Intellectual disability and psychotic disorders of adult epilepsy

Purpose: To investigate the prevalence, psychopathology, and cognitive functions associated with psychotic disorders among adult epilepsy patients with intellectual disability (ID) based on a multicenter study in Japan. Methods: The study was divided into three phases; a prevalence study of psychotic disorders among new referrals of epilepsy, a polydiagnostic comparative study of patients with psychotic epilepsy and those with schizophrenia, and a neuropsychological study of patients with psychotic epilepsy and education level- matched controls. Results: Among 336 new referrals of epilepsy, a higher prevalence of psychotic disorders was found among patients with ID (24%) than among those with normal intelligence (6%). The psychotic symptoms and operational diagnoses of psychotic epilepsy patients with ID were similar to those of patients with normal intelligence. A wide range (7- 86%) of psychotic epilepsy patients was diagnosed as having schizophrenia, depending on the operational criteria used. Patients with psychotic epilepsy had more disturbances in verbal memory and attention functions than did the controls. Conclusions: Epilepsy patients with ID show a predisposition to develop psychotic disorders. Distinguishing their psychotic symptoms from those of schizophrenia is difficult. Subtle cognitive disturbances predispose to psychotic disorders in epilepsy.