Background: Relationships between illness severity and neurobiologic abnormalities in schizophrenia were studied in subpopulations varying in clinical severity.
Methods: Auditory ERPs were collected from 28 severely ill, chronically hospitalized schizophrenic men from a state hospital; 29 moderately ill inpatient and outpatient schizophrenic men from a veterans hospital; and 30 healthy male subjects from the community as controls. Clinical symptoms were evaluated in patients using the Brief Psychiatric Rating Scale (BPRS).
Results: Both schizophrenic patient groups had smaller P300 amplitude than the control subjects. Severely ill patients had smaller P300s than moderately ill patients and scored higher on three BPRS factor scores as well as BPRS Total. Among severely ill patients, P300 amplitude was unrelated to clinical symptoms. Among moderately ill patients, P300 was related to Withdrawal/Retardation, Anxiety/Depression, and BPRS Total. After combining patients, Thinking Disturbance emerged as an additional correlate of P300. Group differences in P300 could not be accounted for by group differences in symptom severity using analysis of covariance.
Conclusions: Reduced P300 amplitude marks the diagnosis of schizophrenia, but also reflects individual differences in severity, including positive symptoms. Previous failures to find relationships between positive symptoms and P300 may have been due to a restricted range of clinical severity.