Characterization of different subtypes of schizophrenia: Premorbid functioning, neurophysiological differences, functional outcomes

Abstract

Introduction Although not included in current diagnostic systems, deficit versus non-deficit and resistant versus non-resistant schizophrenia subtypes look more promising than traditional schizophrenia subtypes in terms of stability across time, clinical utility and interest for research. Aims To critically analyze evidence supporting the validity of two schizophrenia subtypes: Deficit Schizophrenia (DS) and Treatment Resistant Schizophrenia (TRS). Methods Empirical data supporting the validity of DS and TRS subtypes will be critically reviewed. Results DS, in comparison with non-deficit schizophrenia, is characterized by poorer premorbid functioning, more insidious onset, lower prevalence of dysphoria, hostility, suicidal ideation, depressive symptoms and substance abuse, different neurobiological abnormalities, and poorer response to treatment. The diagnosis of DS shows high reliability and stability across time. However, research based on this approach has proven difficult, especially in first-episode schizophrenia, and findings have not been as homogeneous as expected. TRS patients, as compared to non-TRS ones, show persisting psychotic symptoms, greater severity of negative symptoms, more severe cognitive dysfunctions, poorer premorbid functioning, longer duration of untreated psychosis, more frequent co-morbidity with personality disorders, earlier illness onset and poorer social functioning. Conclusions Future research should consider a) refining diagnostic criteria for DS and identifying valid DS endophenotypes; b) dissecting TRS based on psychopathological characteristics (e.g. presence of primary and persistent negative symptoms or persistently severe positive symptoms), and underlying neurobiological mechanisms (e.g. dopamine synthesis capacity and glutamatergic transmission).