Does operational diagnosis of schizophrenia significantly impact intellectual deficits in psychotic disorders?

Abstract

Background: Evidence suggests that, as a group, patients with schizophrenia have intellectual deficits that may precede the manifestation of psychotic symptoms; however, how successfully intelligence tests are able to discriminate schizophrenia from other psychotic disorders has yet to be investigated in detail. Methods: Using Wechsler Adult Intelligence Scale-Revised (WAIS-R) data for 55 inpatients with schizophrenia and 28 inpatients with non-schizophrenic psychotic disorders (NSPD) (schizophreniform disorder, brief psychotic disorder, delusional disorder, psychotic disorder due to a general medical condition, and psychotic disorders not otherwise specified), intelligence performance was compared between schizophrenia and NSPD and among different subtypes of schizophrenia. Results: There were no significant differences in intelligence quotient (IQ), verbal IQ (VIQ) and performance IQ (PIQ) discrepancy, and subtest scores of WAIS-R between the patients with schizophrenia and those with NSPD. These diagnostic groups were not discriminated well by any WAIS-R variables. Schizophrenia patients with prominent negative symptoms, on the other hand, had a significantly larger IQ discrepancy (VIQ > PIQ) than those without prominent negative symptoms and NSPD patients. Intelligence performance in schizophrenia did not differ with respect to diagnostic subtypes and longitudinal courses. Conclusions: The current study failed to show diagnostic usefulness of WAIS-R in discriminating schizophrenia and other psychoses. A diagnosis of schizophrenia does not significantly impact intellectual deficits in psychotic disorders. © 2007 The Authors. Journal Compilation © 2007 Blackwell Publishing Ltd.