Mood disorder and epilepsy: a neurobiologic perspective of their relationship

Mood disorders are the most frequent psychiatric comorbidity in epilepsy, and in particular in temporal lobe epilepsy. For a long time, depressive disorders were considered to be the expression of a reactive process to the obstacles of a life with epilepsy Data obtained in the last two decades, however, have demonstrated biochemical, neuropathoiogical, and neurophysioiogic changes mediating the development of mood disorders, which in fact can be tested in animal models. Furthermore, there is also evidence that mood disorders and epilepsy have a complex relationship which is bidirectional; that is, not only are patients with epilepsy at greater risk of developing depression, but patients with depression have a higher risk of developing epilepsy. Such a relationship can only be explained by the existence of common pathogenic mechanisms that are operant in both conditions. These include changes in neurotransmitters, such as serotonin, norepinephrine, glutamate, and γ-aminobutyric acid. Such a bidirectional relationship also appears to have important clinical consequences. Indeed, patients with a history of mood disorders are twice as likely to develop pharmacoresistant epilepsy as those without such a history. These data are reviewed in this article.