Are mental distress and cognitive impairment related in temporal lobe epilepsy?

Cognitive impairment and depression often co-exist among patients with epilepsy. However, there is still debate whether depression and cognition are related in patients with temporal lobe epilepsy (TLE). Even if they were related, it is still unclear whether symptoms of depression specifically, or rather symptoms of mental distress in general, have a negative impact on cognition in patients with TLE. In the present study, we examined whether self-rated symptoms of mental distress and of depression are related to different cognitive functions in unilateral TLE.

We retrospectively studied 162 patients undergoing preoperative evaluation for epilepsy surgery (95 patients with left TLE (LTLE) and 67 patients with right TLE (RTLE)). Severity of mental distress and symptoms of depression were measured with the Symptom Checklist-90-Revised (SCL-90-R) and the Beck Depression Inventory (BDI), respectively. Bivariate correlations were calculated between these two measures and neuropsychological measures of verbal recall, figural learning, psychomotor speed, and phonemic word fluency. Due to multiple testing, a corrected level of p < 0.0063 was regarded as significant, only.

Seventeen and 19% of patients reported meaningful mental distress and meaningful symptoms of depression, respectively. Mental distress highly correlated with symptoms of depression (r_s = 0.80). We found no significant correlations of either mental distress or symptoms of depression with measures of cognitive function.

In contrast to some former studies with smaller sample sizes, the present study could not detect a relationship of depression with cognitive impairment in patients with unilateral TLE. Likewise, mental distress and cognition were unrelated in our sample of patients. Our results may argue against theoretical models claiming a causal link between depression and cognitive impairment or a common pathogenic mechanism for these conditions in patients with TLE.