Single-Voxel Proton Magnetic Resonance Spectroscopy of the Thalamus in Idiopathic Epileptic Dogs and in Healthy Control Dogs

The role of magnetic resonance spectroscopy (MRS) in the investigation of brain metabolites in epileptic syndromes in dogs has not been explored systematically to date. The aim of this study was to investigate metabolites in the thalamus in dogs affected by idiopathic epilepsy (IE) with and without antiepileptic drug treatment (AEDT) and to compare them to unaffected controls. Our hypothesis is that similar to humans with generalized epilepsy and loss of consciousness, N-acetyl aspartate (NAA) would be reduced, and glutamate–glutamine (Glx) would be increased in treated and untreated IE in comparison with the control group. In this prospective case–control study, Border Collie (BC) and Greater Swiss Mountain dog (GSMD) were divided into three groups: (1) healthy controls, IE with generalized tonic–clonic seizures with (2) and without (3) AEDT. A total of 41 BC and GSMD were included using 3 Tesla single-voxel proton MRS of the thalamus (PRESS localization, shortest TE, TR = 2000 ms, NSA = 240). After exclusion of 11 dogs, 30 dogs (18 IE and 12 healthy controls) remained available for analysis. Metabolite concentrations were estimated with LCModel using creatine as reference and compared using Kruskal–Wallis and Wilcoxon rank-sum tests. The Kruskal–Wallis test revealed significant differences in the NAA-to-creatine (p = 0.04) and Glx-to-creatine (p = 0.03) ratios between the three groups. The Wilcoxon rank-sum test further showed significant reduction in the NAA/creatine ratio in idiopathic epileptic dogs under AEDT compared to epileptic dogs without AEDT (p = 0.03) and compared to healthy controls (p = 0.03). In opposite to humans, Glx/creatine ratio was significantly reduced in dogs with IE under AEDT compared to epileptic dogs without AEDT (p = 0.03) and controls (p = 0.02). IE without AEDT and healthy controls did not show significant difference, neither in NAA/creatine (p = 0.60), nor in Glx-to-creatine (p = 0.55) ratio. In conclusion, MRS showed changes in dogs with IE and generalized seizures under AEDT, but not in those without AEDT. Based upon these results, MRS can be considered a useful advanced imaging technique for the evaluation of dogs with IE in the clinical and research settings.

Recent Developments in Diagnosis of Epilepsy: Scope of MicroRNA and Technological Advancements

Epilepsy is one of the most common neurological disorders, characterized by recurrent seizures, resulting from abnormally synchronized episodic neuronal discharges. Around 70 million people worldwide are suffering from epilepsy. The available antiepileptic medications are capable of controlling seizures in around 60-70% of patients, while the rest remain refractory. Poor seizure control is often associated with neuro-psychiatric comorbidities, mainly including memory impairment, depression, psychosis, neurodegeneration, motor impairment, neuroendocrine dysfunction, etc., resulting in poor prognosis. Effective treatment relies on early and correct detection of epileptic foci. Although there are currently a few well-established diagnostic techniques for epilepsy, they lack accuracy and cannot be applied to patients who are unsupportive or harbor metallic implants. Since a single test result from one of these techniques does not provide complete information about the epileptic foci, it is necessary to develop novel diagnostic tools. Herein, we provide a comprehensive overview of the current diagnostic tools of epilepsy, including electroencephalography (EEG) as well as structural and functional neuroimaging. We further discuss recent trends and advances in the diagnosis of epilepsy that will enable more effective diagnosis and clinical management of patients.

Diagnostic and prognostic role of proton single-voxel spectroscopy (SVS) in non-lesional epilepsy pediatric patients: prospective controlled study

Background

We aimed to verify the diagnostic and prognostic role of proton single-voxel spectroscopy (SVS) in children with non-lesional epilepsy and its add-on value to conventional MR. The prospective controlled study carried out on the epileptic patients who were regularly following in the pediatric neurology clinic in our university hospital, over the period from July 2017 to July 2018. It compared SVS findings (NAA/Cr, NAA/Cho, and NAA/Cho+Cr ratios) between the case (50 patients) and control group (20 children), between the cases with different seizures semiology and between the patients with intractable and non-intractable epilepsy.

Results

NAA/Cr ratio showed a significant difference between the patients with intractable and non-intractable epilepsy in the basal ganglia (P value 0.005) and white matter (P value 0.043) with cutoff values of 1.5 and 1.9 respectively. A significant difference of NAA/Cho ratio was found between generalized seizures cases and other seizures semiology in basal ganglia (P value 0.012) and cortex (P value <.001). There was no significant difference between the patient and control groups or between generalized seizures cases and the control group.

Conclusion

Proton SVS has limited diagnostic value in non-lesional epilepsy pediatric patients, in differentiation between generalized seizures and other seizure types, but, it has a good prognostic role in predicting patients who will develop intractable epilepsy.

Alterations in Brain Metabolites in Patients with Epilepsy with Impaired Consciousness: A Case-Control Study of Interictal Multivoxel 1H-MRS Findings

BACKGROUND AND PURPOSE

Previous studies have shown perfusion abnormalities in the thalamus and upper brain stem in patients with epilepsy with impaired consciousness. We hypothesized that these areas associated with consciousness will also show metabolic abnormalities. However, metabolic abnormalities in those areas correlated with consciousness has not been characterized with multiple-voxel ¹H-MRS. In this study, we investigated the metabolic alterations in these brain regions and assessed the correlation between seizure features and metabolic alterations.

MATERIALS AND METHODS

Fifty-seven patients with epilepsy and 24 control subjects underwent routine MR imaging and 3D multiple-voxel ¹H-MRS. Patients were divided into 3 subgroups: focal impaired awareness seizures (n = 18), primary generalized tonic-clonic seizures (n = 19), and secondary generalized tonic-clonic seizures (n = 20). The measured metabolite alterations in NAA/Cr, NAA/(Cr + Cho), and Cho/Cr ratios in brain regions associated with the consciousness network were compared between the patient and control groups. ROIs were placed in the bilateral inferior frontal gyrus, supramarginal gyrus, cingulate gyrus, precuneus, thalamus, and upper brain stem. Correlations between clinical parameters (epilepsy duration and seizure frequency) and metabolite alterations were analyzed.

RESULTS

Significantly lower NAA/Cr and NAA/(Cho + Cr) ratios (P < .05 and < .01, respectively) were observed in the bilateral thalamus and upper brain stem in all experimental groups, and significantly high Cho/Cr ratios (P < .05) were observed in the right thalamus in the focal impaired awareness seizures group. There were no significant differences in metabolite ratios among the 3 patient groups (P > .05). The secondary generalized tonic-clonic seizures group showed a negative correlation between the duration of epilepsy and the NAA/(Cr + Cho) ratio in the bilateral thalamus (P < .05).

CONCLUSIONS

Metabolic alterations were observed in the brain stem and thalamus in patients with epilepsy with impaired consciousness.

Neuroimaging of epilepsy

Imaging is pivotal in the evaluation and management of patients with seizure disorders. Elegant structural neuroimaging with magnetic resonance imaging (MRI) may assist in determining the etiology of focal epilepsy and demonstrating the anatomical changes associated with seizure activity. The high diagnostic yield of MRI to identify the common pathological findings in individuals with focal seizures including mesial temporal sclerosis, vascular anomalies, low-grade glial neoplasms and malformations of cortical development has been demonstrated. Positron emission tomography (PET) is the most commonly performed interictal functional neuroimaging technique that may reveal a focal hypometabolic region concordant with seizure onset. Single photon emission computed tomography (SPECT) studies may assist performance of ictal neuroimaging in patients with pharmacoresistant focal epilepsy being considered for neurosurgical treatment. This chapter highlights neuroimaging developments and innovations, and provides a comprehensive overview of the imaging strategies used to improve the care and management of people with epilepsy.

Epilepsies associated with hippocampal sclerosis

Hippocampal sclerosis (HS) is considered the most frequent neuropathological finding in patients with mesial temporal lobe epilepsy (MTLE). Hippocampal specimens of pharmacoresistant MTLE patients that underwent epilepsy surgery for seizure control reveal the characteristic pattern of segmental neuronal cell loss and concomitant astrogliosis. However, classification issues of hippocampal lesion patterns have been a matter of intense debate. International consensus classification has only recently provided significant progress for comparisons of neurosurgical and clinic-pathological series between different centers. The respective four-tiered classification system of the International League Against Epilepsy subdivides HS into three types and includes a term of "gliosis only, no-HS". Future studies will be necessary to investigate whether each of these subtypes of HS may be related to different etiological factors or with postoperative memory and seizure outcome. Molecular studies have provided potential deeper insights into the pathogenesis of HS and MTLE on the basis of epilepsy-surgical hippocampal specimens and corresponding animal models. These include channelopathies, activation of NMDA receptors, and other conditions related to Ca(2+) influx into neurons, the imbalance of Ca(2+)-binding proteins, acquired channelopathies that increase neuronal excitability, paraneoplastic and non-paraneoplastic inflammatory events, and epigenetic regulation promoting or facilitating hippocampal epileptogenesis. Genetic predisposition for HS is clearly suggested by the high incidence of family history in patients with HS, and by familial MTLE with HS. So far, it is clear that HS is multifactorial and there is no individual pathogenic factor either necessary or sufficient to generate this intriguing histopathological condition. The obvious variety of pathogenetic combinations underlying HS may explain the multitude of clinical presentations, different responses to clinical and surgical treatment. We believe that the stratification of neuropathological patterns can help to characterize specific clinic-pathological entities and predict the postsurgical seizure control in an improved fashion.

Neuroimaging in investigation of patients with epilepsy

PURPOSE OF REVIEW

This review discusses the MRI and functional imaging findings in patients with focal seizures, practical ways to improve the detection of subtle lesions, and limitations and pitfalls of the various imaging techniques in this context.

RECENT FINDINGS

A proper MRI investigation of patients with focal epilepsy requires the use of specific protocols, selected based on identification of the region of onset by clinical and EEG information. For practical purposes, the focal epilepsies are divided here into mesial temporal lobe epilepsies and neocortical epilepsies. The majority of patients with mesial temporal lobe epilepsies associated with hippocampal sclerosis undergoing presurgical evaluation will have a clear-cut unilateral atrophic hippocampus with increased T2 signal and a normal-appearing contralateral hippocampus. Among the several types of neocortical lesions, focal cortical dysplasias deserve especial attention because these lesions are often missed on routine MRIs. The focal cortical dysplasias include a gradient of morphologic changes from dysplastic lesions that can be easily identified by conventional MRI techniques to minor structural abnormalities with small areas of discrete cortical thickening and blurring of the gray/white matter interface that often go unrecognized.

SUMMARY

The use of MRI protocols targeted for the study of patients with epilepsy allows the diagnosis of the etiology of epilepsy in most patients with focal seizures. However, in a considerable number of patients with epilepsy, MRI results are considered normal. Although the etiology remains unclear in these cases, the malformations of cortical development (mainly focal cortical dysplasias) have been identified as most likely pathologic substrates. The effort involved in trying to increase the detection of these "invisible" lesions involves the improvement of structural imaging techniques and the combination of metabolic and functional studies, including 18F-fluorodeoxyglucose-positron emission tomography (18F-FDG-PET), ictal single-photon emission computed tomography (SPECT), diffusion MRI, and magnetic resonance spectroscopy (MRS). The methods used to enhance the detection of subtle cortical abnormalities by improving the structural images have addressed two basic aspects of the examination by MRI: signal acquisition and imaging postprocessing.

A proton magnetic resonance spectroscopic study in juvenile absence epilepsy in early stages

PURPOSE

The aim of this study to evaluate the hippocampal, frontal and thalamic lobe functions in the early stage of the juvenile absence epilepsy (JAE) by magnetic resonance proton spectroscopy (MRS).

METHOD

Fourteen patients with juvenile absence epilepsy with typical absence seizures and 10 healthy volunteer controls were included in this study. The diagnosis of the patients was in accordance with EEG findings and seizure semiology. All patients had minimum twice EEG recordings and all had typical 3-Hz generalized spike and slow-wave discharges at least on one EEG. All patients had bilateral MRS of frontal, thalamic and hippocampal regions and NAA, NAA/Cr, NAA/Cho, NAA/Cho+Cr levels were detected.

RESULTS

The mean age was 14.9+/-2.05 and 14.5+/-1.7 of the JAE patients and control subjects, respectively. Mean seizure onset duration were 2.3+/-0.9 years. In patient group the frontal, thalamic and hippocampal NAA/Cr ratios were 1.65, 1.78, 1.47 in right and 1.75, 1.90, 1.42 in left, respectively. While in the control group NAA/Cr ratios were 1.64, 2.42, 1.57 in right and 1.83, 2.44, 1.47 in left, respectively. There weren't any difference in frontal and hippocampal regions, but the bilateral thalamic NAA, NAA/Cr ratios of the patients were significantly lower than control group even in early stages of the disease.

CONCLUSION

The observed reductions in NAA levels and NAA/Cr ratios of bilateral thalamic regions are consistent with epilepsy related excitoxicity as a possible underlying mechanism even in early stage of JAE. However, we believe that to generalize the results of our study a prospective multicenter study is required.

Monovoxel 1H Magnetic Resonance Spectroscopy in the Progression of Gliomas

AIM

Can monovoxel magnetic resonance spectroscopy (MRS) reliably follow tumour progression in low-grade glioma?

MATERIALS AND METHODS

21 patients with low-grade glioma underwent at least 3 MRS.

RESULTS

For progression from a grade II to grade III tumour, a sensitivity of 57.1% and specificity of 60% were observed, with a positive predictive value (PPV) of 48.8% and a negative predictive value (NPV) of 54.5%. For progression under treatment, we obtained a sensitivity of 57.1% by N-acetylaspartate (NAA)/choline (Cho) and myoinositol/creatine (Cr) and a specificity of 100% by Cho/Cr and lipids, with a PPV of 80% and a NPV of 63.6%.

CONCLUSION

We found that NAA/Cho is the best marker of tumour progression before therapy, with a sensitivity of 53.9%. For the therapeutic response, sensitivity was only 28.2%.

Proton magnetic resonance spectroscopy study of bilateral thalamus in juvenile myoclonic epilepsy

PURPOSE

To investigate neuronal dysfunction in the thalami of juvenile myoclonic epilepsy (JME) by using proton magnetic resonance spectroscopy (MRS).

METHODS

We performed single-voxel proton MRS over the right and the left thalami of 15 consecutive patients (10 women, 5 men) with JME (mean age 20.3 years) and 16 healthy volunteers (10 women, 6 men) (mean age 24.5 years). All patients had seizure onset in late childhood-teenage, normal neurologic examination, typical electroencephalogram (EEG) of JME and normal magnetic resonance imaging (MRI). We determined N-acetylaspartate (NAA) values and NAA over creatine-phosphocreatine (Cr) values. Mann-Whitney U-test was used to evaluate group differences.

RESULTS

Group analysis showed that echo time (TE) 270 integral value of NAA over left thalamus were significantly decreased in JME patients as compared with controls (34.6033+/-15.8386; 48.0362+/-22.2407, respectively, P=0.019). Also group analysis showed that thalami NAA/Cr ratios were significantly decreased in JME patients (right side, 2.21+/-1.07; left side 2.00+/-0.72) as compared with controls (right side, 3.45+/-1.50; left side, 3.08+/-1.60; P=0.011 and P=0.030, respectively).

CONCLUSION

In the previous studies, NAA values in patients with JME found that they were not statistically lower in thalami than control group. But, in our study, NAA value was found low as well. It has been known that NAA is a neuronal marker and hence it is a valuable metabolite in the neuron physiopathology. As a result, in the patients with JME we tried to support the theory that the underlying mechanism of the generalized seizures was the abnormal thalamocortical circuity, determining the thalamic neuronal dysfunction in MRS statistically.

Metabolic brain imaging by magnetic resonance

Novel magnetic resonance methods have been developed to noninvasively measure biochemical compounds in the human brain as guided by magnetic resonance imaging. Together, these methods are referred to as magnetic resonance spectroscopy (MRS) and can be divided into three major categories: single voxel MRS, magnetic resonance spectroscopic imaging and dynamic MRS, which is a novel adaption of the first method. The techniques and range of biochemical compounds that can be measured safely and serially are advancing rapidly, with many technical developments. MRS methods, when applied to the human brain, have an important diagnostic role, help monitor and guide therapeutic interventions and provide a tool to investigate the mechanisms of neuropsychiatric disease processes, normal brain development and neuropharmacology in vivo.

Glutamate metabolism in epilepsy: 13C-magnetic resonance spectroscopy observation in the human brain

To clarify changes in glutamate metabolism in the brain with chronic epileptic activities, 13C-magnetic resonance spectroscopy observation of glutamate and glutamine synthesis after oral administration of [1-13C] glucose (Glc C1) (0.75 g/kg) was performed in intractable occipital lobe epilepsy patients (n=5) and controls (n=10). 1H[13C]-spectra were obtained from two voxels of 64 ml placed on the bilateral parieto-occipital lobes of the study participants. Time courses for 13C-incorporation into 4-glutamate and 3-glutamate (Glu C4, C3) and 4-glutamine (Gln C4) were obtained and the concentrations of Glu C4, C3 and Gln C4 at the time between 120 and 150 min after Glc C1 administration was calculated. Concentration of Gln C4 was increased in the epilepsy patients [control: 0.39 mM (SD 0.14), epilepsy: 0.60 mM (SD 0.15), P<0.05], whereas those of Glu C4 and Glu C3 were not. The present study revealed increased glutamine synthesis compared with glutamate formation in a widespread cortical area with sustained epileptiform activities, possibly a result of chronic excessive glutamate release from neurons and subsequent uptake into astrocytes.

Evidence of reversible axonal dysfunction in systemic lupus erythematosus: a proton MRS study

Our objective was to investigate axonal dysfunction in patients with systemic lupus erythematosus (SLE) using proton magnetic resonance spectroscopy (1H-MRS). We studied prospectively 90 SLE patients (mean age of 32.5 years) and 23 normal volunteers (mean age of 33.8 years). We performed single voxel proton MRS using point resolved spectroscopy sequence over the superior-posterior region of the corpus callosum. We measured signals from N-acetyl compounds [N-acetylaspartate (NAA)] at 2.01 p.p.m., choline-based compounds (Cho) at 3.2 p.p.m. and creatine and phosphocreatine containing compounds (Cr) at 3.0 p.p.m. and determined NAA/Cr ratios. After 12 months, MRI and MRS were repeated in 50 patients and 9 volunteers. Patients were divided according to disease activity (measured by SLE disease activity index) during initial and follow-up MRS. We performed paired t-test and ANOVA with Tukey's post hoc comparisons to evaluate group differences. At study entry, 29 patients had active SLE with involvement of central nervous system (CNS) and 28 patients had active SLE without CNS manifestations. A total of 14 patients had inactive SLE with past CNS presentation, and 19 had inactive SLE without history of CNS involvement. NAA/Cr ratios were significant lower in patients with active SLE, independently of CNS involvement, when compared with patients with inactive SLE (P = 0.005) and controls (P = 0.01). We observed a significant increase in NAA/Cr ratio in 15 patients who had active SLE at initial MRS and inactive SLE at follow-up (P = 0.04). In 10 patients with active SLE both at initial and at follow-up MRS we observed a reduction in NAA/Cr ratio (P = 0.02). By contrast, there was a significant reduction of NAA/Cr ratio in 15 patients who had inactive SLE at initial MRS and active SLE at follow-up (P = 0.001). In 10 patients with inactive SLE both at initial and at follow-up MRS NAA/Cr ratio did not change (P = 0.2). This study shows evidence of axonal dysfunction in patients with active SLE, independently of CNS manifestations that may be reversible, at least in part, during periods of inactivity of disease.

Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis

Experts discussed the definition, natural history, pathologic features, pathogenesis, electroclinical, neurophysiological, neuropsychological, structural and functional imaging findings, as well as surgical outcome in mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS). After a long-lasting consensus process the ILAE Commission Neurosurgery of epilepsy accepted the resulting conclusions as state-of-the art report on MTLE-HS. The majority of contributors considered MTLE-HS to represent a sufficient cluster of signs and symptoms to make up a syndromic diagnostic entity.

Thalamic Dysfunction in Juvenile Myoclonic Epilepsy: A Proton MRS Study

PURPOSE

To investigate neuronal dysfunction in the thalami of patients with juvenile myoclonic epilepsy (JME) by using proton magnetic resonance spectroscopy (MRS).

METHODS

We performed single-voxel proton MRS over the right and the left thalami of 10 consecutive patients (five women) with JME (mean age, 31.6 years) and 10 age-matched healthy volunteers (five men). All patients had seizure onset in late childhood-teenage, normal neurologic examination, typical EEG of JME, and normal high-resolution MR imaging (MRI). We determined ratios of N-acetylaspartate (NAA) over creatine-phosphocreatine (Cr). Values <2 standard deviations from controls were considered abnormal. We performed analysis of variance to evaluate group differences.

RESULTS

Group analysis showed that thalami NAA/Cr ratios were significantly decreased in JME patients (left side, 1.58 +/- 0.26; right side, 1.5 +/- 0.15) as compared with controls (left side, 1.98 +/- 0.18; right side, 1.88 +/- 0.15; p = 0.001 and p = 0.007, respectively). Individual analysis showed that nine of the 10 patients had abnormal NAA/Cr in at least one of the thalami.

CONCLUSIONS

This study shows evidence of neuronal dysfunction in the thalami of patients with JME, which may have relevance for the mechanisms of seizure generation in this form of generalized epilepsy.

Neuronal and glial metabolite content of the epileptogenic human hippocampus

Mesial temporal lobe epilepsy is characterized by hippocampal atrophy, hypometabolism, and decreased N-acetylaspartate, often attributed to neuron loss and gliosis. Twenty hippocampal specimens were obtained during temporal lobectomy and frozen quickly. Perchloric acid extracts of the small metabolites were analyzed by proton magnetic resonance spectroscopy. There were no significant associations between hippocampal neuron loss and the cellular content of N-acetylaspartate, glutamate, GABA, glutamine, or aspartate. The mean metabolite content of hippocampi with less than 30% of neurons remaining was the same as those with greater than 65% of neurons surviving. Mean N-acetylaspartate levels were below those reported by in vivo studies of control subjects. The highest and the lowest glutamate concentrations were seen in specimens with the worst neuron loss. A highly significant association between hippocampal N-acetylaspartate and glutamate content was seen with weak associations between N-acetylaspartate and aspartate and glutamate and aspartate. The hippocampal content of N-acetylaspartate, glutamate, GABA, glutamine, and aspartate is altered minimally by severe neuron loss in mesial temporal lobe epilepsy. The epileptic human hippocampus has increased intracellular glutamate content that may contribute to the epileptogenic nature of hippocampal sclerosis.