Neuropsychological function and dysfunction in schizophrenia and psychotic affective disorders

Abstract

Background: Mounting evidence suggests that compromised neurocognitive function is a central feature of schizophrenia. There are, however, schizophrenia patients with a normal neuropsychological (NP) performance, but estimates of the proportion of NP normal patients vary considerably between studies. Neurocognitive dysfunction is also a characteristic of other psychotic disorders, yet there are inconsistencies in the literature regarding the similarity to impairments in schizophrenia. NP normality in psychotic affective disorders has not been systematically studied.

Methods: Data came from the Suffolk County Mental Health Project, an epidemiological study of first-admission patients with psychotic disorders. Respondents with a diagnosis of schizophrenia (N = 94) or schizoaffective disorder (N = 15), bipolar disorder (N = 78), and major depressive disorder (N = 48) were administered a battery of NP tests assessing 8 cognitive domains 2 years after index admission. Patients' performance profile was compared, and their NP status was classified based on 3 previously published criteria that vary in their stringency.

Results: The 4 diagnostic groups had comparable NP performance profile patterns. All groups demonstrated impairments in memory, executive functions, and attention and processing speed. However, schizophrenia patients were more impaired than the other groups on all cognitive domains. Results were not attenuated when IQ was controlled. Prevalence of NP normality ranged between 16% and 45% in schizophrenia, 20% and 33% in schizoaffective disorder, 42% and 64% in bipolar disorder, and 42% and 77% in depression, depending on the criterion employed.

Conclusions: Evidence suggests that differences in NP performance between schizophrenia and psychotic affective disorders are largely quantitative. NP impairment is also common in psychotic affective disorders. A significant minority of schizophrenia patients are NP normal.

Fig. 1.

Neuropsychological performance profile of schizophrenia, schizoaffective, psychotic major depressive disorder, and psychotic bipolar disorder patients (average normal performance indicated by gray line) (raw data is available from the corresponding author).

Fig. 2.

Rates of neuropsychological impairment as a function of applied criteria in schizophrenia, schizoaffective, psychotic major depressive disorder, and psychotic bipolar patients. GDS, Global Deficit Score dichotomized as lower than or greater and equal to 0.5; CSCI 1SD, Clinically Significant Cognitive Impairment with cut-off corresponding to 1SD below norms on at least 2 ability areas; IPR, Individual Profile Rating, dichotomized to severe or abnormal versus borderline normal or normal.