Executive Dysfunction in Idiopathic Depression vs Epilepsy-associated Depression

Researchers affiliated with the Warren Alpert Medical School of Brown University and Rhode Island Hospital in Providence recently reported that cognitive impairment, which is observed in many patients with temporal lobe epilepsy, is also associated with symptoms of depression. These findings we published in The Journal of Neuropsychiatry and Clinical Neurosciences.

It is known that patients diagnosed with temporal lobe epilepsy present with dysfunction across several cognitive domains, including deficits in working and modality-specific memory, reduced cognitive flexibility, information-processing speed and problem solving ability, impaired attention and concentration, as well as impaired executive function. According to the authors, “detection of executive dysfunction in temporal lobe epilepsy is of particular importance given its strong association with functional impairment and disability.”

Accumulating evidence also points to an association between symptoms of depression and cognitive dysfunction. More specifically, individuals diagnosed with major depressive disorder present with impairments in higher order cognitive abilities including attention, working memory, visual learning, and reasoning and problem solving skills.

To examine the association between depressive symptoms and deficits in executive function, investigators recruited individuals diagnosed with temporal lobe epilepsy only (n=29), temporal lobe epilepsy with comorbid depression (n=22), and depression only (n=31). Participants were classified based on their responses on the Mini International Neuropsychiatric Interview, and the 17-item Hamilton Depression Rating Scale (HAM-D).

Investigators also employed the following tests: 1) trail-making test, to evaluate motor speed and cognitive flexibility; 2) verbal fluency test, to assess the ability to generate words as quickly as possible; 3) design fluency test, to measure visual productivity and cognitive flexibility; 4) color-word interference test, to assess processing speed, inhibition, and cognitive flexibility; 5) sorting test, to examine problem-solving abilities and concept formation; 6) word context test, to test deductive reasoning/abstractions; and, 7) proverb test, to test verbal abstraction.

Results are in line with previous findings and show that individuals diagnosed with temporal lobe epilepsy perform significantly more poorly on tests designed to assess executive function ability. Also, antiepileptic drug polytherapy in this sample was associated with poorer performance on letter fluency, design fluency, and word context tests. With regard to symptoms of depression, participants with comorbid temporal lobe epilepsy and depression performed significantly worse only on tasks designed to examine verbal mental flexibility. In contrast, individuals with depression only (ie, without temporal lobe epilepsy) showed impairments in tasks designed to measure motor speed and visually mediated executive functions.

Taken together, it appears that depressive symptoms do contribute to executive dysfunction among persons with temporal lobe epilepsy, but “the types of deficits associated with depression in temporal lobe epilepsy may be distinct from those with idiopathic depression,” the authors concluded in their publication.

Reference

Galioto R, Tremont G, Blum AS, et al. Depressive symptoms contribute to executive deficits in temporal lobe epilepsy. J Neuropsychiatry Clin Neurosci. 2016. doi: 10.1176/appi.neuropsych.16040064. [Epub ahead of print]