Purpose: Different authors suggested the occurrence of a pleomorphic affective syndrome in patients with epilepsy named interictal dysphoric disorder (IDD). We sought to investigate whether IDD occurs only in patients with epilepsy and to validate IDD features against DSM-IV criteria.
Methods: Consecutive patients with a diagnosis of epilepsy (E) or migraine (M) have been assessed using the BDI, MDQ, and the Interictal Dysphoric Disorder Inventory (IDDI), a questionnaire specifically created to evaluate IDD symptoms. Diagnosis of current and lifetime DSM-IV Axis I disorders was established using the MINI Plus version 5.0.0.
Results: A total of 229 patients (E = 117; M = 112) were evaluated. Females were significantly more represented in the migraine group (E = 46.5% vs. M = 73.3% p = 0.009), but there was no difference in age, duration of the disease, or education level. Patients with epilepsy were more likely to screen positively at MDQ (E = 17% vs. M = 5.3% p = 0.006) and to have a diagnosis of bipolar disorder (E = 14.5% vs. M = 4.5% p = 0.013) as compared to migraine patients. There was no between-groups difference in IDD prevalence (E = 17%; M = 18.7%) and IDDI total scores (E = 4.1 ± 2.0 vs. M = 3.8 ± 2.0). Validation of IDD against DSM-IV categories showed current major depression being the foremost diagnostic category correlated with IDD in both epilepsy (OR = 0.32–0.12–0.88, p = 0.028) and migraine (OR = 0.10, 95% CI = 0.02–0.49, p = 0.004) samples. Current anxiety disorder correlated with IDD only in migraine patients (OR = 0.19, 95% CI = 0.05–0.77, p = 0.02).
Conclusion: IDD represents a homogenous construct that can be diagnosed in a relevant proportion of patients but it is not typical only of epilepsy, occurring in other central nervous system disorders such as migraine.