Seizures, epilepsy, and functional recovery after traumatic brain injury: a reappraisal

Seizures in Children With Severe Traumatic Brain Injury

OBJECTIVE

Traumatic brain injury causes substantial morbidity and mortality in children. Posttraumatic seizures may worsen outcomes after traumatic brain injury. Posttraumatic seizures risk factors are not completely understood. Our objective was to clarify posttraumatic seizures risk factors in a large cohort of children with severe traumatic brain injury.

DESIGN

Retrospective cohort study of a probabilistically linked dataset from the National Trauma Data Bank and the Pediatric Health Information Systems database, 2007-2010.

SETTING

Twenty-nine U.S. children's hospitals.

PATIENTS

A total of 2,122 children (age, < 18 yr old at admission) with linked National Trauma Data Bank and Pediatric Health Information Systems records, severe (emergency department Glasgow Coma Scale, < 8) traumatic brain injury, hospital length of stay more than 24 hours, and nonmissing disposition.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The outcome was posttraumatic seizures, identified using validated International Classification of Diseases, 9th Revision, Clinical Modification diagnosis codes. Prespecified candidate predictors of posttraumatic seizures included age, injury mechanism, emergency department Glasgow Coma Scale, intracranial hemorrhage type, hypoxia, hypotension, and cardiac arrest. Posttraumatic seizures were diagnosed in 25.2% of children with severe traumatic brain injury. In those without abuse/assault or subdural hemorrhage, the posttraumatic seizures rate varied between 36.6% in those less than 2 years old and 16.4% in those 14-17 years old. Age, abusive mechanism, and subdural hemorrhage are each significant predictors of posttraumatic seizures. The risk of posttraumatic seizures has a complex relationship with these predictors. The estimated odds of posttraumatic seizures decrease with advancing age, odds ratio equal to 0.929 (0.905-0.954) per additional year of age with no abuse/assault and no subdural hemorrhage; odds ratio equal to 0.820 (0.730-0.922) per additional year of age when abuse and subdural hemorrhage are present. An infant with accidental traumatic brain injury and subdural hemorrhage has approximately the same estimated probability of posttraumatic seizures as an abused infant without subdural hemorrhage (47% [95% CI, 39-55%] vs 50% [95% CI, 41-58%]; p = 0.69). The triad of young age, injury by abuse/assault, and subdural hemorrhage confers the greatest estimated probability for posttraumatic seizures (60% [95% CI, 53-66%]).

CONCLUSIONS

Posttraumatic seizures risk in children with severe traumatic brain injury is greatest with a triad of younger age, injury by abuse/assault, and subdural hemorrhage. However, posttraumatic seizures are common even in the absence of these factors.

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.

Post-Traumatic Neural Depression and Neurobehavioral Recovery after Brain Injury

There are an estimated 2 million traumatic brain injuries (TBIs) each year in the United States, making the yearly incidence eight times greater than that of breast cancer and 34 times greater than HIV/AIDS. Still, it remains a "silent epidemic" because TBI results in persistent neurobehavioral impairment, without necessarily imparting a physical scar. The present review is a comparative analysis of TBI research, both basic and applied, outlining the evidence that at least one component of the brain's innate response to insult (e.g., post-traumatic neural depression) is sufficiently well understood to be the target of additional clinical studies and therapeutic strategy development.

Seizure heralding functional recovery in a patient with apallic syndrome: A case report with retrospective-prospective observation

BACKGROUND

It has been suggested that there exists a close relationship between seizure discharges and functional recovery from brain injury, and that paroxysmal bombardment in late seizures may herald functional recovery or may "kick-start" recovery.

CASE REPORT

We report the case of a 52-year-old patient who, following a subarachnoid hemorrhage and multiple surgeries, experienced discernible apallic syndrome of long duration. His hospitalization is well documented. The patient underwent protracted, intense rehabilitation, but he remained in this prolonged state of loss of consciousness and behavioral passivity until he experienced a series of periodic seizures. Widespread improvement in his cognitive and functional abilities coincided closely with the seizure activity. The literature on this topic is reviewed.

CONCLUSION

This case confirms the close relationship between seizure discharges and functional recovery reported in preclinical literature.

Electrical stimulation of the vagus nerve enhances cognitive and motor recovery following moderate fluid percussion injury in the rat

Intermittent, chronically delivered electrical stimulation of the vagus nerve (VNS) is an FDA-approved procedure for the treatment of refractory complex/partial epilepsy in humans. Stimulation of the vagus has also been shown to enhance memory storage processes in laboratory rats and human subjects. Recent evidence suggests that some of these effects of VNS may be due to the activation of neurons in the nucleus locus coeruleus resulting in the release of norepinephrine (NE) throughout the neuraxis. Because antagonism of NE systems has been shown to delay recovery of function following brain damage, it is possible that enhanced release of NE in the CNS may facilitate recovery of function. To evaluate this hypothesis the lateral fluid percussion injury (LFP) model of traumatic brain injury was used and a variety of motor and cognitive behavioral tests were employed to assess recovery in pre-trained stimulated, control, and sham-injured laboratory rats. Two hours following moderate LFP, vagus nerve stimulation (30.0-sec trains of 0.5 mA, 20.0 Hz, biphasic pulses) was initiated. Stimulation continued in each animal's home cage at 30-min intervals for a period of 14 days, with the exception of brief periods when the animals were disconnected for behavioral assessments. Motor behaviors were evaluated every other day following LFP and tests included beam walk, locomotor placing, and skilled forelimb reaching. In each measure an enhanced rate of recovery and /or level of final performance was observed in the VNS-LFP animals compared to nonstimulated LFP controls. Behavior in the Morris water maze was assessed on days 11-14 following injury. Stimulated LFP animals showed significantly shorter latencies to find the hidden platform than did controls. Despite these behavioral effects, neurohistological examination did not reveal significant differences in lesion extent, density of fluorojade positive neurons, reactive astrocytes or numbers of spared neurons in the CA3 subarea of the hippocampus, at least at the one time point studied 15 days post-injury. These results support the idea that vagus nerve stimulation enhances the neural plasticity that underlies recovery of function following brain damage and provides indirect support for the hypothesis that enhanced NE release may mediate the effect. Importantly, since VNS facilitated both the rate of recovery and the extent of motor and cognitive recovery, these findings suggest that electrical stimulation of the vagus nerve may prove to be an effective non-pharmacological treatment for traumatic brain injury.

Diffusion tensor imaging in late posttraumatic epilepsy

PURPOSE

The main objective of this study was to use diffusion tensor imaging (DTI) to search and quantify the extent of abnormality beyond the obvious lesions seen on the T2 and fluid-attenuation inversion recovery (FLAIR) magnetic resonance images in patients with chronic traumatic brain injury (TBI) with and without epilepsy.

METHODS

DTI was performed on 23 chronic TBI patients (with late posttraumatic epilepsy, n=14; without epilepsy, n=9) and 11 age-matched controls. The ratios of fractional anisotropy (FA) and mean diffusivity (MD) between the regions of interest beyond the T2/FLAIR-visualized abnormality and the corresponding contralateral normal-appearing region were calculated. FA and MD ratios were compared for relative changes in these parameters among the TBI subjects with and without epilepsy and controls. Tissue volumes exhibiting abnormalities on DTI also were measured in these patients.

RESULTS

The mean regional FA ratio was significantly lower, whereas the mean regional MD value was higher in patients with TBI compared with controls. The mean regional FA ratio was significantly lower in TBI patients with epilepsy (0.57+/-0.059) than in those without epilepsy (0.68+/-0.039). Although the regional MD ratio was higher in TBI patients with epilepsy (1.15+/-0.140) relative to those without epilepsy (1.09+/-0.141), the difference did not reach statistical significance. The tissue volume with low FA value also was found to be higher in TBI patients with epilepsy than without.

CONCLUSIONS

Severity of injury as predicted by the DTI-derived increased volume of microstructure damage is associated with delayed posttraumatic epilepsy in TBI patients. These findings could be valuable in predicting epileptogenesis in patients with chronic TBI.

Cortical injury affects short-term plasticity of evoked excitatory synaptic currents

The hypothesis that plastic changes in the efficacy of excitatory neurotransmission occur in areas of chronic cortical injury was tested by assessing short-term plasticity of evoked excitatory synaptic currents (EPSCs) in neurons of partially isolated neocortical islands (undercut cortex). Whole cell recordings were obtained from layer V pyramidal neurons of sensorimotor cortical slices prepared from P36-P43 control and undercut rats. AMPA/kainate receptor-mediated EPSCs elicited by stimuli delivered at 40 to 66.7 Hz exhibited more paired-pulse depression (PPD) in undercut cortex than control, the time constant of depression evoked by trains of 20- to 66.7-Hz stimuli was faster, and the steady-state amplitude of EPSCs reached after five to seven EPSCs was lower. An antagonist of the glutamate autoreceptor, group II mGluR, increased the steady-state amplitude of EPSCs from undercut but not control cortex, suggesting that activation of presynaptic receptors by released glutamate is more prominent in undercut cortex. In contrast, the GABA(B) receptor antagonist (2S)-3-[[(1S)-1-(3,4-dichlorophenyl)ethyl]amino-2-hydroxypropyl](phenylmethyl)phosphinic acid had no effect. Increasing [Ca(2+)](o) from 2 to 4 mM increased PPD, with a smaller effect in neurons of the undercut. The I-V relationship of AMPA/kainate receptor-mediated EPSCs was close to linear in both control and undercut neurons, and spermine had no significant effect on the EPSCs, suggesting that decreases in postsynaptic glutamate receptors containing the GluR2 subunit were not involved in the alterations in short-term plasticity. Results are compatible with an increase in the probability of transmitter release at excitatory synapses in undercut cortex due to functional changes in presynaptic terminals.

Differential Effects of the Anticonvulsant Topiramate on Neurobehavioral and Histological Outcomes following Traumatic Brain Injury in Rats

The efficacy of topiramate, a novel therapeutic agent approved for the treatment of seizure disorders, was evaluated in a model of traumatic brain injury (TBI). Adult male rats were anesthetized (sodium pentobarbital, 60 mg/kg, i.p.), subjected to lateral fluid percussion brain injury (n = 60) or sham injury (n = 47) and randomized to receive either topiramate or vehicle at 30 min (30 mg/kg, i.p.), and 8, 20 and 32 h postinjury (30 mg/kg, p.o.). In Study A, memory was evaluated using a Morris water maze at 48 h postinjury, after which brain tissue was evaluated for regional cerebral edema. In Study B, animals were evaluated for motor function at 48 h and 1, 2, 3, and 4 weeks postinjury using a composite neuroscore and the rotating pole test and for learning ability at 4 weeks. Brains were analyzed for hemispheric tissue loss and hippocampal CA3 cell loss. Topiramate had no effect on posttraumatic cerebral edema or histologic damage when compared to vehicle. At 48 h, topiramate treatment improved memory function in sham but not brain-injured animals, while at one month postinjury it impaired learning performance in brain-injured but not sham animals. Topiramate significantly improved composite neuroscores at 4 weeks postinjury and rotating pole performance at 1 and 4 weeks postinjury, suggesting a potentially beneficial effect on motor function following TBI.

Posttraumatic epilepsy: neuroradiologic and neuropsychological assessment of long-term outcome

PURPOSE

We sought to detect the incidence and the risk factors of posttraumatic epilepsy (PTE) in rehabilitation patients; to define the influence of PTE for late clinical and functional outcome; and to assess the cognitive and behavioral features of the patients with PTE.

METHODS

Patients were examined with (a) cognitive and behavioral examinations, which included a clinical interview and psychometric tests performed by an expert clinical psychologist; (b) single-photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI); and (c) functional evaluation including the Glasgow Outcome Scale (GOS) and the Functional Independence Measure (FIM).

RESULTS

Of the 143 patients examined in this study, in 27 (19%), seizures developed after a mean time from trauma of 11.9 +/- 8.6 months. The occurrence of PTE was significantly correlated with the hypoperfusion in temporal lobes (p < 0.004), the degree of hydrocephalus (p < 0.04), the evidence of intracerebral hematoma (p < 0.01), and operative brain injury (p < 0.001). Patients with epilepsy showed a significantly higher incidence of personality disorders than did patients without epilepsy. The uninhibited behavior, irritability, and agitated and aggressive behavior were significantly more frequent and severe in PTE patients. The psychometric tests intended to explore memory, language, intelligence, attention, and spatial cognition did not show any significant difference between those with and without epilepsy. PTE also was significantly correlated with a worse functional outcome 1 year after the trauma.

CONCLUSIONS

The degrees of hydrocephalus and of hypoperfusion in the temporal lobes are significant risk factors for late PTE. Another main finding of our study is the absence of influence of epilepsy on cognitive disorders; its influence on neurobehavioral disorders and functional outcome is discussed.

The effects of repeated minimal electroconvulsive shock exposure on levels of mRNA encoding fibroblast growth factor-2 and nerve growth factor in limbic regions

Chronic, but not acute, exposure to minimal electroconvulsive shock (ECS) has been shown to decrease vulnerability to neuronal cell death, without itself causing neuronal damage. One potential mechanism for the neuroprotective effect of ECS is the increase in fibroblast growth factor-2 (FGF-2) which occurs after chronic, but not acute, ECS exposure. This raises the possibility that repeated seizures over a period of several days may alter the transcriptional regulation of FGF-2. To test this hypothesis, the present study compared the effect of acute (1 day) vs. chronic (7 days) ECS treatment on levels of mRNA for FGF-2 in rhinal and frontal cortices, hippocampus, and olfactory bulbs. In addition, mRNA for another prominent neurotrophic factor, nerve growth factor (NGF), was assayed concurrently. At 8 h after acute ECS, mRNA levels increased by 60% for FGF-2 and 136% for NGF in rhinal cortex, 32% for FGF-2 and 36% for NGF in frontal cortex, and by 13% for NGF in hippocampus. After 7 days of ECS treatment the respective increases were 72% and 80%, 53% and 38%, and 28%. No increases were observed in olfactory bulbs after either treatment regimen. The peak increases in FGF-2 mRNA were consistently greater after chronic treatment, but the differences from those seen acutely reached significance in frontal cortex only. However, the duration over which mRNA for FGF-2 was elevated did not differ between the acute and chronic ECS groups. NGF mRNA induction was neither enhanced nor prolonged as a result of chronic ECS as compared to acute ECS treatment. These results suggest that chronic ECS treatment may lead to an enhanced rate of transcription of message for FGF-2 but not for NGF, in selected brain regions. At the same time, the results indicate that chronic ECS treatment induces FGF-2 and NGF mRNA expression in a tissue-specific manner and that this induction is maintained over the 7-day treatment period. The sustained increases in mRNAs for these trophic factors may contribute to the neuroprotective actions of chronic ECS treatment.

Vigabatrin directed against kindled seizures following cortical insult: impact on epileptogenesis and somatosensory recovery

The anticonvulsant drug vigabatrin has not been found to be detrimental to the recovery process when administered following focal cortical insult. This finding is in contrast to the negative postinjury consequences of other anticonvulsant drugs (e.g., phenobarbital and diazepam) with more direct activation of the GABA/benzodiazepine receptor complex. Moreover, phenobarbital directed against kindled seizures affects functional recovery more adversely than either the drug or subconvulsive seizures alone. The purpose of the present study was to determine whether vigabatrin (150, 200, and 250 mg/kg) directed against kindled seizures would impact recovery from lesion-induced somatosensory deficits. Vigabatrin was coupled with daily electrical kindling of the amygdala during the first week after a unilateral anteromedial cortex (AMC) lesion. Somatosensory recovery was assessed using bilateral tactile stimulation tests. Animals receiving the highest dose of vigabatrin prior to electrical kindling (250 mg/kg vigabatrin/kindled) remained significantly impaired even after two months of testing relative to vehicle/kindled, kindled/250 mg/kg vigabatrin, which received vigabatrin after electrical kindling, and the 150, 200, and 250 mg/kg vigabatrin/nonkindled groups (p < 0.0001). In contrast, neither vigabatrin (at any of the doses tested) nor subconvulsive kindled seizures impacted the recovery process (p > 0.05) when administered alone (i.e., without the drug + seizure interaction). These data add to the accumulating experimental and clinical evidence suggesting that the neurobehavioral consequences of the interaction between anticonvulsant drugs and subclinical seizures after brain insult are detrimental to functional recovery.

Pharmacological prophylaxis of post-traumatic epilepsy

Early and late epileptic seizures are a frequent complication of severe head traumas. The administration of anticonvulsant drugs immediately after head injury is commonly implemented as a prophylactic measure; however, there is a lack of consensus on the usefulness of prophylaxis with anticonvulsants for the prevention of late post-traumatic epilepsy (PTE). The inconsistent evidence accumulated so far from clinical studies, most nonrandomised and uncontrolled in design, and the limited knowledge of the processes underlying post-traumatic epileptogenesis, do not warrant empirical pharmacological prophylaxis with long term administration of conventional anticonvulsants. Phenytoin and phenobarbital (phenobarbitone) are used to a large extent in this indication. As a general rule, a benefit/risk analysis in individual patients should drive prophylactic drug prescription in PTE as it can have potential detrimental effects on a patient's recovery. New compounds, such as free-radical scavengers and antiperoxidants, show encouraging experimental results, but their clinical use is still very limited.

Phenobarbital administration directed against kindled seizures delays functional recovery following brain insult

Anti-convulsant drug administration or recurrent seizures can impact functional recovery following brain insult. The nature of that impact depends on a variety of factors, including timing of drug administration and drug mechanism of action, as well as seizure number, timing, and severity. The objective of this study was to determine the functional consequences of anti-convulsant administration directed against seizure activity in brain-damaged animals. To this end, phenobarbital was coupled with daily electrical kindling of the amygdala beginning 48 h after a unilateral anteromedial cortex lesion. Recovery from somatosensory deficits was assessed, as was regional atrophy and basic fibroblast growth factor (bFGF) expression. Animals receiving phenobarbital prior to daily kindling failed to recover within 2 months of testing. In contrast, animals receiving saline prior to kindling as well as phenobarbital-treated non-kindled animals recovered within 2 months after the lesion. Though the exact mechanisms underlying these behavioral phenomena remain uncertain, patterns of bFGF expression among the groups provide some insight. Taken together, results from the present study suggest that anti-convulsant drug administration directed against subclinical seizure activity can be more detrimental to functional recovery than seizures alone or anti-convulsant drug treatment after seizure activity has occurred.

A new model of chronic temporal lobe epilepsy induced by electrical stimulation of the amygdala in rat

Spontaneous seizures are the hallmark of human epilepsy but they do not occur in most of the epilepsy models that are used to investigate the mechanisms of epilepsy or to test new antiepileptic compounds. This study was designed to develop a new focal epilepsy model that mimics different aspects of human temporal lobe epilepsy (TLE), including the occurrence of spontaneous seizures. Self-sustained status epilepticus (SSSE) lasting for 6-20 h was induced by a 20-30 min stimulation of the lateral nucleus of the amygdala (100 ms train of 1 ms, 60 Hz bipolar pulses, 400 microA, every 0.5 s). Stimulated rats (n = 16) were monitored with a video-EEG recording system every other day (24 h/day) for 6 months, and every other video-EEG recording was analyzed. Spontaneous epileptic seizures (total number 3698) were detected in 13 of the 15 animals (88%) after a latency period of 6 to 85 days (median 33 days). Four animals (31%) had frequent (697-1317) seizures and 9 animals (69%) had occasional seizures (1-107) during the 6-months follow-up period. Fifty-seven percent of the seizures occurred during daytime (lights on 07:00-19:00 h). At the end of the follow-up period, epileptic animals demonstrated impaired spatial memory in the Morris water-maze. Histologic analysis indicated neuronal loss in the amygdala, hippocampus, and surrounding cortical areas, and mossy fiber sprouting in the dentate gyrus. The present data indicate that focal stimulation of the amygdala initiates a cascade of events that lead to the development of spontaneous seizures in rats. This model provides a new tool to better mimic different aspects of human TLE for investigation of the pathogenesis of TLE or the effects of new antiepileptic compounds on status epilepticus, epileptogenesis, and spontaneous seizures.

Tetrodotoxin prevents posttraumatic epileptogenesis in rats

Severe cortical trauma frequently causes epilepsy that develops after a long latency. We hypothesized that plastic changes in excitability during this latent period might be initiated or sustained by the level of neuronal activity in the injured cortex. We therefore studied effects of action potential blockade by application of tetrodotoxin (TTX) to areas of cortical injury in a model of chronic epileptogenesis. Partially isolated islands of sensorimotor cortex were made in 28- to 30-day-old male Sprague-Dawley rats and thin sheets of Elvax polymer containing TTX or control vehicle were implanted over lesions. Ten to 15 days later neocortical slices were obtained through isolates for electrophysiological studies. Slices from all animals (n = 12) with lesions contacted by control-Elvax (58% of 36 slices) exhibited evoked epileptiform field potentials, and those from 4 rats had spontaneous epileptiform events. Only 2 of 11 lesioned animals and 6% of slices from cortex exposed to TTX in vivo exhibited evoked epileptiform potentials, and no spontaneous epileptiform events were observed. There was no evidence of residual TTX during recordings. TTX-Elvax was ineffective in reversing epileptogenesis when implanted 11 days after cortical injury. These data suggest that development of antiepileptogenic drugs for humans may be possible.