Density of striatal D2 receptors in untreated first-episode psychosis: an I123-IBZM SPECT study.

There is as yet no definite prognostic marker to determine whether a first-episode psychosis will become schizophrenia or not. The aim of the present study is to address whether the mechanism of sensitization of the subcortical dopaminergic pathway - yielding to an increase of the postsynaptic D2 receptors - may serve as a prognostic marker of clinical outcome in drug naïve patients with a first-episode psychosis, by means of a prospective and multicentric study with untreated first-episode psychosis patients (n=37). 123I-IBZM SPECT was performed at the time of the inclusion in the study, before antipsychotic medication was initiated. One year later, patients were assessed again so as to determine their diagnosis. There was a significant group effect at baseline in D2 Striatal/Frontal (S/F) ratios (F=10.2, p<0.001). Bonferroni posthoc comparisons attested significant differences between diagnosis (p=0.006), and between schizophrenia and control groups (p<0.001) but no differences between non-schizophrenia and control groups (p=0.9). The logistic regression model showed that D2R binding (p=0.02) and PAS (Premorbid Adjustment Scale) adulthood score (p=0.03) were predictive of the final diagnosis (schizophrenia/non-schizophrenia; Nagelkerke R(2)=0.59; X(2)=11.08, p=0.001). These findings replicate previous results on the usefulness of D2R binding as an objective prognostic parameter, together with the evaluation of premorbid adjustment, of the evolution of first-episode psychosis. In this regard, the results may provide a new view in the approach of early and personalized treatment in the debut of a psychosis.