Diagnosis and Classification of the Schizophrenia Spectrum Disorders

Abstract

The classification of schizophrenia related disorders have been evolving with advances in psychiatric research. In 1893 Emil Kraepelin distinguished dementia praecox from manic-depression, heralding the diagnosis of schizophrenia as a separate entity, but this distinction has since been challenged by data from genetic epidemiology. Over the past century, two major classification systems emerged: the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM) and the World Health Organization’s International Statistical Classification of Diseases and Related Health Problems (ICD), of which new editions are expected to be soon published. The latter criteria are typically used in European countries, while the DSM criteria are used in the United States and the rest of the world, as well as prevailing in research studies. As with other psychiatric disorders, some have suggested that the diagnosis of psychotic disorders would be better addressed as individual dimensions of psychotic experiences (e.g. hallucinations and delusions) along which everyone varies, such that there is a spectrum or continuum rather than a cut-off between disorders and normality. Some disorders in the schizophrenia spectrum, such as schizoaffective disorder and schizotypal personality disorder have also been criticized for a relatively low interrater reliability, in part due to the difficulty of establishing fine grained timecourse information and to identifying subtle, sub-threshold psychotic type phenomena. This chapter discusses past and present diagnostic classifications of schizophrenia spectrum disorders, and research considerations for further improving our nosological system.