Do prolonged febrile seizures produce medial temporal sclerosis? Hypotheses, MRI evidence and unanswered questions

Focality in Febrile Seizures: A Retrospective Assessment Using Arterial Spin Labeling MRI

PURPOSE

 Defining focality of febrile seizures (FS) in clinical practice remains controversial. We investigated focality issues in FS with a postictal arterial spin labeling (ASL) sequence.

METHODS

 We retrospectively reviewed 77 children (median: 19.0 months, range: 15.0-33.0 months) who consecutively visited our emergency room for FS and underwent brain magnetic resonance imaging (MRI), including the ASL sequence, within 24 hours of seizure onset. ASL data were visually analyzed to assess perfusion changes. Factors related to the perfusion changes were investigated.

RESULTS

 The mean time to ASL acquisition was 7.0 (interquartile range: 4.0-11.0) hours. The most common seizure classification was unknown-onset seizures (n = 37, 48%), followed by focal-onset (n = 26, 34%) and generalized-onset seizures (n = 14, 18%). Perfusion changes were observed in 43 (57%) patients: most were hypoperfusion (n = 35, 83%). The temporal regions were the most common location of perfusion changes (n = 26, 60%); the majority of these were distributed in the unilateral hemisphere. Perfusion changes were independently associated with seizure classification (focal-onset seizures, adjusted odds ratio [aOR]: 9.6, p = 0.01; unknown-onset seizures aOR: 10.4, p < 0.01), and prolonged seizures (aOR: 3.1, p = 0.04), but not with other factors (age, sex, time to MRI acquisition, previous FS, repeated FS within 24 hour, family history of FS, structural abnormality on MRI, and developmental delay). The focality scale of seizure semiology positively correlated with perfusion changes (R = 0.334, p < 0.01).

CONCLUSION

 Focality in FS may be common, and its primary origin might be the temporal regions. ASL can be useful for assessing focality in FS, particularly when seizure onset is unknown.

Quantitative Evaluation of Medial Temporal Lobe Morphology in Children with Febrile Status Epilepticus: Results of the FEBSTAT Study

BACKGROUND AND PURPOSE

The pathogenesis of febrile status epilepticus is poorly understood, but prior studies have suggested an association with temporal lobe abnormalities, including hippocampal malrotation. We used a quantitative morphometric method to assess the association between temporal lobe morphology and febrile status epilepticus.

MATERIALS AND METHODS

Brain MR imaging was performed in children presenting with febrile status epilepticus and control subjects as part of the Consequences of Prolonged Febrile Seizures in Childhood study. Medial temporal lobe morphologic parameters were measured manually, including the distance of the hippocampus from the midline, hippocampal height:width ratio, hippocampal angle, collateral sulcus angle, and width of the temporal horn.

RESULTS

Temporal lobe morphologic parameters were correlated with the presence of visual hippocampal malrotation; the strongest association was with left temporal horn width (P < .001; adjusted OR, 10.59). Multiple morphologic parameters correlated with febrile status epilepticus, encompassing both the right and left sides. This association was statistically strongest in the right temporal lobe, whereas hippocampal malrotation was almost exclusively left-sided in this cohort. The association between temporal lobe measurements and febrile status epilepticus persisted when the analysis was restricted to cases with visually normal imaging findings without hippocampal malrotation or other visually apparent abnormalities.

CONCLUSIONS

Several component morphologic features of hippocampal malrotation are independently associated with febrile status epilepticus, even when complete hippocampal malrotation is absent. Unexpectedly, this association predominantly involves the right temporal lobe. These findings suggest that a spectrum of bilateral temporal lobe anomalies are associated with febrile status epilepticus in children. Hippocampal malrotation may represent a visually apparent subset of this spectrum.

Risk factors for subsequent febrile seizures in the FEBSTAT study

OBJECTIVES

To identify risk and risk factors for developing a subsequent febrile seizure (FS) in children with a first febrile status epilepticus (FSE) compared to a first simple febrile seizure (SFS). To identify home use of rescue medications for subsequent FS.

METHODS

Cases included a first FS that was FSE drawn from FEBSTAT and Columbia cohorts. Controls were a first SFS. Cases and controls were classified according to established FEBSTAT protocols. Cumulative risk for subsequent FS over a 5-year period was compared in FSE versus SFS, and Cox proportional hazards regression was conducted. Separate analysis examined subsequent FS within FSE. The use of rescue medications at home was assessed for subsequent FS.

RESULTS

Risk for a subsequent FSE was significantly increased in FSE versus SFS. Any magnetic resonance imaging (MRI) abnormality increased the risk 3.4-fold (p < 0.05), adjusting for age at first FS and FSE and in analyses restricted to children whose first FS was FSE (any MRI abnormality hazard ratio [HR] 2.9, p < 0.05). The risk for a second FS of any type or of subsequent FS lasting >10 min over the 5-year follow-up did not differ in FSE versus SFS. Rectal diazepam was administered at home to 5 (23.8%) of 21 children with subsequent FS lasting ≥10 min.

SIGNIFICANCE

Compared to controls, FSE was associated with an increased risk for subsequent FSE, suggesting the propensity of children with an initial prolonged seizure to experience a prolonged recurrence. Any baseline MRI abnormality increased the recurrence risk when FSE was compared to SFS and when FSE was studied alone. A minority of children with a subsequent FS lasting 10 min or longer were treated with rectal diazepam at home, despite receiving prescriptions after the first FSE. This indicates the need to further improve the education of clinicians and parents in order to prevent subsequent FSE.

Hippocampal Malrotation Is Associated With Prolonged Febrile Seizures: Results of the FEBSTAT Study

OBJECTIVE

Hippocampal malrotation is characterized by incomplete hippocampal inversion with a rounded shape and blurred internal architecture. There is still debate about whether hippocampal malrotation has pathologic significance. We present findings from the Consequences of Prolonged Febrile Seizures in Childhood (FEBSTAT) study on the frequency of and risk factors for hippocampal malrotation.

SUBJECTS AND METHODS

FEBSTAT is a prospective multicenter study investigating the consequences of febrile status epilepticus in childhood. MRI studies of 226 patients with febrile status epilepticus were analyzed visually by two board-certified neuroradiologists blinded to clinical details and were compared with MRI studies of 96 subjects with first simple febrile seizure. Quantitative analysis of hippocampal volume was performed by two independent observers.

RESULTS

Hippocampal malrotation was present in 20 of 226 (8.8%) patients with febrile status epilepticus compared with two of 96 (2.1%) control subjects (odds ratio [OR], 4.56; 95% CI, 1.05-19.92). Hippocampal malrotation was exclusively left-sided in 18 of 22 (81.8%) patients and bilateral in the remaining four patients (18.2%). There was no case of exclusively right-sided hippocampal malrotation. Hippocampal malrotation was more common in boys than in girls (OR, 6.1; 95% CI, 1.7-21.5). On quantitative volumetric MRI analysis, the left hippocampal volume was smaller in patients with hippocampal malrotation than in control subjects with simple febrile seizure (p = 0.004), and the right-to-left hippocampal volume ratio was higher in the hippocampal malrotation group than in the simple febrile seizure group (p < 0.001).

CONCLUSION

Hippocampal malrotation is a developmental malformation that predominantly affects the left hippocampus in male patients and is more frequently found in children with prolonged febrile status epilepticus than in control subjects. These data provide further evidence that hippocampal malrotation represents a pathologic error in brain development rather than a normal variant.

Do seizures and epileptic activity worsen epilepsy and deteriorate cognitive function?

Relevant to the definition of epileptic encephalopathy (EE) is the concept that the epileptic activity itself may contribute to bad outcomes, both in terms of epilepsy and cognition, above and beyond what might be expected from the underlying pathology alone, and that these can worsen over time. The review of the clinical and experimental evidence that seizures or interictal electroencephalography (EEG) discharges themselves can induce a progression toward more severe epilepsy and a regression of brain function leads to the following conclusions: The possibility of seizure-dependent worsening is by no means a general one but is limited to some types of epilepsy, namely mesial temporal lobe epilepsy (MTLE) and EEs. Clinical and experimental data concur in indicating that prolonged seizures/status epilepticus (SE) are a risky initial event that can set in motion an epileptogenic process leading to persistent, possibly drug-refractory epilepsies. The mechanisms for SE-related epileptogenic process are incompletely known; they seem to involve inflammation and/or glutamatergic transmission. The evidence of the role of recurrent individual seizures in sustaining epilepsy progression is ambiguous. The correlation between high seizure frequency and bad outcome does not necessarily demonstrate a cause-effect relationship, rather high seizure frequency and bad outcome can both depend on a particularly aggressive epileptogenic process. The results of EE studies challenge the idea of a common seizure-dependent mechanism for epilepsy progression/intellectual deterioration.

Origins of temporal lobe epilepsy: febrile seizures and febrile status epilepticus

Temporal lobe epilepsy (TLE) and hippocampal sclerosis (HS) commonly arise following early-life long seizures, and especially febrile status epilepticus (FSE). However, there are major gaps in our knowledge regarding the causal relationships of FSE, TLE, HS and cognitive disturbances that hamper diagnosis, biomarker development and prevention. The critical questions include: What is the true probability of developing TLE after FSE? Are there predictive markers for those at risk? A fundamental question is whether FSE is simply a marker of individuals who are destined to develop TLE, or if FSE contributes to the risk of developing TLE. If FSE does contribute to epileptogenesis, then does this happen only in the setting of a predisposed brain? These questions are addressed within this review, using information gleaned over the past two decades from clinical studies as well as animal models.

Are there really "epileptogenic" mechanisms or only corruptions of "normal" plasticity?

Plasticity in the nervous system, whether for establishing connections and networks during development, repairing networks after injury, or modifying connections based on experience, relies primarily on highly coordinated patterns of neural activity. Rhythmic, synchronized bursting of neuronal ensembles is a fundamental component of the activity-dependent plasticity responsible for the wiring and rewiring of neural circuits in the CNS. It is therefore not surprising that the architecture of the CNS supports the generation of highly synchronized bursts of neuronal activity in non-pathological conditions, even though the activity resembles the ictal and interictal events that are the hallmark symptoms of epilepsy. To prevent such natural epileptiform events from becoming pathological, multiple layers of homeostatic control operate on cellular and network levels. Many data on plastic changes that occur in different brain structures during the processes by which the epileptogenic aggregate is constituted have been accumulated but their role in counteracting or promoting such processes is still controversial. In this chapter we will review experimental and clinical evidence on the role of neural plasticity in the development of epilepsy. We will address questions such as: is epilepsy a progressive disorder? What do we know about mechanism(s) accounting for progression? Have we reliable biomarkers of epilepsy-related plastic processes? Do seizure-associated plastic changes protect against injury and aid in recovery? As a necessary premise we will consider the value of seizure-like activity in the context of normal neural development.

Risk factors for febrile status epilepticus: a case-control study

OBJECTIVE

To identify risk factors for developing a first febrile status epilepticus (FSE) among children with a first febrile seizure (FS).

STUDY DESIGN

Cases were children with a first FS that was FSE drawn from the Consequences of Prolonged Febrile Seizures in Childhood and Columbia cohorts. Controls were children with a first simple FS and separately, children with a first complex FS that was not FSE. Identical questionnaires were administered to family members of the 3 cohorts. Magnetic resonance imaging protocol and readings were consistent across cohorts, and seizure phenomenology was assessed by the same physicians. Risk factors were analyzed using logistic regression.

RESULTS

Compared with children with simple FS, FSE was associated with younger age, lower temperature, longer duration (1-24 hours) of recognized temperature before FS, female sex, structural temporal lobe abnormalities, and first-degree family history of FS. Compared with children with other complex FS, FSE was associated with low temperature and longer duration (1-24 hours) of temperature recognition before FS. Risk factors for complex FS that was not FSE were similar in magnitude to those for FSE but only younger age was significant.

CONCLUSIONS

Among children with a first FS, FSE appears to be due to a combination of lower seizure threshold (younger age and lower temperatures) and impaired regulation of seizure duration. Clinicians evaluating FS should be aware of these factors as many episodes of FSE go unnoticed. Further work is needed to develop strategies to prevent FSE.

Febrile seizures in rural Tanzania: hospital-based incidence and clinical characteristics

OBJECTIVE

Febrile seizures may contribute to epilepsy later in life, but data in sub-Saharan Africa are scarce. We, therefore, conducted a hospital-based study on clinical characteristics of children with febrile seizures.

METHODS

Over 2 years, we screened all pediatric admissions of Haydom Lutheran Hospital, northern Tanzania, and recruited 197 children with febrile seizures.

RESULTS

The incidence of febrile seizures was 4% of all admitted children aged <10 years, with a mortality of almost 4%. The peak age at the first febrile seizure was 2 years. One of five children experienced repeated episodes, and the majority of children showed features of complex seizures. Approximately 20% of children had a positive family history of febrile seizures or epilepsy.

CONCLUSION

Febrile seizures represent a frequent cause for admission of children, bearing a rather high mortality. Most children exhibit complex febrile seizures, which may contribute to the development of epilepsy later in life.

Prolonged febrile seizures, clinical characteristics, and acute management

PURPOSE

Prolonged febrile seizures (PFS) lasting ≥15 min have been associated with increased risk for epilepsy in later life. Initial treatment, mostly prehospital, aims to prevent its evolution to febrile status epilepticus (FSE) and reduce adverse outcome. Paucity of information is available on the immediate treatment before reaching a hospital facility.

METHODS

We obtained data, prospectively, on all children who presented from January 2008 to March 2010 with PFS to the emergency rooms of four Israeli medical centers. Information related to seizure semiology, treatment, and medical history was collected into a predefined pro forma form and reviewed centrally.

KEY FINDINGS

Sixty children, median age 18.3 months (interquartile range [IQR] 12-28) were included with a median seizure duration of 35 min (IQR 26-60), 43 (71.7%) lasting ≥30 min. Seizures had focal onset in 34 infants (57%). Fifty-four families (90%) activated the ambulance service; median ambulance arrival time was 8 min (IQR 5-10), 33 (61%) were medically treated by the ambulance paramedic, of whom 15 (45%) responded to treatment. Twelve children with active seizures did not receive medications. Initial treatment with rectal diazepam was more common in those with seizure duration >30 min.

SIGNIFICANCE

Most children with PFS are treated with antiepileptic drugs early by the ambulance service. However, even timely treatment does not prevent status epilepticus in the majority of cases. These data highlight the need for effective early treatment of this common pediatric emergency.

MRI abnormalities following febrile status epilepticus in children: the FEBSTAT study

OBJECTIVE

The FEBSTAT study is a prospective study that seeks to determine the acute and long-term consequences of febrile status epilepticus (FSE) in childhood.

METHODS

From 2003 to 2010, 199 children age 1 month to 5 years presenting with FSE (>30 minutes) were enrolled in FEBSTAT within 72 hours of the FSE episode. Of these, 191 had imaging with emphasis on the hippocampus. All MRIs were reviewed by 2 neuroradiologists blinded to clinical details. A group of 96 children with first simple FS who were imaged using a similar protocol served as controls.

RESULTS

A total of 22 (11.5%) children had definitely abnormal (n = 17) or equivocal (n = 5) increased T2 signal in the hippocampus following FSE compared with none in the control group (p < 0.0001). Developmental abnormalities of the hippocampus were more common in the FSE group (n = 20, 10.5%) than in controls (n = 2, 2.1%) (p = 0.0097) with hippocampal malrotation being the most common (15 cases and 2 controls). Extrahippocampal imaging abnormalities were present in 15.7% of the FSE group and 15.6% of the controls. However, extrahippocampal imaging abnormalities of the temporal lobe were more common in the FSE group (7.9%) than in controls (1.0%) (p = 0.015).

CONCLUSIONS

This prospective study demonstrates that children with FSE are at risk for acute hippocampal injury and that a substantial number also have abnormalities in hippocampal development. Follow-up studies are in progress to determine the long-term outcomes in these children.

Design and phenomenology of the FEBSTAT study

PURPOSE

Febrile status epilepticus (FSE) has been associated with hippocampal injury and subsequent hippocampal sclerosis (HS) and temporal lobe epilepsy. The FEBSTAT study was designed to prospectively examine the association between prolonged febrile seizures and development of HS and associated temporal lobe epilepsy, one of the most controversial issues in epilepsy. We report on the baseline phenomenology of the final cohorts as well as detailed aims and methodology.

METHODS

The "Consequences of Prolonged Febrile Seizures in Childhood" (FEBSTAT) study is a prospective, multicenter study. Enrolled are children, aged 1 month to 6 years of age, presenting with a febrile seizure lasting 30 min or longer based on ambulance, emergency department, and hospital records, and parental interview. At baseline, procedures included a magnetic resonance imaging (MRI) study and electroencephalography (EEG) recording done within 72 h of FSE, and a detailed history and neurologic examination. Baseline development and behavior are assessed at 1 month. The baseline assessment is repeated, with age-appropriate developmental testing at 1 and 5 years after enrollment as well as at the development of epilepsy and 1 year after that. Telephone calls every 3 months document additional seizures. Two other groups of children are included: a "control" group consisting of children with a first febrile seizure ascertained at Columbia University and with almost identical baseline and 1-year follow-up examinations and a pilot cohort of FSE from Duke University.

KEY FINDINGS

The FEBSTAT cohort consists of 199 children with a median age at baseline of 16.0 months (interquartile range [IQR] 12.0-24.0) and a median duration of FSE of 70.0 min (IQR 47.0-110.0). Seizures were continuous in 57.3% and behaviorally intermittent (without recovery in between) in 31.2%; most were partial (2.0%) or secondary generalized (65.8%), and almost all (98.0%) culminated in a generalized tonic-clonic seizure. Of the 199 children, 86.4% had normal development and 20% had prior febrile seizures. In one third of cases, FSE was unrecognized in the emergency department. The Duke existing cohort consists of 23 children with a median age of FSE onset of 18.0 months (IQR 14.0-28.0) and median duration of FSE of 90.0 min (IQR 50.0-170.0). The Columbia control cohort consists of 159 children with a first febrile seizure who received almost the same workup as the FEBSTAT cohort at baseline and at 1 year. They were followed by telephone every 4 months for a median of 42 months. Among the control cohort, 64.2% had a first simple FS, 26.4% had a first complex FS that was not FSE, and 9.4% had FSE. Among the 15 with FSE, the median age at onset was 14.0 months (IQR 12.0-20.0) and the median duration of FSE was 43.0 min (IQR 35.0-75.0).

SIGNIFICANCE

The FEBSTAT study presents an opportunity to prospectively study the relationship between FSE and acute hippocampal damage, the development of mesial temporal sclerosis, epilepsy (particularly temporal lobe epilepsy), and impaired hippocampal function in a large cohort. It is hoped that this study may illuminate a major mystery in clinical epilepsy today, and permit the development of interventions designed to prevent the sequelae of FSE.

Human herpesvirus 6 and 7 in febrile status epilepticus: the FEBSTAT study

PURPOSE

In a prospective study, Consequences of Prolonged Febrile Seizures in Childhood (FEBSTAT), we determined the frequency of human herpesvirus (HHV)-6 and HHV-7 infection as a cause of febrile status epilepticus (FSE).

METHODS

Children ages 1 month to 5 years presenting with FSE were enrolled within 72 h and received a comprehensive assessment including specimens for HHV-6 and HHV-7. The presence of HHV-6A, HHV-6B, or HHV-7 DNA and RNA (amplified across a spliced junction) determined using quantitative polymerase chain reaction (qPCR) at baseline indicated viremia. Antibody titers to HHV-6 and HHV-7 were used in conjunction with the PCR results to distinguish primary infection from reactivated or prior infection.

KEY FINDINGS

Of 199 children evaluated, HHV-6 or HHV-7 status could be determined in 169 (84.9%). HHV-6B viremia at baseline was found in 54 children (32.0%), including 38 with primary infection and 16 with reactivated infection. No HHV-6A infections were identified. HHV-7 viremia at baseline was observed in 12 children (7.1%), including eight with primary infection and four with reactivated infection. Two subjects had HHV-6/HHV-7 primary coinfection at baseline. There were no differences in age, characteristics of illness or fever, seizure phenomenology or the proportion of acute EEG or imaging abnormalities in children presenting with FSE with or without HHV infection.

SIGNIFICANCE

HHV-6B infection is commonly associated with FSE. HHV-7 infection is less frequently associated with FSE. Together, they account for one third of FSE, a condition associated with an increased risk of both hippocampal injury and subsequent temporal lobe epilepsy.

Prospects for imaging-related biomarkers of human epileptogenesis: a critical review

To facilitate the study of epileptogenesis in humans, noninvasive biomarkers of epileptogenesis are required. No validated biomarker is currently available, but brain imaging techniques provide many attractive candidates. In this article we examine the imaging features of temporal lobe epilepsy, focusing on those that may precede the onset of epilepsy and correlate with epileptogenesis. Hippocampal volumetry and T(2) relaxometry are proposed as candidate biomarkers of epileptogenesis in temporal lobe epilepsy following febrile status epilepticus. Preliminary data suggest that these have promise, and the ongoing Consequences of Prolonged Febrile Seizures in Childhood (FEBSTAT) study will provide more conclusive evidence as to their validity. At this time there are no other clear candidates for imaging-related biomarkers of epileptogenesis in human studies.

Clinical practice: the treatment of acute convulsive seizures in children

An adequate early treatment of a long-lasting convulsive seizure is critical in reducing potential morbidity, and in particular, brain damage. In pre-hospital settings the use of benzodiazepines should become standard. Nowadays, rectal diazepam is used frequently, but midazoloam and lorazepam are becoming more popular, both being given either intranasally or orally. The buccal route is to be preferred because of its easy use and high efficacy. A generally accepted policy for early treatment of convulsive seizures is a crucial issue in the elaboration of an overall treatment plan for the child with epilepsy. Such a plan should include instruction and education of the parents and the caregivers surrounding the child.

Long-term consequences of a prolonged febrile seizure in a dual pathology model

Clinical evidence suggests that febrile status epilepticus (SE) in children can lead to acute hippocampal injury and subsequent temporal lobe epilepsy. The contribution of febrile SE to the mechanisms underlying temporal lobe epilepsy are however poorly understood. A rat model of temporal lobe epilepsy following hyperthermic SE was previously established in our laboratory, wherein a focal cortical lesion induced at postnatal day 1 (P1), followed by a hyperthermic SE (more than 30 min) at P10, leads to hippocampal atrophy at P22 (dual pathology model) and spontaneous recurrent seizures (SRS) with mild visuospatial memory deficits in adult rats. The goal of this study was to identify the long term electrophysiological, anatomical and molecular changes in this model. Following hyperthermic SE, all cortically lesioned pups developed progressive SRS as adults, characterized by the onset of highly rhythmic activity in the hippocampus. A reduction of hippocampal volume on the side of the lesion preceded the SRS and was associated with a loss of hippocampal neurons, a marked decrease in pyramidal cell spine density, an increase in the hippocampal levels of NMDA receptor NR2A subunit, but no significant change in GABA receptors. These findings suggest that febrile SE in the abnormal brain leads to hippocampal injury that is followed by progressive network reorganization and molecular changes that contribute to the epileptogenesis as well as the observed memory deficits.

Neuroimaging biomarkers of epileptogenesis

Much progress has been made in the field studying the process of epileptogenesis via neuroimaging techniques. Conventional imaging methods include magnetic resonance imaging with morphometric analysis, magnetic resonance spectroscopy and positron emission tomography. Newer network-based methods such as diffusion tensor imaging and functional magnetic resonance imaging with resting functional connectivity are being developed and applied to clinical use. This review provides a brief summary of the major human and animal studies in both partial and generalized epilepsies that demonstrate the potential of these imaging modalities to serve as biomarkers of epileptogenesis.

Febrile status epilepticus: current state of clinical and basic research

Febrile status epilepticus occurs in up to 5% of all cases of febrile seizures and has been linked to the development of focal epilepsy. This article reviews the clinical characteristics and treatment issues of febrile status. Controversy exists regarding the relationship of febrile status epilepticus to the subsequent development of epilepsy. This subject is discussed by first reviewing the clinical research literature and then highlighting the basic science research regarding this controversial question. The current literature appears to support a role for febrile status in the development of focal epilepsy but is clearly neither necessary nor sufficient in the focal epileptogenisis process. Multiple insults are likely necessary for a child with febrile status epilepticus to develop epilepsy later in life.

Relevance of basic research to clinical data: good answers, wrong questions!

Do early seizures beget seizures later in life? Clinical data and experimental observations seem to answer that question differently, with a no and a yes, respectively, which may stem from an inadequate readout of what experimental data actually do tell us and a possible simplification of what clinical data indicate. Using specific experimental examples, it is possible to show that in the developing brain, seizures do produce long-lasting alterations of neuronal excitability, although ongoing seizures are not observed in adults. The findings suggest that the long-lasting changes in developmental programs and network activity that seizures induce do not necessarily lead to epilepsy, unless other events that remain to be identified occur.

Clinical MRI in children and adults with focal epilepsy: a critical review

Hippocampal sclerosis in adults and focal cortical dysplasia in children with epilepsy are frequent lesions, but they are overlooked on standard MRI. Errors in the interpretation of MRI in epilepsy can be attributed mainly to poor technique and perceptual misses, but incomplete knowledge and poor judgment are also possible sources. This review covers what to expect in structural MRI of an adult patient with mesial temporal lobe epilepsy (TLE) and how to find hippocampal sclerosis (HS). It also covers the clinical MRI-based detection of focal cortical dysplasia (FCD) in extratemporal lobe epilepsy, mainly in children. In a stepwise approach, first, a typical epilepsy MRI protocol at 1.5 T includes axial and coronal fluid-attenuated inversion recovery (FLAIR) imaging, T2- and T2 *-weighted images, and a T1-weighted, three-dimensional volume acquisition. Advanced MR techniques (quantitation, new contrasts like diffusion, MR spectroscopy, high-contrast high-resolution imaging on high-field MR scanners > or = 3 T) are used to increase the method's sensitivity to detect a lesion in an individual patient. Exploiting increased sensitivity, we can avoid false-positive results in the light of a clinical hypothesis, possibly isolating a localized brain area by seizure semiology and EEG prior to MR reading.

Development of hippocampal sclerosis after a complex febrile seizure

The role of prolonged febrile seizures in the genesis of hippocampal sclerosis is controversial; statistical analysis and data from epilepsy surgery suggest a causal relationship. A three-year-old boy had an initial febrile seizure with a transient postictal flaccid hemiparesis. Magnetic resonance imaging (MRI) showed no abnormality of the hippocampal areas of both sides. At the age of four a prolonged febrile seizure occurred. An MRI was done immediately and gave abnormal results in the right hippocampal area where T2-weighted and dark fluid sequences showed increased signal intensity; in diffusion-weighted sequences this region appeared hyperintense, which is in agreement with acute neuronal damage. Six weeks later the right hippocampal region still gave hyperintense signals in MRI (T2-weighted), while the diffusion coefficient was unremarkable. A final MRI scan was done 16 months following the second febrile seizure where the right hippocampal region still gave hyperintense signals and was reduced in size as is typical for hippocampal sclerosis. This case illustrates the development of a hippocampal lesion following a prolonged focal febrile seizure without any preexisting hippocampal lesion or positive family history. This suggests that prolonged febrile seizures alone can be a causative factor of hippocampal sclerosis.

Cognitive dysfunction after experimental febrile seizures

While the majority of children with febrile seizures have an excellent prognosis, a small percentage are later discovered to have cognitive impairment. Whether the febrile seizures produce the cognitive deficits or the febrile seizures are a marker or the result of underlying brain pathology is not clear from the clinical literature. We evaluated hippocampal and prefrontal cortex function in adult rats with a prior history of experimental febrile seizures as rat pups. All of the rat pups had MRI brain scans following the seizures. Rats subjected to experimental febrile seizures were found to have moderate deficits in working and reference memory and strategy shifting in the Morris water maze test. A possible basis for these hippocampal deficits involved abnormal firing rate and poor stability of hippocampal CA1 place cells, neurons involved in encoding and retrieval of spatial information. Additional derangements of interneuron firing in the CA1 hippocampal circuit suggested a complex network dysfunction in the rats. MRI T2 values in the hippocampus were significantly elevated in 50% of seizure-experiencing rats. Learning and memory functions of these T2-positive rats were significantly worse than those of T2-negative cohorts and of controls. We conclude that cognitive dysfunction involving the hippocampus and prefrontal cortex networks occur following experimental febrile seizures and that the MRI provides a potential biomarker for hippocampal deficits in a model of prolonged human febrile seizures.

Hippocampal MRI signal hyperintensity after febrile status epilepticus is predictive of subsequent mesial temporal sclerosis

OBJECTIVE

The objective of our study was to test the hypothesis that the finding of hyperintense hippocampal signal intensity on T2-weighted MR images soon after febrile status epilepticus is associated with subsequent hippocampal volume loss and persistent abnormal signal intensity on T2-weighted images (i.e., mesial temporal sclerosis).

SUBJECTS AND METHODS

Eleven children (mean age, 25 months) underwent initial MRI that included coronal temporal lobe imaging within 72 hours of febrile status epilepticus and follow-up imaging from 3 to 23 months later (mean, 9 months). A neuroradiologist blinded to clinical history graded initial and follow-up hippocampal signal intensity on a scale from 0 (normal) to 4 (markedly increased). Two blinded observers measured hippocampal volumes on initial and follow-up MR studies using commercially available software and volumes from 30 healthy children (mean age, 6.3 years). Initial signal intensity and hippocampal volume changes were compared using Kendall tau correlation coefficients.

RESULTS

On initial imaging, hyperintense signal intensity ranging from 1 (minimally increased) to 4 (markedly increased) was seen in seven children. Four children had at least one hippocampus with moderate or marked signal abnormality, three children had a hippocampus with mild or minimal abnormality, and four children had normal signal intensity. The Kendall tau correlation coefficient between signal intensity increase and volume change was -0.68 (p < 0.01). Five children (two with temporal lobe epilepsy and two with complex partial seizures) had hippocampal volume loss and increased signal intensity on follow-up imaging, meeting the criteria for mesial temporal sclerosis.

CONCLUSION

MRI findings of a markedly hyperintense hippocampus in children with febrile status epilepticus was highly associated with subsequent mesial temporal sclerosis.

[Relevance of basic research to clinical data: Good answers, wrong questions!]

What conclusions can be derived from experimental data on human epilepsies? This review discusses these issues, notably concerning human temporal lobe epilepsies (TLEs) and infantile epilepsies, where important advances have been achieved in both theory and the comprehension of epileptogenic mechanisms. A wide spectrum of human and animal data converge to show that the naive network transforms to one that generates seizures spontaneously. Thus, in TLE, experimental and human data suggest that the inaugurating status generates a sequence of events that lead to the sprouting of fibers and the formation of novel excitatory synapses. This reactive plasticity constitutes a basis for the generation of novel seizures by the epileptic network. Similarly, in vitro studies indicate that in immature hippocampal formation, the propagation of high- but not low-frequency seizures can transform a naive network into one that generates further seizures, thereby, giving an indication as to the types of seizure that are epileptogenic. In conclusion, it is suggested that although animal data cannot mimic human seizures in all their complex and variable etiologies, it provides essential indications on the mechanisms that enable seizure generation.

Special issues in the management of young children, older adults, and the developmentally disabled

The very young, the very old, and those with developmental disability have an increased risk of both epilepsy and prolonged and repetitive seizures. The special issues that affect their management are reviewed. Polypharmacy that occurs because of comorbid illnesses requiring chronic medication can result in dangerous drug-drug interactions. The antiepileptic drug's pharmacokinetic profile must be factored when treating young children and older adults. Patients who have taken an older enzyme-inducing antiepileptic drug for years may have a markedly induced hepatic enzyme system that may alter drug metabolism. Overdose or toxicity may occur in older adults who may metabolize and clear antiepileptic drugs more slowly than younger patients. Benzodiazepines are the most rapidly effective acute therapy for repetitive or prolonged seizures. It is important to have a plan for management of prolonged and repetitive seizures. Long-term therapy should be managed in a manner that will eliminate the need for rescue therapies and visits to the emergency department.

Effects of seizures on developmental processes in the immature brain

Infants and children are at a high risk for seizures compared with adults. Although most seizures in children are benign and result in no long-term consequences, increasing experimental animal data strongly suggest that frequent or prolonged seizures in the developing brain result in long-lasting sequelae. Such seizures may intervene with developmental programmes and lead to inadequate construction of cortical networks rather than induction of neuronal cell loss. As a consequence, the deleterious actions of seizures are strongly age dependent: seizures have different effects on immature or migrating neurons endowed with few synapses and more developed neurons that express hundreds of functional synapses. This differential effect is even more important in human beings and subhuman primates who have an extended brain development period. Seizures also beget seizures during maturation and result in a replay of development programmes, which suggests that epileptogenesis recapitulates ontogenesis. Therefore, to understand seizures and their consequences in the developing brain, it is essential to determine how neuronal activity modulates the main steps of cortical formation. In this Review, we present basic developmental principles obtained from animal studies and examine the long-lasting consequences of epilepsy.

Do Early Hippocampal Imaging Changes Predict Later Sclerosis?

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

Risk of intracranial pathologic conditions requiring emergency intervention after a first complex febrile seizure episode among children

OBJECTIVE

To determine the likelihood of intracranial pathologic conditions requiring emergency neurosurgical or medical intervention among children without meningitis who presented to the pediatric emergency department after a first complex febrile seizure.

METHODS

We performed a retrospective review of prospectively collected data for children in neurologically normal condition who presented to a single pediatric emergency department after a first complex febrile seizure (focal, multiple, or prolonged). The complex febrile seizure classification was determined independently by 2 epileptologists. The presence of intracranial pathologic conditions was determined through review of neuroimaging results, telephone interviews, or medical record review.

RESULTS

Data for 71 children with first complex febrile seizures were analyzed. Fifty-one (72%) had a single complex feature (20 focal, 22 multiple, and 9 prolonged), and 20 (28%) had multiple complex features. None of the 71 patients (1-sided 95% confidence interval: 4%) had intracranial pathologic conditions that required emergency neurosurgical or medical intervention.

CONCLUSIONS

For children with first complex febrile seizures, the risk of intracranial pathologic conditions that require emergency neurosurgical or medical intervention is low, which suggests that routine emergency neuroimaging for this population is unnecessary.

Hippocampal sclerosis in severe myoclonic epilepsy in infancy: a retrospective MRI study

PURPOSE

Severe myoclonic epilepsy in infancy (SMEI; Dravet's syndrome) is a malignant epilepsy syndrome characterized by early prolonged febrile convulsions (PFCs) with secondary psychomotor delay and a variety of therapy-resistant seizures. Although the initial symptoms are repeated PFCs, the MRI performed at the onset of disease shows no hippocampal structural abnormalities. We aimed to assess clinical and serial MRI data of patients with SMEI with a special attention to the temporomedial structures. To our knowledge, this is the first systematic MRI study in this disease.

METHODS

Clinical and MRI data of all SMEI patients treated in our hospitals between 1996 and 2004 were reviewed.

RESULTS

Twenty-eight MRIs from 14 children (one to four images/patient) were included. Age at disease onset was between 3 and 9 months; age at initial MRI was 5 months to 13 years. Ten of 14 patients showed hippocampal sclerosis (HS) during the course of the disease (nine unilateral, one bilateral). Six of these 10 had a normal initial MRI. Age at the first verified HS was between 14 months and 13 years. Neither complex partial seizures nor anterior temporal irritative zone was recorded in these children.

CONCLUSIONS

After initially normal structures, in most patients with SMEI, HS develops several months or years after the first PFC. These data support the hypothesis that PFC might be responsible for HS, but other factors and individual sensitivity should play a role in this process.

Serial MRI after experimental febrile seizures: altered T2 signal without neuronal death

Whereas most febrile seizures (FSs) carry a benign outcome, a subpopulation of individuals with prolonged FSs are at risk for later temporal lobe epilepsy. Signal changes on magnetic resonance imaging (MRI) may provide early markers for changes in neuronal integrity that may promote epileptogenesis in such individuals. Here, we used serial MRIs, obtained before and at several time points after experimental prolonged FSs, to determine the prevalence and distribution of signal changes on T2-weighted images and to investigate the pathological substrates leading to these changes. Seventy-five percent of immature rats with experimental prolonged FSs had abnormal T2 signal enhancement at 24 hours, and 87.5% at 8 days after the seizures. The altered T2 values involved the dorsal hippocampus (75%), the piriform cortex (87.5%), and the amygdala (25%). However, these changes were not accompanied by evidence of neuronal injury or death in these regions, as assessed using the Fluoro-Jade method. Thus, experimental prolonged FSs lead to relatively frequent abnormal MRI signal in "temporal lobe" structures. Although these changes do not signify cell death, they may denote pathological cellular processes that promote epileptogenesis. .

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

INTRODUCTION

Proton magnetic resonance spectroscopy ((1)H MRS) has been proposed as a lateralizing method for the presurgical evaluation of patients with medically intractable temporal lobe epilepsy (TLE). Studies have shown correlations between temporal lobe (TL) NAA and seizure frequency, and TL NAA/Cr and the duration of epilepsy in patients with TLE. This latter finding may suggest that progressive neuronal dysfunction may occur in both temporal lobes in patients with TLE, even when the seizures originate in only one temporal lobe. We analyzed our data in an attempt to find a possible correlation between extension of neuronal dysfunction based on NAA measures and duration of epilepsy.

METHODS

We studied 45 consecutive patients with the diagnosis of TLE, who were referred for presurgical evaluation. Duration of epilepsy was defined as the interval between the age of seizure onset and the time of the MRS examination. All studies were performed in the inter-ictal state, prior to intracranial monitoring or resection. We performed two-tailed Pearson correlation analysis between ipsilateral NAA/Cr and extension of the abnormality (voxels involved) and the duration of the seizure disorder in years.

RESULTS

The average duration of epilepsy in this group was 20 years. No significant correlation was found between duration of epilepsy and mean hippocampal NAA/Cr (r=-.131, p=.390); nor was a correlation found between duration of epilepsy in years or the extent of metabolic lesion (voxels involved) (r=-.264, p=.079).

CONCLUSIONS

Hippocampal NAA/Cr does not correlate with duration of epilepsy in TLE. Our findings suggest that cross-sectional group measures of hippocampal neuronal function do not suggest damage progression.

Cognitive impairment following status epilepticus and recurrent seizures during early development: support for the "two-hit hypothesis"

Prolonged seizures in immature rats result in minimal behavioral consequences when the animals are studied later in life. Likewise, early-onset seizures are associated with minimal morphological changes. However, it is known that seizures early in life result in changes in the brain that make it more vulnerable to subsequent seizure-induced injury (the so-called two-hit hypothesis). Whether this heightened vulnerability occurs immediately after the first seizure is not known. In this study, immature rats were exposed to status epilepticus (SE) followed by a series of 25 flurothyl-induced seizures, SE alone, 25 flurothyl-induced seizures alone, or no seizures. Rats exposed to SE and flurothyl seizures performed significantly poorer in the water maze 2 weeks following the last seizure compared with the other groups. No histological lesions were seen in any of the four groups. This study suggests that SE renders the immature brain vulnerable to further seizure-induced injury and this enhanced vulnerability occurs very quickly after the SE.

"Tectonic" hippocampal malformations in patients with temporal lobe epilepsy

Histological analysis of hippocampi removed en bloc during surgical treatment of temporal lobe epilepsy revealed a subgroup of patients with bulbous expansions of the CA1 pyramidal cell/subicular layers that were consistently accompanied by "tectonic" invaginations of the adjacent dentate gyrus. Most hippocampi containing the CA1/subicular anomaly and the tectonically deformed dentate gyrus exhibited minor cell loss compared to hippocampi with typical hippocampal sclerosis, and retrospective analysis revealed that conventional imaging methods usually failed to detect subtle hippocampal atrophy or abnormal signal characteristics in patients with this anomaly. Cells within the anomaly exhibited the spherical appearance of undifferentiated pyramidal layer neurons, and were immunopositive for the neuronal marker NeuN. Immunostaining for the synaptic marker beta-synuclein suggested abnormal dentate gyrus lamination in segments containing the pyramidal cell layer anomaly, but not in unaffected areas of the same specimens. Despite differences in the extent of neuronal loss between patients with hippocampal sclerosis and those with the CA1/subicular anomaly, the incidence of antecedent febrile seizures was similar in both groups. In a comparison group of hippocampi obtained at autopsy, structural irregularities were evident, but were consistently less disruptive to hippocampal architecture than the anomalies observed in epilepsy patients. We hypothesize that developmental malformation of the CA1 pyramidal cell/subicular layers may adversely influence the subsequent development of the adjacent dentate gyrus, and may render temporal lobe structures hyperexcitable and more vulnerable to relatively innocuous seizures and injuries. Thus, these presumably developmental hippocampal anomalies may serve as substrates for early febrile seizures and subsequent epilepsy.

Status epilepticus in immature rats leads to behavioural and cognitive impairment and epileptogenesis

It remains under dispute whether status epilepticus (SE) in the perinatal period or early childhood or the underlying neuropathology is the cause of functional impairment later in life. The present study examined whether SE induced by LiCl-pilocarpine in normal immature brain (at the age of 12 or 25 days; P12 or P25) causes cognitive decline and epileptogenesis, and the data were compared to those of rats undergoing SE as adults. Rats in the P12 group had impaired memory (repeated exposure to open-field paradigm) and emotional behaviour (lower proportion of open-arm entries and higher incidence of risk assessment period in elevated plus-maze) when assessed 3 months after SE, although not as severe as in the older age groups. Importantly, video-electroencephalography monitoring 3 months after SE demonstrated that 25% of rats in the P12 and 50% in P25 group developed spontaneous seizures. Only nonconvulsive seizures (ictal activity in hippocampus accompanied by automatisms) were recorded in the P12 group whereas rats in the P25 group exhibited clonic convulsions. The present findings indicate that SE is harmful to the immature brain as early as P12, which might be compared with early infancy in humans.

Mechanisms of epilepsy progression: current theories and perspectives from neuroplasticity in adulthood and development

Clinical and epidemiological studies have repeatedly demonstrated that a subset of patients with epilepsy have progressive syndromes with increasing seizure frequency and cumulative adverse effects despite optimal anticonvulsant therapy. Recent longitudinal imaging studies and long-term neuropsychological studies have confirmed that a substantial subset of people with epilepsy undergo progressive brain atrophy accompanied by functional declines that worsen with duration of epilepsy. As further evidence of the progressive and adverse effects of inadequately controlled epilepsy, chronic experimental models of epilepsy and the phenomenon of kindling have provided abundant evidence that neural circuits undergo long-term progressive structural and functional alterations in response to seizures. This long-term seizure-induced plasticity in neural circuits appears to be "bidirectional", inducing progressive damage while also inducing resistance to additional damage, as a function of timing or inter-seizure interval. Seizure-induced plasticity has pronounced age-dependence, and influences long-term cognitive consequences of seizures during early life and acquired susceptibility to epilepsy in adulthood. While it is clear from clinical and epidemiological studies that human epilepsy is a heterogeneous disorder and that not all epileptic syndromes are progressive, emerging results from studies of activity-dependent and seizure-induced plasticity and perspectives from "complex systems" analysis are providing new insights into systematic neurobiological processes that are likely to influence the progressive features of epileptic syndromes and patterns of progression in individual patients. The emerging perspective is that phenomena of plasticity and genetic background exert powerful effects in development and adulthood through regulation of activity-dependent structural and functional remodeling of neural circuitry, and that these effects not only influence progression and consequences of seizures, but also offer new opportunities for therapeutic intervention.