A multicenter study on the prevalence of psychiatric disorders among new referrals for epilepsy in Japan.

PURPOSE:To investigate the prevalence rate and risk factors of psychiatric disorders among new referrals for epilepsy, a multicenter study was conducted by using the International League Against Epilepsy (ILAE) criteria for epilepsy and the ICD-10 criteria for psychiatric disorders. METHODS:From April 2000 to March 2001, 398 patients with epilepsy, who were referred to nine neuropsychiatric outpatient clinics specialized for epilepsy in the Tokyo metropolitan area, were evaluated by using a newly developed five-axis classification scheme. RESULTS:Forty-two percent of the subjects showed a psychiatric disorder. Twenty-four percent of the total showed psychiatric disorders, including neurotic disorders in 8%, psychotic disorders in 7%, and affective disorders in 1%. In addition, 23% of the total showed mental retardation, and 18% showed personality disorders. A logistic regression analysis revealed that the three risk factors for a psychiatric disorder were mental retardation, temporal lobe epilepsy (as opposed to other subtypes), and a high seizure frequency. CONCLUSIONS:The presence of mental retardation was the primary risk factor for developing a psychiatric disorder, especially a schizophrenia-spectrum disorder. The type of epilepsy alone is not a strong predictor of psychiatric illness, and intractable temporal lobe epilepsy with a high seizure frequency is accountable for the link between the epilepsy and the psychiatric illness.