Interictal dysphoric disorder of epilepsy: A continuing diagnostic challenge

The interictal dysphoric disorder (IDD) is a proposed epilepsy-specific mood disorder characterized by a cluster of symptoms such as depressed mood, irritability, euphoria, and anxiety. Since its introduction, the concept of IDD has been a matter of debate. This study aimed to evaluate the frequency of the IDD and the association between psychiatric disorders and IDD. We also analyzed potential associations between IDD symptoms and epilepsy-related variables.

A consecutive group of 118 outpatients with epilepsy were screened. Ninety-six patients met inclusion criteria and examined by a trained psychiatrist using Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders fourth edition Text Revision (DSM-IV-TR) (SCID-I). In order to diagnose IDD, all participants completed the self-rating questionnaire consisting of a set of questions aimed to assess the eight key symptoms of IDD. On completion of the questionnaire, the psychiatrist reviewed all the data for completeness and accuracy with the patient.

In our group with epilepsy, we observed IDD in 49.0% (47 of 96) of people with epilepsy (PWE) with substantial overlap (85%) of IDD with depressive and anxiety disorders. The frequency of depressive mood, anergia, and irritability was significantly higher in patients with IDD diagnosis. Older age at epilepsy onset was associated with IDD.

The cross-sectional study design, a consecutive sample of patients presenting to a tertiary referral center, a small sample size of the population, and applied methodology could have affected the results.

The present study indicates that IDD occurs in high frequency in PWE with a substantial overlap of IDD with depressive and anxiety disorders. The study highlights the importance of the observer-based systematic approach for diagnosing IDD and the usage of operationalized diagnostic criteria for psychiatric comorbidities in PWE. Future research should be directed at validating whether IDD is nosologically independent of other psychiatric conditions.