Depression and epilepsy: how closely related are they?

Article abstract Depressive disorders (DDs) are the most common type of psychiatric co-morbidity in patients with epilepsy. They are more likely to occur in patients with partial seizure disorders of temporal and frontal lobe origin and are more frequent among patients with poorly controlled seizures. Despite their relatively high prevalence, DDs remain unrecognized and untreated in a large proportion of patients. This article highlights the evidence of a close association between DDs and epilepsy, beginning with the bi-directional relationship between the two disorders. Not only are patients with epilepsy more likely to experience a DD, but a history of DD preceding the onset of the seizure disorder is more likely to be identified in patients with epilepsy than in a control group. In support of these observations, we review data from animal models of epilepsy showing that decreased activity of serotonin, norepinephrine, dopamine, and GABA facilitate the kindling process of seizure foci, worsen seizure frequency and severity, and are reversed or blocked by antidepressant drugs. Decreased activity of these neurotransmitters is a pivotal pathogenic mechanism of DDs and forms the basis of their pharmacotherapy. Thus, DDs and epilepsy may share common pathogenic mechanisms that facilitate the occurrence of one in the presence of the other. Contrary to long-held beliefs by patients and clinicians alike, in the sense that DDs are a "normal reaction" to the obstacles posed by epilepsy, we review evidence that points to their biologic or endogenous nature. We find a genetic predisposition to DDs, as evidenced by the frequent family history of mood disorders in these patients. Neuroimaging and neuropsychological data support a frontal lobe dysfunction in DDs, and a recent study documents concomitant dysfunction of mesial temporal structures. Depressive disorders have various clinical presentations, some typical of the different types of mood disorders in non-epileptic patients, others constituting rather frequent atypical presentations that can easily go unrecognized. A review of the pharmacologic treatment of DDs in epilepsy highlights the lack of scientific data and points to the empirical form in which these patients have been treated up to the present time. Contrary to clinicians' fears, most antidepressant drugs are safe in patients with epilepsy.