The relationship of epilepsy syndromes to depression

There has been considerable debate, which is unresolved, as to the association between any particular epilepsy syndrome and depression. It is the case that people with lesional epilepsy from the temporal lobes are more likely to have intractable seizures, and they also are more likely to be taking more extensive medication than those with non-temporal epilepsy, and they may be at increased risk. Thus, some studies have shown patients with temporal lobe epilepsy to be more prone to depression than other groups, but other investigations have failed to confirm this. Examining etiology of epilepsy, Quiske et al. (2000) found that patients with temporal lobe epilepsy who had mesial temporal sclerosis were more likely to report depression. In general terms, there is more agreement that patients with complex partial seizures are more likely to have a depressive disorder (Robertson, 1998).

There are also studies linking frontal lobe dysfunction to the depression of epilepsy. The latter have emerged from investigations using brain imaging (positron emission tomography — PET or single-photon emission-computed tomography — SPECT), and neuropsychological batteries. Hermann et al. (1991) noted that patients with temporal lobe epilepsy and depression were more likely to perform poorly on frontal lobe neuropsychological tasks, especially with a left-sided seizure focus. Schmitz et al. (1997) noted similar frontal changes and localizations using SPECT, and Bromfield et al. (1990) using PET reported that patients with temporal lobe epilepsy and associated depression revealed bilateral reductions of frontal lobe metabolism.

Although these studies, of necessity, were on a limited number of patients, the concordance between the findings does support an anatomical association between temporal lobe epilepsy, depression and frontal lobe dysfunction.

With regards to the temporal lobe association with depression, it is of interest that there are a number of studies outside the field of epilepsy which suggest that hippocampal volume loss is associated with affective disorders (Bremner et al., 2000; Frodl et al., 2002). Thus, although further research in this area is needed, neuroimaging studies are revealing an underlying neurocircuitry of depression in psychiatric patients without a neurological disorder, which includes the hippocampus, thus in keeping with the findings in sub-groups of patients with epilepsy.

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