Premorbid performance IQ deficit in schizophrenia

Objective: Performance IQ (PIQ) is often lower than verbal IQ (VIQ) in schizophrenic patients. Whether PIQ < VIQ precedes psychotic symptoms in schizophrenia remains uncertain. Method: We investigated premorbid IQ scores in 63 subjects assessed at a child and adolescent psychiatric unit (mean age 13.1 years, SD 3.2), who at follow-up in adulthood (mean age 30.9 years, SD 3.9) received a lifetime RDC diagnosis of schizophrenia-related psychosis, affective disorder, or no psychiatric disorder. Results: Premorbid PIQ < VIQ significantly differentiated the groups with schizophrenia-related psychosis and no psychiatric disorder. Subjects with schizophrenia-related psychosis had a significantly lower mean value for premorbid PIQ, but not VIQ, compared to subjects who developed affective disorder or subjects without psychiatric disorder. Conclusion: Our results emphasize premorbid intellectual deficits in schizophrenia. Those deficits might largely be in consequence of an impairment on the PIQ scale.