Empirical support for DSM-IV schizoaffective disorder: clinical and cognitive validators from a large patient sample

The diagnosis of schizoaffective disorder has long maintained an uncertain status in psychiatric nosology. Studies comparing clinical and biological features of patients with schizoaffective disorder to patients with related disorders [e.g., schizophrenia and bipolar disorder] can provide an evidence base for judging the validity of the diagnostic category. However, because most prior studies of schizoaffective disorder have only evaluated differences between groups at a static timepoint, it is unclear how these disorders may be related when the entire illness course is taken into consideration.

We ascertained a large cohort [N = 993] of psychiatric patients with a range of psychotic diagnoses including schizophrenia with no history of major affective episodes [SZ-; N = 371], schizophrenia with a superimposed mood syndrome [SZ+; N = 224], schizoaffective disorder [SAD; N = 129] and bipolar I disorder with psychotic features [BPD+; N = 269]. Using cross-sectional data we designed key clinical and neurocognitive dependent measures that allowed us to test longitudinal hypotheses about the differences between these diagnostic entities.

Large differences between diagnostic groups on several demographic and clinical variables were observed. Most notably, groups differed on a putative measure of cognitive decline. Specifically, the SAD group demonstrated significantly greater post-onset cognitive decline compared to the BP+ group, with the SZ- and SZ+ group both exhibiting levels of decline intermediate to BPD+ and SAD.

These results suggest that schizoaffective disorder may possess distinct features. Contrary to earlier formulations, schizoaffective disorder may be a more severe form of illness.