The clinical utility of a memory specialization index in epilepsy surgery patients with unilateral hippocampal sclerosis.

OBJECTIVE: Although group studies provide some support for the material-specific model of memory function, there are considerable individual variations in memory function in people with temporal lobe epilepsy, even in those with the same underlying pathology. In this proof-of-concept study, we examined the sensitivity and specificity of a single measure of an individual's relative strength for the encoding of verbal or visual learning. METHODS: Six hundred ninety-two patients with left hemisphere language dominance and unilateral hippocampal sclerosis completed verbal and visual encoding tasks with similar test structures as part of their presurgical evaluation. Three hundred one patients had right hippocampal sclerosis (RHS), and 391 patients had left hippocampal sclerosis (LHS). A memory specialization index (MSI) was calculated by subtracting the Visual Learning z-score from the Verbal Learning z-score. A positive value on the MSI indicates a relative strength in verbal learning. A negative score indicates a relative strength in visual learning. RESULTS: Employing cut-offs of ±1, the MSI had a positive predictive value of 71% (confidence interval [CI] 95% 0.64-0.77) for LHS and 64% (CI 95% 0.55-0.74) for RHS and was superior to the standalone z-scores from the verbal and visual tests in each respect. In the LHS group, the MSI was significantly correlated with age and duration of epilepsy. Older patients who had a longer duration of epilepsy were more likely to demonstrate a similar level of impairment in both verbal and visual learning, with a decreasing discrepancy between the scores on the two tasks over time. SIGNIFICANCE: Our MSI provides a measure with high specificity for RHS. The pattern of strengths and weaknesses in visual and verbal encoding may evolve with age and duration of epilepsy, and clinicians should be aware of these factors when interpreting the lateralizing significance of test scores, particularly in a presurgical setting.

Predicting and preventing psychopathology following temporal lobe epilepsy surgery.

Less than 3% of temporal lobe epilepsy (TLE) surgical outcome studies have investigated the psychiatric sequelae and morbidity associated with surgery. This is disproportionate to the extent of the problem. Variable prevalence rates have been reported for post-surgical depression, anxiety, and interictal psychosis. Until recently, very few studies distinguished de novo postoperative presentations from pre-existing conditions, making it difficult to accurately assess the impact of TLE surgery on psychiatric morbidity. Predictors of de novo postoperative presentations have proved elusive. This current review summarizes the findings from a systematic literature review of the psychiatric morbidity associated with TLE surgery including newly published follow-up data from our own series of 280 surgical patients. A framework for future research, possible pathophysiological mechanisms, and translational models are also discussed.

Pre-operative verbal memory fMRI predicts post-operative memory decline after left temporal lobe resection.

Functional MRI (fMRI) of cognitive tasks depends on technology widely available in the clinical sphere, but has yet to show a role in the investigation of patients. We report here the first demonstration of a clinically valuable role for cognitive fMRI. Temporal lobe epilepsy (TLE) is commonly caused by hippocampal sclerosis and is frequently resistant to drug treatment. Surgical resection of the left hippocampus in this setting can cure seizures, but may produce significant verbal memory decline, which is hard to predict. We report 10 right-handed TLE patients with left hippocampal sclerosis who underwent left hippocampal resection. We compared currently used data for the prediction of post-operative verbal memory decline in such patients with a novel fMRI assessment of verbal memory encoding. Multiple regression analyses showed that fMRI provided the strongest independent predictor of memory outcome after surgery. At the individual subject level, the fMRI data had high positive predictive value for memory decline.

Epilepsy & depression: the effects of comorbidity on hippocampal volume--a pilot study.

Hippocampal sclerosis (HS) is one of the most common pathologies in medically intractable temporal lobe intractable epilepsy. Significant hippocampal volume loss has also been found in patients with chronic depression. Depression is common in chronic epilepsy populations, but the effects of this comorbidity on hippocampal volume are unknown. We examined the hippocampal volumes of 87 patients (n=31 right hippocampal sclerosis, RHS; n=56 left hippocampal sclerosis, LHS). Each subject completed the Hospital Anxiety and Depression Scale (HADS). In the group as a whole, 13 subjects (15%) recorded moderate or severe levels of depression. Depression was more common in the LHS group with 1 in 5 scoring in the moderate or severe range on the HADS (n=11). Depression scores were not significantly correlated with quantitative measures of hippocampal volume in the LHS group. However, higher degrees of hippocampal symmetry were associated with higher levels of depression in the RHS group. This suggests that the left hippocampus may be smaller in depressed patients with RHS, although our numbers were too small to confirm this statistically. Our results suggest that the depression may influence left hippocampal volume in patients with right hippocampal sclerosis. We conclude that the neuroradiological characteristics of patients with epilepsy and chronic depression deserve further examination.