The Evolving Nosology of Schizophrenia: Relevance for Treatment

Abstract

The purpose of nosological systems (i.e., systems of classifying disease) is to define distinct disease entities which are uniquely identifiable and specifically treatable. Consequently, validity, reliability, and clinical utility are three critical elements of a useful diagnostic system. Our system of psychiatric classification recently underwent a major revision, resulting in the publication of the Diagnostic and Statistical Manual of Mental Disorders (DSM)-5 in 2013. Whereas improving validity and reliability of psychiatric diagnoses were key objectives in its development, enhancing clinical utility was the primary goal. With reference to psychotic disorders, changes in the new manual addressed limitations in DSM-IV while incorporating new information about the nature of these disorders generated over the past 20 years. With regard to schizophrenia, variation in distinct psychopathological dimensions is better able to account for the heterogeneity of this disorder than traditional subtypes. Therefore, changes in DSM-5 included elimination of the classic subtypes of schizophrenia and the addition of unique psychopathological dimensions. In view of the poor reliability and limited validity of schizoaffective disorder as defined in DSM-IV a clearer definition was provided in DSM-5. Additionally, the discrepant treatment of catatonia in DSM-IV has been corrected and it is now listed consistently across the DSM-5 manual. A new category of Attenuated Psychosis Syndrome is included in Section 3 as a condition for further study. In this chapter, the revisions in the DSM-5 criteria for schizophrenia spectrum and other psychotic disorders are summarized and their implications for clinical practice discussed.