Interictal psychoses in comparison with schizophrenia--a prospective study

To prospectively investigate the incidence of interictal psychoses of epilepsy patients, and make a comparison between those with interictal psychoses and patients with schizophrenia in respect to their responses to antipsychotic drugs, as well as psychotic states.

We undertook a two-part prospective investigation. In Part I, the psychotic episodes of 619 epilepsy patients were investigated, while 182 patients with psychotic syndromes were followed in Part II, of whom 59 were diagnosed with schizophrenia and 13 with epilepsy with interictal psychoses. The Positive and Negative Syndrome Scale was used for efficacy assessment.

The average annual incidence of interictal psychosis was 0.42% during the 56-month study period. A significant difference was found between patients with schizophrenia and epilepsy patients with interictal psychoses in respect to results on the negative subscale of the PANSS at the initial examination (mean scores of 18.1 and 13.2, respectively, p = 0.004). The response rates one year later for these groups were 27.1% and 53.8%, respectively, which showed a trend of better response to the antipsychotic medication by the epilepsy group (p = 0.098). Initial and maximum doses of antipsychotic drugs used for epilepsy patients with interictal psychoses were significantly lower than those used for patients with schizophrenia (p = 0.008 and p = 0.006, respectively).

Schizophrenia and epileptic psychosis showed different symptom profiles. On average, epilepsy patients with interictal psychoses achieved higher remission rates with lower doses of antipsychotic drugs as compared to patients with schizophrenia in the present 1-year follow-up study.