Volumetric Evidence of Bilateral Damage in Unilateral Mesial Temporal Lobe Epilepsy

Right and left mesial temporal lobe seizures in one patient: bona fide semiological, interictal, ictal, and MRI evidence

We present the case of a 36-year-old patient with bilateral independent manual automatisms associated with seizures coming independently from the left and right temporal lobes, as documented by surface EEG ictal recordings. An MRI showed evidence of bilateral mesial temporal sclerosis, more prominent on the right side. We speculate whether clinical semiology (along with the ictal EEG and imaging findings) discourages the pursuit of invasive monitoring, leading to more aggressive medical management in this particular case.

Neurometabolism in human epilepsy

PURPOSE

Because of the large and continuous energetic requirements of brain function, neurometabolic dysfunction is a key pathophysiologic aspect of the epileptic brain. Additionally, neurometabolic dysfunction has many self-propagating features that are typical of epileptogenic processes, that is, where each occurrence makes the likelihood of further mitochondrial and energetic injury more probable. Thus abnormal neurometabolism may be not only a chronic accompaniment of the epileptic brain, but also a direct contributor to epileptogenesis.

METHODS

We examine the evidence for neurometabolic dysfunction in epilepsy, integrating human studies of metabolic imaging, electrophysiology, microdialysis, as well as intracranial EEG and neuropathology.

RESULTS

As an approach of noninvasive functional imaging, quantitative magnetic resonance spectroscopic imaging (MRSI) measured abnormalities of mitochondrial and energetic dysfunction (via 1H or 31P spectroscopy) are related to several pathophysiologic indices of epileptic dysfunction. With patients undergoing hippocampal resection, intraoperative 13C-glucose turnover studies show a profound decrease in neurotransmitter (glutamate-glutamine) cycling relative to oxidation in the sclerotic hippocampus. Increased extracellular glutamate (which has long been associated with increased seizure likelihood) is significantly linked with declining energetics as measured by 31P MR, as well as with increased EEG measures of Teager energy, further arguing for a direct role of glutamate with hyperexcitability.

DISCUSSION

Given the important contribution that metabolic performance makes toward excitability in brain, it is not surprising that numerous aspects of mitochondrial and energetic state link significantly with electrophysiologic and microdialysis measures in human epilepsy. This may be of particular relevance with the self-propagating nature of mitochondrial injury, but may also help define the conditions for which interventions may be developed.

Bilateral white matter diffusion changes persist after epilepsy surgery

PURPOSE

Bilateral white matter diffusion tensor imaging (DTI) abnormalities have been reported in patients with temporal lobe epilepsy (TLE) and unilateral mesial temporal sclerosis (MTS), but it is unknown whether these are functional or structural changes. We performed a longitudinal study in patients with unilateral MTS who were seizure-free for 1 year after surgery to determine whether the observed presurgical white matter diffusion abnormalities were reversible.

METHODS

Eight TLE patients with unilateral MTS who were seizure-free after anterior temporal resection and 22 healthy subjects were recruited. DTI was performed before surgery and at 1-year follow-up. Tractography and region-of-interest (ROI) analyses were performed in the fornix, cingulum, genu, and splenium of the corpus callosum and external capsules. Diffusion tensor parameters were compared between groups and before and after surgery in the patient group.

RESULTS

The fornix, cingulum, and external capsules showed preoperative bilateral abnormal diffusion parameters (i.e., decreased diffusion anisotropy and increased mean and perpendicular diffusivities). The fornix and cingulum ipsilateral to the resected mesial temporal structures showed signs of wallerian degeneration at 1-year follow-up. The contralateral tracts of the fornix, cingulum, and external capsules, as well as the genu of the corpus callosum, failed to show a normalization of their diffusion parameters.

CONCLUSIONS

The irreversibility of the white matter DTI abnormalities on seizure freedom suggests underlying structural abnormalities (e.g., axonal/myelin degradation) as opposed to functional changes (e.g., fluid shifts due to seizures) in the white matter.

Epilepsy

PURPOSE OF REVIEW

To provide a critical review of studies published between December 2005 and November 2006, and detect the advances of basic and clinical research in epilepsy.

RECENT FINDINGS

The complexity of the mechanisms underlying epileptogenesis and drug resistance was repeatedly highlighted. Seizure diagnosis and classification are still difficult, despite the use of valid and reliable instruments. Even well defined epilepsy syndromes may exhibit complex genetic patterns and atypical electroencephalogram features. Low prevalence rates of active epilepsy have been reported from several countries, suggesting underreporting for sociocultural reasons. Several pregnancy and neonatal factors can be found to increase the risk of epilepsy when accurate data are available from well defined populations. Early remission of seizures does not always predict terminal remission after prolonged follow-up. Cognitive regression may be associated with the presence of interictal electroencephalographic epileptiform abnormalities. A Cochrane review showed lamotrigine to be less frequently withdrawn than carbamazepine. However, these findings are contrasted by clinical practice, which showed no individual drug to be more likely to confer seizure freedom than any other.

SUMMARY

Recent research highlights the complexity of the mechanisms of epileptogenesis and drug response, and the difficulties with the classification of epilepsy into separate phenotypic categories.