Schizophrenia and Schizoaffective Disorder: One Condition or Two?

There is long-standing debate regarding whether or not schizophrenia and schizoaffective disorder represent a single condition or two distinct disorders. Despite diagnostic criteria that differentiates these illnesses, clinical practice relies heavily upon subjective methods to separate these symptomatically overlapping conditions. Cognitive functioning has represented one of the main parameters evaluated in an attempt to discriminate between schizophrenia and schizoaffective disorder unfortunately with contradictory results. Further, these comparative studies have traditionally been limited to intellectual and cognitive functioning and have not captured other factors such as social cognition. The current research tested the hypothesis that these two conditions are cognitively distinguishable based on comprehensive and well-validated measures of neurocognition (processing speed, working memory, visual learning and memory, verbal learning and memory, reasoning and problem solving, and attention). This study is also the first to compare these diagnostic groups on multiple measures of social cognition (emotion perception, theory of mind, and attribution bias). Research participants included outpatients with a diagnosis of schizophrenia (n = 70) and schizoaffective disorder (n = 46), as well as comparison participants (n = 146). Across the various neurocognitive domains, there were no significant differences between diagnostic groups, with both uniformly performing worse than the comparison group. Discriminant function analysis revealed that performance on cognitive measures classified comparison group participants with a high degree of accuracy (93.8%) but far less so for those with schizophrenia (51.7%) and schizoaffective disorder (7.7%), suggesting substantial overlap between diagnostic groups on cognitive functioning. In terms of social cognition, the schizophrenia group was impaired on emotion perception relative to the schizoaffective disorder and comparison groups. The schizophrenia group was also impaired on theory of mind relative to the comparison group. Discriminant function analysis showed that performance on social cognitive tasks classified comparison participants accurately (83.4%) but far less so for those with schizophrenia (55.8%) or schizoaffective disorder (3.3%). These findings indicate that these two disorders are cognitively homogeneous, which is congruent with the majority of the literature, and suggests that schizoaffective disorder is not a distinct entity but is a subtype of schizophrenia. Implications for research and clinical practice are discussed.