Quantitative psychopathology of interictal psychosis in epilepsy; interaction between epilepsy-related and...

There is a historical debate whether psychopathology of epilepsy psychosis is unique to epilepsy or common to other psychoses. However, a large comprehensive studies on this issue are scarce. To clarify the characteristics of interictal psychosis (IIP), we evaluated psychopathology quantitatively.

This study included 150 patients with IIP (epilepsy+/psychosis+), 187 patients with schizophrenia (SC: epilepsy-/psychosis+), 182 patients with epilepsy (EP: epilepsy+/psychosis-), and 172 non-clinical individuals (NC: epilepsy-/psychosis-). The IIP group comprised 127 chronic and 23 brief psychoses. Age, sex, and years of education, onset and duration of psychosis, and onset and duration of epilepsy were matched among the groups. The psychopathology was evaluated using the 16-item Brief Psychiatric Rating Scale (BPRS), which comprises three symptom factors namely negative symptoms (NS), positive symptoms (PS), and anxiety-depressive symptoms (ADS).

For overall 16-BPRS and NS factor scores, there were significant interactions between epilepsy-related (epilepsy+/-) and psychosis-general (psychosis+/-) effects. The EP exhibited higher scores than did the NC, whereas the IIP exhibited lower scores than did the SC. For PS and ADS factor scores, the IIP and SC exhibited a significant psychosis-general effect. Chronic IIP was associated with more serious psychopathologies than was brief IIP. However, limited with chronic IIP, there was a significant interaction between epilepsy-related and psychosis-general effects on the overall 16-BPRS and NS factor scores.

These findings demonstrate the first large quantitative evidence on the unique psychopathology of IIP which has been only narratively described. The psychopathology is associated with the interaction between epilepsy-related and psychosis-general effects.