Predicting posttraumatic epilepsy with MRI: prospective longitudinal morphologic study in adults

Insights into epileptogenesis from post-traumatic epilepsy

Post-traumatic epilepsy (PTE) accounts for 5% of all epilepsies. The incidence of PTE after traumatic brain injury (TBI) depends on the severity of injury, approaching one in three in groups with the most severe injuries. The repeated seizures that characterize PTE impair neurological recovery and increase the risk of poor outcomes after TBI. Given this high risk of recurrent seizures and the relatively short latency period for their development after injury, PTE serves as a model disease to understand human epileptogenesis and trial novel anti-epileptogenic therapies. Epileptogenesis is the process whereby previously normal brain tissue becomes prone to recurrent abnormal electrical activity, ultimately resulting in seizures. In this Review, we describe the clinical course of PTE and highlight promising research into epileptogenesis and treatment using animal models of PTE. Clinical, imaging, EEG and fluid biomarkers are being developed to aid the identification of patients at high risk of PTE who might benefit from anti-epileptogenic therapies. Studies in preclinical models of PTE have identified tractable pathways and novel therapeutic strategies that can potentially prevent epilepsy, which remain to be validated in humans. In addition to improving outcomes after TBI, advances in PTE research are likely to provide therapeutic insights that are relevant to all epilepsies.

The Renin Angiotensin System as a Therapeutic Target in Traumatic Brain Injury

Traumatic brain injury (TBI) is a major public health problem, with limited pharmacological options available beyond symptomatic relief. The renin angiotensin system (RAS) is primarily known as a systemic endocrine regulatory system, with major roles controlling blood pressure and fluid homeostasis. Drugs that target the RAS are used to treat hypertension, heart failure and kidney disorders. They have now been used chronically by millions of people and have a favorable safety profile. In addition to the systemic RAS, it is now appreciated that many different organ systems, including the brain, have their own local RAS. The major ligand of the classic RAS, Angiotensin II (Ang II) acts predominantly through the Ang II Type 1 receptor (AT1R), leading to vasoconstriction, inflammation, and heightened oxidative stress. These processes can exacerbate brain injuries. Ang II receptor blockers (ARBs) are AT1R antagonists. They have been shown in several preclinical studies to enhance recovery from TBI in rodents through improvements in molecular, cellular and behavioral correlates of injury. ARBs are now under consideration for clinical trials in TBI. Several different RAS peptides that signal through receptors distinct from the AT1R, are also potential therapeutic targets for TBI. The counter regulatory RAS pathway has actions that oppose those stimulated by AT1R signaling. This alternative pathway has many beneficial effects on cells in the central nervous system, bringing about vasodilation, and having anti-inflammatory and anti-oxidative stress actions. Stimulation of this pathway also has potential therapeutic value for the treatment of TBI. This comprehensive review will provide an overview of the various components of the RAS, with a focus on their direct relevance to TBI pathology. It will explore different therapeutic agents that modulate this system and assess their potential efficacy in treating TBI patients.

Novel Approaches to Prevent Epileptogenesis After Traumatic Brain Injury

Traumatic brain injury (TBI) is defined as an alteration in brain function or other evidence of brain pathology caused by an external force. When epilepsy develops following TBI, it is known as post-traumatic epilepsy (PTE). PTE occurs in a subset of patients suffering from different types and severities of TBI, occurs more commonly following severe injury, and greatly impacts the quality of life for patients recovering from TBI. Similar to other types of epilepsy, PTE is often refractory to drug treatment with standard anti-seizure drugs. No therapeutic approaches have proven successful in the clinic to prevent the development of PTE. Therefore, novel treatment strategies are needed to stop the development of PTE and improve the quality of life for patients after TBI. Interestingly, TBI represents an excellent clinical opportunity for intervention to prevent epileptogenesis as typically the time of initiation of epileptogenesis (i.e., TBI) is known, the population of at-risk patients is large, and animal models for preclinical studies of mechanisms and treatment targets are available. If properly identified and treated, there is a true opportunity to prevent epileptogenesis after TBI and stop seizures from ever happening. With that goal in mind, here we review previous attempts to prevent PTE both in animal studies and in humans, we examine how biomarkers could enable better-targeted therapeutics, and we discuss how genetic variation may predispose individuals to PTE. Finally, we highlight exciting new advances in the field that suggest that there may be novel approaches to prevent PTE that should be considered for further clinical development.

Viral infections and their relationship to neurological disorders

The chronic dysfunction of neuronal cells, both central and peripheral, a characteristic of neurological disorders, may be caused by irreversible damage and cell death. In 2016, more than 276 million cases of neurological disorders were reported worldwide. Moreover, neurological disorders are the second leading cause of death. Generally, the etiology of neurological diseases is not fully understood. Recent studies have related the onset of neurological disorders to viral infections, which may cause neurological symptoms or lead to immune responses that trigger these pathological signs. Currently, this relationship is mostly based on epidemiological data on infections and seroprevalence of patients who present with neurological disorders. The number of studies aiming to elucidate the mechanism of action by which viral infections may directly or indirectly contribute to the development of neurological disorders has been increasing over the years but these studies are still scarce. Comprehending the pathogenesis of these diseases and exploring novel theories may favor the development of new strategies for diagnosis and therapy in the future. Therefore, the objective of the present study was to review the main pieces of evidence for the relationship between viral infection and neurological disorders such as Alzheimer's disease, Parkinson's disease, Guillain-Barré syndrome, multiple sclerosis, and epilepsy. Viruses belonging to the families Herpesviridae, Orthomyxoviridae, Flaviviridae, and Retroviridae have been reported to be involved in one or more of these conditions. Also, neurological symptoms and the future impact of infection with SARS-CoV-2, a member of the family Coronaviridae that is responsible for the COVID-19 pandemic that started in late 2019, are reported and discussed.

Multiplex Networks to Characterize Seizure Development in Traumatic Brain Injury Patients

Traumatic brain injury (TBI) may cause secondary debilitating problems, such as post-traumatic epilepsy (PTE), which occurs with unprovoked recurrent seizures, months or even years after TBI. Currently, the Epilepsy Bioinformatics Study for Antiepileptogenic Therapy (EpiBioS4Rx) has been enrolling moderate-severe TBI patients with the goal to identify biomarkers of epileptogenesis that may help to prevent seizure occurrence and better understand the mechanism underlying PTE. In this work, we used a novel complex network approach based on segmenting T1-weighted Magnetic Resonance Imaging (MRI) scans in patches of the same dimension (network nodes) and measured pairwise patch similarities using Pearson's correlation (network connections). This network model allowed us to obtain a series of single and multiplex network metrics to comprehensively analyze the different interactions between brain components and capture structural MRI alterations related to seizure development. We used these complex network features to train a Random Forest (RF) classifier and predict, with an accuracy of 70 and a 95% confidence interval of [67, 73%], which subjects from EpiBioS4Rx have had at least one seizure after a TBI. This complex network approach also allowed the identification of the most informative scales and brain areas for the discrimination between the two clinical groups: seizure-free and seizure-affected subjects, demonstrating to be a promising pilot study which, in the future, may serve to identify and validate biomarkers of PTE.

Diagnosis and long-term management of post-traumatic seizures in a white-crowned pionus (Pionus senilis)

CASE DESCRIPTION

A 13-year-old female white-crowned pionus (Pionus senilis) was examined because of seizures 22 months after it was treated for a traumatic brain injury (TBI) characterized by vision loss, hemiparesis, nystagmus, circling, and head tilt.

CLINICAL FINDINGS

Bloodwork performed during the initial seizure workup revealed hypercalcemia and hypercholesterolemia, which were attributed to vitellogenesis given the bird's previous egg-laying history and recent onset of reproductive behavior. Magnetic resonance imaging of the brain revealed diffuse right pallium atrophy with multifocal hydrocephalus ex vacuo, which were believed to be the result of the previous TBI. Findings were most consistent with post-traumatic seizures (PTS).

TREATMENT AND OUTCOME

Levetiracetam (100 mg/kg [45 mg/lb], PO, q 12 h) was initiated for PTS management. A 4.7-mg deslorelin implant was injected SC to suppress reproductive behavior. The bird was reexamined for presumed status epilepticus 5 times over 22 months. Seizure episodes coincided with onset of reproductive behavior. The levetiracetam dosage was increased (150 mg/kg [68 mg/lb], PO, q 8 h), and zonisamide (20 mg/kg [9.1 mg/lb], PO, q 12 h) was added to the treatment regimen. Additional deslorelin implants were administered every 2 to 6 months to suppress reproductive behavior. The owner was trained to administer midazolam intranasally or IM as needed at home. The treatment regimen helped control but did not eliminate seizure activity. The bird was euthanized 22 months after PTS diagnosis for reasons unrelated to the TBI or PTS.

CLINICAL RELEVANCE

Long-term management of PTS in a pionus was achieved with levetiracetam and zonisamide administration.

Early Increase in Cortical T2 Relaxation Is a Prognostic Biomarker for the Evolution of Severe Cortical Damage, but Not for Epileptogenesis, after Experimental Traumatic Brain Injury

Prognostic biomarkers for post-injury outcome are necessary for the development of neuroprotective and antiepileptogenic treatments for traumatic brain injury (TBI). We hypothesized that T₂ relaxation magnetic resonance imaging (MRI) predicts the progression of perilesional cortical pathology and epileptogenesis. The EPITARGET animal cohort used for MRI analysis included 120 adult male Sprague-Dawley rats with TBI induced by lateral fluid-percussion injury and 24 sham-operated controls. T₂ MRI was performed at days 2, 7, and 21 post-TBI. The lesioned cortex was outlined, and the T₂ value of each imaging voxel within the lesion area was scored using a five-grade pathology classification. Analysis of 1-month video-electroencephalography recordings initiated 5 months post-TBI indicated that 27% (31 of 114) of the animals with TBI developed epilepsy. Multiple linear regression analysis indicated that T₂-based classification of lesion volume at day 2 and day 7 post-TBI explained the necrotic lesion volume with greatly increased T₂ (>102 ms) at day 21 post-TBI (F_(13,103) = 52.5; p < 0.001; R² =  0.87; adjusted R² = 0.85). The volume of moderately increased (78-102 ms) T₂ at day 7 post-TBI predicted the evolution of large (>12 mm³) cortical lesions (area under the curve, 0.92; p < 0.001; cutoff, 1.9 mm³; false positive rate, 0.10; true positive rate, 0.62). Logistic regression analysis, however, showed that the different severities of T₂ lesion volumes at days 2, 7, and 21 post-TBI did not explain the development of epilepsy (χ²_(18,95) = 18.4; p = 0.427). In addition, the location of the T₂ abnormality within the cortex did not correlate with epileptogenesis. A single measurement of T₂ relaxation MRI in the acute post-TBI phase is useful for identifying post-TBI subjects at highest risk of developing large cortical lesions, and thus, in the greatest need of neuroprotective therapies after TBI, but not the development of post-traumatic epilepsy.

Epilepsy after severe traumatic brain injury: frequency and injury severity

Objective: To estimate national frequency of posttraumatic epilepsy (PTE) after severe traumatic brain injury (TBI) and assess injury severity (Glasgow Coma Scale (GCS) and posttraumatic amnesia (PTA)) as prognostic factors for PTE.

METHODS

Data on patients ≥18 years surviving severe TBI 2004-2016 were retrieved from the Danish Head Trauma Database (n = 1010). The cumulative incidence proportion (CIP) was estimated using death as competing event. The association between injury severity and PTE was assessed using multivariable competing risk regressions.

RESULTS

CIP of PTE 28 days and one year post-TBI was 6.8% (95% confidence interval (CI) 5.4-8.5) and 18.5% (95% CI 16.1-21.1%), respectively. Injury severity was not associated with PTE within 28 days post-TBI but indicated higher PTE-rates in less severely injured patients. PTA-duration >70 days was associated with PTE 29-365 days post-TBI (Adjusted sub-hazard ratio 4.23 (95% CI 1.79-9.99)). GCS was not associated with PTE 29-365 days post-TBI.

CONCLUSION

The PTE frequency was higher compared to previous estimates. Increasing injury severity was associated with PTE 29-365 days post-TBI when measured with PTA, but not with GCS. Though nonsignificant, the increased PTE-risk within 28 days in lower severity suggests an underdiagnosing of PTE.

Epidemiology of traumatic brain injury-associated epilepsy in western China: An analysis of multicenter data

OBJECTIVES

This study aims to explore the probability of developing posttraumatic epilepsy (PTE) in the following 8 years after traumatic brain injury (TBI), the risk factors associated with PTE and its cumulative prevalence.

METHODS

This is a retrospective follow-up study of patients with traumatic brain injury (TBI) discharged from the West China Hospital between January 1, 2011 and December 31, 2017, Chengdu Shang Jin Nan Fu Hospital and Sichuan Provincial People's Hospital from January 1, 2013 to March 1, 2015. We used forward stepwise method to build the final multivariate cox proportional hazard regression model to obtain estimates of hazard ratio (HR) of PTE and 95% confidence intervals (CI). We also conducted Kaplan-Meier survival analysis to investigate the cumulative prevalence of PTE.

RESULTS

The cumulative incidence of PTE rose from 6.2% in one year to 10.6% in eight years. There were more male patients in PTE group and generally older. Besides, patients with PTE tended to have abnormal CT scan results. The risk factors of PTE were male (HR = 1.6, 95% CI: 1.1-2.2, P = 0.009), early posttraumatic seizures (HR = 2.9, 95% CI: 2.2-4.1, P < 0.001), TBI severity (moderate TBI: HR = 3.0, 95% CI: 1.8-5.0, P = 0.001; severe TBI: HR = 4.3, 95% CI: 2.3-7.6, P < 0.029), loss of consciousness (LOC) more than 30 min (30 min-24 h: HR = 1.8, 95% CI: 1.02-3.1, P = 0.041; >24 h: HR = 2.4, 95% CI: 1.4-2.4, P = 0.001), subdural hematoma (SDH) (HR = 1.9, 95% CI: 1.4-2.5, P < 0.001), brain contusion sites (frontal-temporal lobe: HR = 2.7, 95% CI: 1.9-3.9, P < 0.001; other sites: HR = 1.5, 95% CI: 1.01-2.3, P = 0.042) and cranial surgery (HR = 1.7, 95% CI: 1.3-2.3, P < 0.001).

SIGNIFICANCE

The probability of developing PTE increased during the study period. In addition, the risk of developing PTE was significantly associated with gender, EPTS, LOC time, SDH, brain contusion sites, surgery and TBI severity. However, further researches may be needed to predict the risk of PTE in combination with quantitative factors.

Elevated Acute Plasma miR-124-3p Level Relates to Evolution of Larger Cortical Lesion Area after Traumatic Brain Injury

Mechanisms initiated by traumatic brain injury (TBI), leading to the development of progressive secondary injury are poorly understood. MicroRNAs (miRNAs) have a proposed role in orchestrating the post-injury aftermath as a single miRNA can control the expression of several genes. We hypothesized that the post-injury level of circulating brain-enriched miR-124-3p explains the extent of post-TBI cortical lesion. Three separate cohorts of adult male Sprague-Dawley rats (total n = 57) were injured with lateral fluid-percussion-induced TBI. The miR-124-3p levels were measured in whole blood and/or plasma in cohorts 1 and 2 before TBI as well as at 2 d, 7 d, 2 months or 3 months post-TBI. The third cohort (22/57) was imaged with T2-weighted magnetic resonance imaging (MRI) at 2 months post-TBI to quantify cortical lesion area and perilesional T2-enhancement volume. Our data shows that miR-124-3p levels were elevated at 2 d post-TBI in both blood (FC 4.63, p < 0.01) and plasma (FC 1.39, p < 0.05) as compared to controls. Receiver operating curve (ROC) analysis indicated that plasma miR-124-3p level of 34 copies/µl or higher differentiated TBI animals from controls [area under curve (AUC) 0.815, p < 0.05]. The data was validated in the third cohort (FC 1.68, p < 0.05). T2-weighted MRI revealed inter-animal differences in cortical lesion area. Linear regression analysis revealed that higher the plasma miR-124-3p level at 2 d post-TBI, larger the lesion area at chronic time point (R² = 0.327, p < 0.01). Our findings indicate that the extent of lateral fluid-percussion injury-induced chronic cortical pathology associated with the acutely elevated plasma miR-124-3p level.

No prevention or cure of epilepsy as yet

Approximately 20% of all epilepsy is caused by acute acquired injury such as traumatic brain injury, stroke and CNS infection. The known onset of the injury which triggers the epileptogenic process, early presentation to medical care, and a latency between the injury and the development of clinical epilepsy present an opportunity to intervene with treatment to prevent epilepsy. No such treatment exists and yet there has been remarkably little clinical research during the last 20 years to try to develop such treatment. We review possible reasons for this, possible ways to rectify the situations and note some of the ways currently under way to do so. Resective surgical treatment can achieve "cure" in some patients but is sparsely utilized. In certain "self-limiting" syndromes of childhood and adolescence epilepsy remits spontaneously. In a proportion of patients who become seizure free on medications or with dietary treatment, seizure freedom persists when treatment is discontinued. We discuss these situations which can be considered "cures"; and note that at present we have little understanding of mechanism of such cures, and cannot therefore translate them into a treatment paradigm targeting a "cure" of epilepsy. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

A MACHINE LEARNING MODEL TO PREDICT SEIZURE SUSCEPTIBILITY FROM RESTING-STATE FMRI CONNECTIVITY

Traumatic brain injury (TBI) is a leading cause of disability globally. Many patients develop post-traumatic epilepsy, or recurrent seizures following TBI. In recent years, significant efforts have been made to identify biomarkers of epileptogenesis that may assist in preventing seizure occurrence by identifying high-risk patients. We present a novel method of assessing seizure susceptibility using data from 49 patients enrolled in the Epilepsy Bioinformatics Study for Antiepileptogenic Therapy (EpiBioS4Rx). We employ a machine learning paradigm that utilizes a Random Forest classifier trained with resting-state functional magnetic resonance imaging (fMRI) data to predict seizure outcomes. Following 100 rounds of stratified cross-validation with 70% of resting state fMRI scans as the training set and 30% as the testing set, our model was found to assess seizure outcome in the testing set with 69% accuracy. To validate the method, we compared our results with classification by Support Vector Machines and Neural Network classifiers.

Imaging biomarkers of epileptogenecity after traumatic brain injury - Preclinical frontiers

Posttraumatic epilepsy (PTE) is a major neurodegenerative disease accounting for 20% of symptomatic epilepsy cases. A long latent phase offers a potential window for prophylactic treatment strategies to prevent epilepsy onset, provided that the patients at risk can be identified. Some promising imaging biomarker candidates for posttraumatic epileptogenesis have been identified, but more are required to provide the specificity and sensitivity for accurate prediction. Experimental models and preclinical longitudinal, multimodal imaging studies allow follow-up of complex cascade of events initiated by traumatic brain injury, as well as monitoring of treatment effects. Preclinical imaging data from the posttraumatic brain are rich in information, yet examination of their specific relevance to epilepsy is lacking. Accumulating evidence from ongoing preclinical studies in TBI support insight into processes involved in epileptogenesis, e.g. inflammation and changes in functional and structural brain-wide connectivity. These efforts are likely to produce both new biomarkers and treatment targets for PTE.

Use of Diffusional Kurtosis Imaging and Dynamic Contrast-Enhanced MR Imaging to Predict Posttraumatic Epilepsy in Rabbits

BACKGROUND AND PURPOSE

Finding a reliable biomarker to thoroughly assess the brain structure changes in posttraumatic epilepsy is of great importance. Our aim was to explore the value of diffusional kurtosis imaging combined with dynamic contrast-enhanced MR imaging in the evaluation of posttraumatic epilepsy.

MATERIALS AND METHODS

A modified weight-drop device was used to induce traumatic brain injury. Rabbits were exposed to traumatic brain injury or sham injury. Diffusional kurtosis imaging and dynamic contrast-enhanced MR imaging were performed 1 day after injury. Posttraumatic epilepsy was investigated 3 months after injury. The traumatic brain injury group was further divided into 2 groups: the posttraumatic epilepsy and the non-posttraumatic epilepsy groups. Mean kurtosis and volume transfer coefficient values in the cortex, hippocampus, and thalamus were analyzed. After follow-up, the experimental animals were sacrificed for Nissl staining.

RESULTS

The posttraumatic epilepsy group comprised 8 rabbits. In the ipsilateral cortex, the volume transfer coefficient in the traumatic brain injury group was higher than that in the sham group; the volume transfer coefficient in the posttraumatic epilepsy group was higher than that in the non-posttraumatic epilepsy group. In the ipsilateral hippocampus, the volume transfer coefficient in the posttraumatic epilepsy group was higher than that in the non-posttraumatic epilepsy and sham groups. No difference was observed between the non-posttraumatic epilepsy and sham groups. In the ipsilateral cortex, mean kurtosis in the traumatic brain injury group was lower than that in the sham group, and mean kurtosis in the posttraumatic epilepsy group was lower than that in the non-posttraumatic epilepsy group. In the ipsilateral thalamus and hippocampus, mean kurtosis in the traumatic brain injury group was lower than that in the sham group, and mean kurtosis in the posttraumatic epilepsy group was lower than that in the non-posttraumatic epilepsy group. In the contralateral thalamus, mean kurtosis in the traumatic brain injury group was lower than that in the sham group; however, no difference was observed between the posttraumatic epilepsy and non-posttraumatic epilepsy groups.

CONCLUSIONS

Diffusional kurtosis imaging and dynamic contrast-enhanced MR imaging could be used to predict the occurrence of posttraumatic epilepsy in rabbits exposed to experimental traumatic brain injury.

Risk factors for posttraumatic epilepsy: A systematic review and meta-analysis

OBJECTIVE

A systematic review and meta-analysis was performed to identify risk factors for posttraumatic epilepsy (PTE).

METHODS

Two electronic databases (Medline and Embase) were searched to identify studies with a cohort, case-control, or cross-sectional design reporting on epidemiologic evidence regarding risk factors for PTE.

RESULTS

Men had a higher risk of developing PTE than women [relative ratio (RR), 1.32; 95% confidence interval (CI), 1.10-1.59]. A history of alcohol abuse (RR, 2.18; 95% CI, 1.26-3.79), posttraumatic amnesia (RR, 1.31; 95% CI, 1.12-1.53), focal neurologic signs (RR, 1.42; 95% CI, 1.16-1.74), and loss of consciousness at initial traumatic brain injury (TBI) (RR, 1.62; 95% CI, 1.13-2.32) were associated with a greater risk of PTE. TBI-related abnormal neuroimaging findings, including skull fracture (RR, 2.27; 95% CI, 1.49-3.44), midline shift (RR, 1.46; 95% CI, 1.14-1.87), brain contusion (RR, 2.35; 95% CI, 1.69-3.28), subdural hemorrhage (RR, 2.00; 95% CI, 1.33-3.01), and intracranial hemorrhage (RR, 2.65; 95% CI, 1.83-3.82) were strong risk factors for PTE. The risk of developing PTE after skull fracture, mild brain injury, and severe brain injury peaked within the first year after TBI, and then gradually decreased. However, a high risk of PTE was sustained for >10years.

CONCLUSION

The current meta-analysis identified potential risk factors for PTE. The results may contribute to better prevention strategies and treatments for PTE.

Animal models of post-traumatic epilepsy

Post-traumatic epilepsy (PTE) is defined as the development of unprovoked seizures in a delayed fashion after traumatic brain injury (TBI). PTE lies at the intersection of two distinct fields of study, epilepsy and neurotrauma. TBI is associated with a myriad of both focal and diffuse anatomic injuries, and an ideal animal model of epilepsy after TBI must mimic the characteristics of human PTE. The three most commonly used models of TBI are lateral fluid percussion, controlled cortical injury, and weight drop. Much of what is known about PTE has resulted from use of these models. In this review, we describe the most commonly used animal models of TBI with special attention to their advantages and disadvantages with respect to their use as a model of PTE.

The causes of new-onset epilepsy and seizures in the elderly

With increasing age, the prevalence and incidence of epilepsy and seizures increases correspondingly. New-onset epilepsy in elderly people often has underlying etiology, including cerebrovascular diseases, primary neuron degenerative disorders, intracerebral tumors, and traumatic head injury. In addition, an acute symptomatic seizure cannot be called epilepsy, which manifests usually as a common symptom secondary to metabolic or toxicity factors in older people. In this review, we have mainly focused on the causes of new-onset epilepsy and seizures in elderly people. This knowledge will certainly help us to understand the reasons for high incidences of epilepsy and seizures in elderly people. We look forward to controlling epileptic seizures via the treatment of primary diseases in the future.

Epilepsy related to traumatic brain injury

Post-traumatic epilepsy accounts for 10-20% of symptomatic epilepsy in the general population and 5% of all epilepsy. During the last decade, an increasing number of laboratories have investigated the molecular and cellular mechanisms of post-traumatic epileptogenesis in experimental models. However, identification of critical molecular, cellular, and network mechanisms that would be specific for post-traumatic epileptogenesis remains a challenge. Despite of that, 7 of 9 proof-of-concept antiepileptogenesis studies have demonstrated some effect on seizure susceptibility after experimental traumatic brain injury, even though none of them has progressed to clinic. Moreover, there has been some promise that new clinically translatable imaging approaches can identify biomarkers for post-traumatic epileptogenesis. Even though the progress in combating post-traumatic epileptogenesis happens in small steps, recent discoveries kindle hope for identification of treatment strategies to prevent post-traumatic epilepsy in at-risk patients.

Neuroimaging the epileptogenic process

Epilepsy is one of the most common chronic neurological conditions worldwide. Anti-epileptic drugs (AEDs) can suppress seizures, but do not affect the underlying epileptic state, and many epilepsy patients are unable to attain seizure control with AEDs. To cure or prevent epilepsy, disease-modifying interventions that inhibit or reverse the disease process of epileptogenesis must be developed. A major limitation in the development and implementation of such an intervention is the current poor understanding, and the lack of reliable biomarkers, of the epileptogenic process. Neuroimaging represents a non-invasive medical and research tool with the ability to identify early pathophysiological changes involved in epileptogenesis, monitor disease progression, and assess the effectiveness of possible therapies. Here we will provide an overview of studies conducted in animal models and in patients with epilepsy that have utilized various neuroimaging modalities to investigate epileptogenesis.

Posttraumatic Epilepsy: What's Contusion Got to Do With It?

Text of Abstract Liability to develop posttraumatic epilepsy (PTE) correlates in a general way with trauma dose. While contusion of the brain produces an admixture of extravasated blood, edema fluid and necrotic tissue at the site of skull trauma and in regions remote from the direct force, an unpredictable cascade of shearing injury, torsion and rotation and a myriad of physiological changes occur in structures subject to the mechanical pressure wave. Animal models mimic components of injury, some more thoroughly than others. Designing a treatment that is a prophylaxis for the development of PTE awaits understanding the mechanisms of epileptogenesis initiated by trauma.

A Rehabilomics focused perspective on molecular mechanisms underlying neurological injury, complications, and recovery after severe TBI

The molecular mechanisms underlying TBI pathophysiology and recovery are both complex and varied. Further, the pathology underlying many of the clinical sequelae observed in this population evolve over the acute injury period and encompass the subacute and chronic phases of recovery, supporting the contemporary concept that TBI is a chronic disease rather than a static insult from which limited recovery occurs. TBI related complications can also span from acute care to the very chronic stages of recovery that occur years after the initial trauma. Despite ongoing neurodegeneration, the TBI recovery period is also characterized by a propensity for neuroplasticity and rewiring through multiple mechanisms. This review summarizes key elements of acute pathophysiology, how they link to structural damage and ongoing degeneration, and how this process coincides with a permissive neuroplastic environment. The pathophysiology of selected TBI related complications is also discussed. Each of these concepts is studied through the lens of Rehabilomics, wherein an emphasis is placed on biomarker studies characterizing these pathophysiological mechanisms, and biomarker profiles are assessed in relation to multi-modal outcomes and susceptibility to rehabilitation relevant complications. In reviewing these concepts, implications for future research and theranostic principles for patient care are presented.

Seizures: emergency neuroimaging

The various findings observed on computed tomography (CT) and magnetic resonance (MR) imaging examinations in patients with seizures reflect the variety of different causes that give rise to this common neurologic symptom. In the emergency setting, CT is most valuable in its ability to accurately identify acute abnormalities that require emergent medical or surgical treatment. MR imaging, by contrast, is usually reserved for patients with recurrent or refractory seizures. The accurate interpretation of either modality requires familiarity with how seizures are classified clinically, the most common presenting features of different causes for seizures, the relevant neuroanatomy, and the imaging manifestations of both common and uncommon causes of seizures and epilepsy. Of particular practical importance to the radiologist is the ability to recognize (1) the most common findings in patients with recurrent seizures and (2) potentially reversible causes for seizures that require prompt intervention to avoid or minimize permanent brain injury. This article surveys a variety of different causes for seizures and epilepsy, focusing on specific clinical features that can help to refine differential diagnosis, and on imaging findings characteristic of different disorders.

Chronic dysfunction of astrocytic inwardly rectifying K+ channels specific to the neocortical epileptic focus after fluid percussion injury in the rat

Astrocytic inwardly rectifying K(+) currents (I(KIR)) have an important role in extracellular K(+) homeostasis, which influences neuronal excitability, and serum extravasation has been linked to impaired K(IR)-mediated K(+) buffering and chronic hyperexcitability. Head injury induces acute impairment in astroglial membrane I(KIR) and impaired K(+) buffering in the rat hippocampus, but chronic spontaneous seizures appear in the perilesional neocortex--not the hippocampus--in the early weeks to months after injury. Thus we examined astrocytic K(IR) channel pathophysiology in both neocortex and hippocampus after rostral parasaggital fluid percussion injury (rpFPI). rpFPI induced greater acute serum extravasation and metabolic impairment in the perilesional neocortex than in the underlying hippocampus, and in situ whole cell recordings showed a greater acute loss of astrocytic I(KIR) in neocortex than hippocampus. I(KIR) loss persisted through 1 mo after injury only in the neocortical epileptic focus, but fully recovered in the hippocampus that did not generate chronic seizures. Neocortical cell-attached recordings showed no loss or an increase of I(KIR) in astrocytic somata. Confocal imaging showed depletion of KIR4.1 immunoreactivity especially in processes--not somata--of neocortical astrocytes, whereas hippocampal astrocytes appeared normal. In naïve animals, intracortical infusion of serum, devoid of coagulation-mediating thrombin activity, reproduces the effects of rpFPI both in vivo and at the cellular level. In vivo serum infusion induces partial seizures similar to those induced by rpFPI, whereas bath-applied serum, but not dialyzed albumin, rapidly silenced astrocytic K(IR) membrane currents in whole cell and cell-attached patch-clamp recordings in situ. Thus both acute impairment in astrocytic I(KIR) and chronic spontaneous seizures typical of rpFPI are reproduced by serum extravasation, whereas the chronic impairment in astroglial I(KIR) is specific to the neocortex that develops the epileptic focus.

Post-traumatic epilepsy: an overview

Post-traumatic seizures (PTS) and post-traumatic epilepsy (PTE) are complications from traumatic brain injury (TBI). PTE refers to recurrent and unprovoked PTS that occur at least 1 week after TBI. Seizures during the first week after TBI are considered provoked, an acute complication from head injury, while seizures occurring 1 week after TBI are considered a manifestation of PTE and if only a single seizure occurs it is known as late PTS. EEG and neuroimaging help in the diagnosis of PTE. Predictors for PTE include TBI severity, presence of intracranial bleeding and early PTS. Several clinical trials have demonstrated that antiepileptic drugs are effective in reducing the frequency of acute PTS, but do not appear to alter the natural history of late PTS or PTE.

Current themes in neuroimaging of epilepsy: brain networks, dynamic phenomena, and clinical relevance

Brain scanning methods were first applied in patients with epilepsy more than 30years ago. A very substantial literature now exists in this field, which is exponentially increasing. Contemporary neuroimaging studies in epilepsy reflect new concepts in the epilepsies, as well as current methodological developments. In particular, this area is emphasising the role of networks in epileptogenicity, the existence of dynamic phenomena which can be captured by imaging, and is beginning to validate the implementation of neuroimaging in the clinic. Here, recent studies of the last 5years are reviewed, covering the full range of neuroimaging methods with SPECT, PET and MRI in epilepsy.

Loss of astrocytic domain organization in the epileptic brain

Gliosis is a pathological hallmark of posttraumatic epileptic foci, but little is known about these reactive astrocytes beyond their high glial fibrillary acidic protein (GFAP) expression. Using diolistic labeling, we show that cortical astrocytes lost their nonoverlapping domain organization in three mouse models of epilepsy: posttraumatic injury, genetic susceptibility, and systemic kainate exposure. Neighboring astrocytes in epileptic mice showed a 10-fold increase in overlap of processes. Concurrently, spine density was increased on dendrites of excitatory neurons. Suppression of seizures by the common antiepileptic, valproate, reduced the overlap of astrocytic processes. Astrocytic domain organization was also preserved in APP transgenic mice expressing a mutant variant of human amyloid precursor protein despite a marked upregulation of GFAP. Our data suggest that loss of astrocytic domains was not universally associated with gliosis, but restricted to seizure pathologies. Reorganization of astrocytes may, in concert with dendritic sprouting and new synapse formation, form the structural basis for recurrent excitation in the epileptic brain.

Uncommon epiloptogenic lesions affecting the temporal lobe

There are several processes implicated as uncommon causes of temporal lobe epilepsy. Trauma is the leading cause of epilepsy in young adults, intracerebral blood collection being the most consistent risk factor of seizures, especially subdural hematomas and brain contusions. Infarction is the entity most commonly related to epilepsy in the elderly population. Seizures usually present as complex seizures with high recurrence between 6 months and 2 years after stroke. There are some radiological characteristics of the affectation associated with high risk of early and late seizures. Noninfectious limbic encephalitis is a syndrome characterized by seizures, memory loss, and confusion. It includes paraneoplasic and non-paraneoplasic limbic encephalitis, both presenting as hyperintense lesion affecting temporobasal regions more evident with fluid-attenuated inversion recovery sequences. Paraneoplasic limbic encephalitis is associated with several types of tumor-induced autoimmunity against the nervous system. The tumors most frequently implicated are the lungs, testis, and breast, including Hodgkin's lymphoma, teratoma, and thymoma in young patients. Once a tumor is excluded, non-paraneoplasic limbic encephalitis has to be considered by investigating the presence of antibodies against voltage-gated potassium channels. It is associated with hyponatremia and responds to regimens of steroids, plasma exchange, and intravenous immunoglobulins. Finally, herpetic limbic encephalitis is also associated with seizures, accompanied by fever and neurologic symptoms. It presents characteristic findings and distribution on magnetic resonance imaging, which shows abnormalities in more than 90% of patients with proven Herpes simplex virus type 1.

Time interval from a brain insult to the onset of infantile spasms

The temporal latency between an encephalopathic event and the onset of infantile spasms cannot be determined in the majority of symptomatic cases (e.g. genetic conditions, cerebral malformations). However, we can measure this interval when a previously normal infant sustains brain injury followed by infantile spasms. This information has implications for understanding the underlying pathophysiologic basis for infantile spasms and, also, is germane to allegations that a close temporal relationship between vaccination and the onset of this seizure disorder establishes causation. We identified 19 published cases with sufficient information. The interval between brain injury and the onset of infantile spasms ranged from 6 weeks to 11 months (mean = 5.1 months). A similar temporal latency occurs in children with perinatal cerebral infarction and infantile spasms. We conclude that infantile spasms do not occur acutely following an encephalopathic event. This interval of weeks to months is consistent with prior studies indicating temporal latency between brain injury and the onset of other types of epilepsy, as well as with the previously proposed developmental desynchronization hypothesis. The findings refute claims that a close temporal association between an immunization and the onset of infantile spasms establishes causation.

Prevention and treatment of post-traumatic epilepsy

Post-traumatic epilepsy is reported after 2-5% of closed head injuries but up to 50% or more following penetrating head injury. Despite several studies, no drug strategy has been able, to date, to quench the biochemical events leading to epileptogenesis. One possibility is that treatment with available antiepileptic drugs has been implemented too late, and thus, ultra-early treatment might still be able to stop the neurochemical epileptogenic cascade dead in its tracks. However, currently drug therapy should be instituted only after the first late unprovoked seizure.