Psychoses and epilepsy: are interictal and postictal psychoses distinct clinical entities?

To evaluate further the relevance of designating psychotic episodes as either postictal or interictal, we compared several biologic variables between epilepsy patients with and without psychosis.

The study subjects comprised 282 patients with psychosis (36 with postictal psychosis, 224 with interictal psychosis, and 22 with both postictal and interictal psychoses, i.e., bimodal psychosis), and 658 epilepsy patients without psychosis. The clinical characteristics of these patients were reviewed retrospectively by experienced neuropsychiatrists. Factors predicting the development of each type of psychosis were determined by serial multivariate logistic regression analyses.

Factors that were comparable between postictal and interictal psychoses were intellectual function, family history of psychosis, epilepsy type, and the presence of complex partial seizures. In contrast, age at the onset of epilepsy and at the onset of psychosis and the presence of generalized tonic-clonic seizures differed for the three types of psychosis. Patients with bimodal psychosis showed characteristics associated with both postictal and interictal psychoses.

This study documented conditions, including both general factors and epilepsy-related factors, common to epilepsy patients with psychosis, regardless of chronologic distinctions. Certain epileptic processes appear to have equal influence on postictal and interictal psychoses. However, some differences between postictal and interictal psychoses suggest that these chronologic descriptors are valid. Our findings confirmed that psychosis associated with epilepsy should not be defined as a single, simple condition but rather as a complex condition with several possible subcategories.