Interictal dysphoric disorder: Further doubts about its epilepsy-specificity and its independency from common...

The interictal dysphoric disorder (IDD) is a proposed epilepsy-specific psychiatric condition characterized by a conglomerate of symptoms such as depression, irritability, euphoria, and anxiety. However, there are doubts about IDD as an independent entity and about its presumed epilepsy-specific nature.

Here, we investigated the association between psychiatric disorders and IDD in 120 patients with epilepsy, also analyzing potential associations between IDD symptoms and epilepsy-related variables. To test the epilepsy-specificity of IDD, we also studied IDD rates in 28 patients with pure psychogenic non-epileptic seizures. For the assessment of psychopathology, we used a structured clinical interview to determine the presence and nature of Axis I disorders and clinical questionnaires to assess psychopathological symptoms (anxiety, depression and severity of global distress). In accordance with most previous studies, we used the Interictal Dysphoric Disorder Inventory to assess IDD symptoms.

In our epilepsy group, we observed an IDD in 33% (42 of 120) of the patients. We diagnosed IDD in 39% (11 of 28) of the patients with psychogenic non-epileptic seizures without epilepsy. The majority of the patients with epilepsy with IDD have or had a psychiatric disorder (33 with a current, 6 with a past Axis I diagnosis). Patients with epilepsy with IDD had higher scores on all psychopathology questionnaires compared to the epilepsy patients without IDD.

Our findings suggest that IDD is not epilepsy-specific in nature, but occurs with the same frequency and the same pattern of symptoms in a purely psychiatric sample. We found a large overlap of IDD and common psychiatric comorbidities, mainly depression and anxiety disorders. This result calls the presumed nosological independency of IDD into question.