinctively different. It is timely to consider reclassifying the psychoses from first principles, based on a series of larger population based empirical studies. The current concept of schizophrenia is probably too heterogeneous. The latent classes point to the utility of dementia praecox (disorganisation class) as being of a different substance, representing the only truly non-affective psychosis. Until the terminology is changed, the assumptions inherent in the term schizophrenia will persist and continue to restrict the recognition of the true underlying subtypes in psychosis. Factor analysis and latent class analysis are useful in attempting to reveal the latent variables in psychosis which might better represent underlying diseases compared to traditional diagnoses. While it is hoped that the four latent classes may truly be "dividing nature at its joints" this can only be proven if and when biological markers are found which are differentially distributed across these four classes.