Chronic temporal lobe epilepsy: spatial extent and degree of metabolic dysfunction studied with magnetic resonance spectroscopy (MRS)

The medial temporal lobe epilepsy is a bilateral disease – novel aspects

Introduction.Medial temporal lobe epilepsy (MTLE) is the most frequent form of epilepsy in adulthood. It is classified as local/regional epilepsy. However, there is increasing evidence of the involvement of both temporal lobes and this provides abundant arguments to question this view, and consider MTLE as one of the typical bilateral system epilepsies.

Aim.To provide a contemporary review of medial temporal lobe epilepsy, discussing the bilateral aspects, with reference to epilepsy surgery.

Methods.A literature review and a resume of the author’s own experiences with MTLE patients.

Results.Recent electrophysiological and neuroimaging data provide convincing data supporting that MTLE is a bilateral disease. The uni-and bilateral features form a continuum and the participation rate of the two temporal lobes determine course and surgical perspective of the individual patient.

Conclusions.The contradictory data of invasive presurgical evaluations of MTLE patients suggest that there need to identify further indicatory markers of bilaterality and thus change the presurgical evaluation from the non-invasive towards the invasive ways. The mechanisms of the interrelationship between the two temporal lobes in MTLE warrants further research.

Epilepsy as progressive disorders: what is the evidence that can guide our clinical decisions and how can neuroimaging help?

There is evidence that some types of epilepsy progress over time, and an important part of this knowledge has derived from neuroimaging studies. Different authors have demonstrated structural damage more pronounced in individuals with a longer duration of epilepsy, and others have been able to quantify this progression over time. However, others have failed to demonstrate progression possibly due to the heterogeneity of individuals evaluated. Currently, temporal lobe epilepsy associated with hippocampal sclerosis is regarded as a progressive disorder. Conversely, for other types of epilepsy, the evidence is not so clear. The causes of this damage progression are also unknown although there is consistent evidence that seizure is one of the mechanisms. The conflicting data about epilepsy progression can be a challenge for clinical decisions for an individual patient. Studies with homogenous groups and longer follow-up are necessary for appropriate conclusions about the real burden of damage progression in epilepsies, and neuroimaging will be essential in this context.

Correlation study of optimized voxel-based morphometry and (1)H MRS in patients with mesial temporal lobe epilepsy and hippocampal sclerosis

PURPOSE

: To assess whether structural and metabolic brain abnormalities are correlated in MTLE/HS syndrome.

METHODS

: Optimized voxel-based morphometry (VBM) of gray matter concentration (GMC) and gray matter volume (GMV) and proton magnetic resonance spectroscopy measurements from both-sided hippocampal and thalamic regions were performed in 20 MTLE/HS patients and 20 sex- and age-matched healthy controls. The local GMC and GMV values were calculated in both the affected and unaffected hippocampi and ipsilateral and contralateral thalami in patients and healthy subjects, and these were compared. VBM variables and NAA, NAA/Cr and NAA/(Cr+Cho) values from the investigated brain regions were correlated.

RESULTS

: (1) Analysis revealed significantly more extensive GMV reduction than GMC reduction in patients' affected hippocampus. In addition, significant GMV reduction was observed in the ipsilateral thalamus in MTLE/HS patients. (2) Significant decreases in all VBM and MRS variables were revealed in the affected hippocampus. Whilst practically normal GMC values were revealed in patients' both-sided thalamic regions, a significant decrease in local GMV and metabolic measurements were found in the patients' ipsilateral thalamus. (3) Pearson's correlations between structural and metabolic abnormalities were significant for the ipsilateral thalamus only.

CONCLUSION

: Structural and metabolic abnormalities as detected by optimized voxel-based morphometry and (1)H MRS in hippocampal and thalamic regions are only partially correlated in MTLE/HS patients. It seems therefore reasonable that both methods reflect different aspects of brain pathology, which, at least to some degree, might be independently ongoing.

Magnetic resonance spectroscopic imaging detects abnormalities in normal-appearing frontal lobe of patients with Sturge-Weber syndrome

BACKGROUND

In Sturge-Weber syndrome (SWS), structural MRI abnormalities are most common in the posterior brain regions. Frontal lobe involvement increases the risk of motor impairment. The goal of this study was to determine whether Magnetic Resonance Spectroscopic Imaging (MRSI) can improve detection of frontal lobe involvement in children with SWS.

METHODS

Sixteen children (age: .9-10.4 years) with unilateral SWS underwent MRI with MRSI prospectively. N-acetyl-aspartate (NAA) and choline asymmetries in the posterior and frontal regions were measured.

RESULTS

Eight children presented normal-appearing frontal lobes on conventional MRI, but 7 of them showed abnormal NAA and/or choline content in the frontal lobe of the affected hemisphere. Lower frontal lobe gray matter NAA was associated with earlier onset of seizures (r= .76; P= .04) and impaired motor function (r=-.89, P < .001). Frontal NAA asymmetry was an independent predictor of motor function in a regression analysis (P= .01)

CONCLUSION

MRSI is more sensitive than conventional structural MRI for detection of frontal lobe involvement in SWS. Decreased frontal lobe NAA is an excellent predictor of motor functions. Thus, MRSI can provide complementary information for the assessment of normal-appearing brain regions, and may assist prognosis evaluation in children with SWS.

Proton MR spectroscopy of metabolite concentrations in temporal lobe epilepsy and effect of temporal lobe resection

PURPOSE

To use proton Magnetic Resonance Spectroscopy (MRS) to measure in vivo temporal lobe GABA and glutamate plus glutamine (GLX) concentrations in patients with temporal lobe epilepsy (TLE) attributable to unilateral hippocampal sclerosis (HS) before and following anterior temporal lobe resection (ATLR).

METHODS

We obtained quantitative short echo time MRS in both temporal lobes of 15 controls and 16 patients with TLE and HS, and repeat spectra in 10 patients after ATLR. We measured the concentrations of N-acetyl aspartate+N-acetyl aspartyl-glutamate (NAAt), creatine plus phosphocreatine (Cr), and glutamate+glutamine (GLX) using a metabolite-nulled sequence designed to minimize macromolecule artifact. GABA concentrations were measured using a previously described double quantum filter.

RESULTS

In patients with TLE, NAAt/Cr was reduced in ipsilateral and contralateral temporal lobes. No significant variation in GLX/Cr or GABA+/Cr was evident in any group although GABA+/Cr was highest in the ipsilateral temporal lobe in TLE. After ATLR there was a trend to normalization of NAAt/Cr in the contralateral temporal lobe but no change in individual metabolite concentrations, GLX/Cr or GABA+/Cr compared to pre-surgery levels.

DISCUSSION

Temporal lobe epilepsy was associated with bilateral reduction in NAAt/Cr but not significant abnormality in GABA+/Cr or GLX/Cr. Normalization of NAAt/Cr in the contralateral temporal lobe was seen following successful ATLR.

Differential neuropsychological test sensitivity to left temporal lobe epilepsy

We examined the sensitivity of the Rey Auditory Verbal Learning Test (AVLT), California Verbal Learning Test (CVLT), Boston Naming Test (BNT), and Multilingual Aphasia Examination Visual Naming subtest (MAE VN) to lateralized temporal lobe epilepsy (TLE) in patients who subsequently underwent anterior temporal lobectomy. For the AVLT (n = 189), left TLE patients performed more poorly than their right TLE counterparts [left TLE = 42.9 (10.6), right TLE = 47.7 (9.9); p < .002 (Cohen's d = .47)]. Although statistically significant, the CVLT group difference (n = 212) was of a smaller magnitude [left LTE = 40.7 (11.1), right TLE = 43.8 (9.9); (p < .03, Cohen's d = .29)] than the AVLT. Group differences were also present for both measures of confrontation naming ability [BNT: left LTE = 43.1 (8.9), right TLE = 48.1 (8.9); p < .001 (Cohen's d = .56); MAE VN: left TLE = 42.2, right TLE = 45.6, p = .02 (Cohen's d = .36)]. When these data were modeled in independent logistic regression analyses, the AVLT and BNT both significantly predicted side of seizure focus, although the positive likelihood ratios were modest. In the subset of 108 patients receiving both BNT and AVLT, the AVLT was the only significant predictor of seizure laterality, suggesting individual patient variability regarding whether naming or memory testing may be more sensitive to lateralized TLE.

The neuroprotective role of creatine

Significant progress has been made in identifying neuroprotective agents and their translation to patients with neurological disorders. While the direct causative pathways of neurodegeneration remain unclear, they are under great clinical and experimental investigation. There are a number of interrelated pathogenic mechanisms triggering molecular events that lead to neuronal death. One putative mechanism reported to play a prominent role in the pathogenesis of neurological diseases is impaired energy metabolism. If reduced energy stores play a role in neuronal loss, then therapeutic strategies that buffer intracellular energy levels may prevent or impede the neurodegenerative process. Recent studies suggest that impaired energy production promotes neurological disease onset and progression. Sustained ATP levels are critical to cellular homeostasis and may have both direct and indirect influence on pathogenic mechanisms associated with neurological disorders. Creatine is a critical component in maintaining cellular energy homeostasis, and its administration has been reported to be neuroprotective in a wide number of both acute and chronic experimental models of neurological disease. In the context of this chapter, we will review the experimental evidence for creatine supplementation as a neurotherapeutic strategy in patients with neurological disorders, including Huntington's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Alzheimer's disease, as well as in ischemic stroke, brain and spinal cord trauma, and epilepsy.

Decrease of NAA with aging outside the seizure focus in mesial temporal lobe epilepsy--a proton-MRS study at 3 Tesla

There is evidence that chronic pharmacoresistant temporal lobe epilepsy (TLE) is a progressive disorder accompanied by mental deterioration. We investigated effects of aging on cerebral N-acetyl-aspartate (NAA) concentrations in the temporal lobe of 12 patients with pharmacoresistant mesial TLE (mTLE) and 22 healthy controls by means of proton-magnetic resonance spectroscopy ((1)H-MRS) at 3 T. Furthermore, we calculated correlations between NAA concentrations and measures of verbal and figural memory in patients. In mTLE patients but not in healthy controls the concentration of NAA in the lateral temporal lobe was negatively correlated with age. In patients with mTLE NAA in left lateral temporal voxels correlated with verbal memory. NAA in medial temporal voxels did not correlate with age or neuropsychological measures. Significant decrease of NAA with age in the lateral temporal lobe of patients with mTLE provides evidence for progressive neuronal dysfunction with aging. NAA is a marker of neuronal integrity since it correlates with verbal memory.

Do Early Hippocampal Imaging Changes Predict Later Sclerosis?

Acute Symptomatic Seizures and Hippocampus Damage: DWI and MRS Findings. Parmar H, Lim SH, Tan NC, Lim CC. Neurology 2006;66:1732–1735. The authors describe diffusion-weighted imaging (DWI) and magnetic resonance spectroscopy (MRS) changes in the hippocampus within 48 h of acute symptomatic seizures or status epilepticus in 12 patients. DWI showed increased signal and a decreased apparent diffusion coefficient (ADC) in all patients, with corresponding lactate detected on MRS in six patients and EEG seizure activity in nine patients. On follow-up, the atrophic hippocampus had an increased ADC in six patients. DWI and MRS may predict development of hippocampal sclerosis.