Introduction: The poor premorbid IQ has been considered as a predisposing factor for the development of schizophrenia and other psychoses as well as predictive of poor long-term outcome. We hypothesise that premorbid IQ could influence symptom expression during an index episode (i.e. a short-term outcome).
Aim of the study: We studied 48 patients with schizophrenic disorder and 56 with bipolar disorder during an 'index episode' using the test di intelligenza breve (TIB) for the premorbid IQ evaluation, and the positive and negative syndrome scale (PANSS).
Results: Using the premorbid IQ as a criterion variable (i.e. low versus high IQ groups) the one-way ANOVA analysis showed that low IQ schizophrenic patients had more PANSS positive symptoms and "thought disturbances" than both high and low IQ bipolars. The low IQ schizophrenic patients showed more cognitive symptoms than bipolar patients with high IQ. Furthermore, no PANSS differences were seen between high IQ schizophrenics and low IQ bipolars. In the total and bipolar groups the correlation coefficients between TIB scores and PANSS scales reached statistical significance for the cognitive cluster only. No correlations were seen in the schizophrenic group.
Conclusion: This categorisation (i.e. low versus high IQ) adds clinically relevant knowledge to patients who, in spite of having similar symptom profile (i.e. high IQ schizophrenic patients and low IQ bipolar patients), fall into different diagnostic categories.