Frontal lobe epilepsy: the next frontier

Cognitive Impairment in MRI-Negative Epilepsy: Relationship between Neurophysiological and Neuropsychological Measures

BACKGROUND

Epileptic patients frequently encounter cognitive impairment. Functions that are mostly affected involve memory, attention, and executive function; however, this is mainly dependent on the location of the epileptic activity. The aim of the present study is to assess cognitive functions in MRI-negative epilepsy patients by means of neurophysiological and neuropsychological measures, as well as study the concept of transient cognitive impairment in patients with epileptiform discharges during EEG acquisition.

METHODS

The patients were enrolled from an outpatient Epilepsy/Clinical Neurophysiology clinic over a time period of 6 months. The study sample comprised 20 MRI-negative epilepsy patients (mean age ± standard deviation (SD), 30.3 ± 12.56 years; age range, 16-60 years; average disease duration, 13.95 years) and 10 age-matched controls (mean age ± SD, 24.22 ± 15.39 years), who were also education-matched (p > 0.05). Patients with epileptogenic lesions were excluded from the study. Informed consent was obtained from all subjects involved in the study. Auditory ERPs and the cognitive screening tool EpiTrack were administered to all subjects.

RESULTS

Latencies of P300 and slow waves were prolonged in patients compared to controls (p < 0.05). The ASM load and patients' performance in the EpiTrack maze subtest were the most significant predictors of P300 latency. A decline in the memory, attention, and speed of information processing was observed in patients with cryptogenic epilepsy compared to age-matched controls, as reflected by P300 latency and EpiTrack scores.

Deep phenotyping of frontal lobe epilepsy compared to other epilepsy syndromes

AIMS

Frontal lobe epilepsy (FLE) is understudied and often misdiagnosed. We sought to comprehensively phenotype FLE and to differentiate FLE from other focal and generalised epilepsy syndromes.

METHODS

This was a retrospective, observational cohort study of 1078 cases of confirmed epilepsy in a tertiary neurology centre in London. Data sources were electronic health records, investigation reports and clinical letters.

RESULTS

166 patients had FLE based on clinical findings and investigations-97 with identifiable electroencephalography (EEG) foci in frontal areas (definite FLE), while 69 had no frontal EEG foci (probable FLE). Apart from EEG findings, probable and definite FLE did not differ in other features. FLE was distinct from generalized epilepsy, which tended to present with tonic-clonic seizures and be due to genetic causes. FLE and temporal lobe epilepsy (TLE) both featured focal unaware seizures and underlying structural or metabolic aetiology. FLE, TLE and generalized epilepsy differed in their EEG (P = 0.0003) and MRI (P = 0.002) findings, where FLE had a higher rate of normal EEG and abnormal MRI findings compared to TLE.

CONCLUSIONS

EEG is often normal for FLE, and abnormalities are commonly identified with MRI. There was no difference in the clinical features of definite and probable FLE, suggesting they represent the same clinical entity. The diagnosis of FLE can be made even when scalp EEG is normal. This large medical cohort provides hallmark features of FLE that differentiate it from TLE and other epilepsy syndromes.

Orbitofrontal epilepsy: Case series and review of literature

BACKGROUND

Orbitofrontal epilepsy (OFE) is less known and is poorly characterized in comparison with temporal lobe epilepsy, partly because it is rare and possibly because it is unrecognized and therefore underestimated.

OBJECTIVE

This paper aimed to better characterize seizure semiology, presurgical findings, and surgical outcomes in patients with OFE.

METHODS

We retrospectively reviewed all confidently established OFE cases from six Canadian epilepsy monitoring units between 1988 and 2014, and in the literature between 1972 and 2017. Inclusion criteria were identification of an epileptogenic lesion localized in the OFC or if the patient was seizure-free after surgical removal of the OFC in nonlesional cases.

RESULTS

Sixteen cases were identified from our databases. Fifty percent had predominantly sleep-related seizures; 56% had no aura (the remaining had nonspecific or vegetative auras), and 62.5% featured hypermotor (mostly hyperkinetic) behaviors. Interictal epileptiform discharges over frontal and temporal derivations always allowed lateralization. Magnetic resonance imaging (MRI) identified an orbitofrontal lesion in 8/16, positron emission tomography (PET) identified a hypometabolism extending outside the orbital cortex in 4/9, ictal single-photon emission computed tomography (SPECT) identified an orbital hyperperfusion in 1/5, magnetoencephalography (MEG) identified lateral orbital sources in 2/4, and intracranial electroencephalography (EEG) identified an orbitofrontal onset in 9/10. Fourteen patients underwent surgery, all reaching a favorable outcome (71.4% Engel 1; 28.6% Engel 2; mean FU=5.6years). Pre- and postoperative neuropsychological assessments revealed heterogeneous findings. Our review of literature identified 71 possible cases of OFE, 32 with confident focus localization. Extracted data from these cumulated cases supported observations made from our case series.

CONCLUSIONS

Orbitofrontal epilepsy should be suspected with sleep-related, hyperkinetic seizures with no specific aura, and frontotemporal interictal discharges. Several patients have nonmotor seizures with or without auras which may resemble temporal lobe seizures. Postoperative seizure outcome was favorable, but there is inherent bias as we only included patients with a seizure-free outcome if the MRI was negative. A larger study is required to address identified gaps in knowledge such as identifying discriminative features between medial and lateral OFE, evaluating the value of more recent diagnostic tools, and assessing the neuropsychological outcome of orbital epilepsy surgery.

Monozygotic twin sisters discordant for familial hemiplegic migraine

BACKGROUND

The high concordance rate of migraine in monozygotic twin pairs has long been recognised. In the current study, we present a monozygotic twin pair discordant for familial hemiplegic migraine (FHM).

CASE PRESENTATIONS

We evaluated 12 adult family members in 2012. The twin pair was separately examined by neurologists at different time points. Mutation screening was performed for known FHM-related genes. The monozygosity of the twins was verified. Eleven individuals had a history of migraine or paroxysmal neurological symptoms, including four patients with motor aura. No mutations were detected in the CACNA1A, ATP1A2, SCN1A, PRRT2 or NOTCH3 genes. The monozygotic twin sisters, aged 52, were discordant for age of onset, motor aura and neuropsychological aura (forced thinking). Overall, the family members presented a wide range of phenotypical features.

CONCLUSIONS

Familial hemiplegic migraine is a monogenic disorder that is distinct from migraine with typical aura. However, in certain families with motor aura, such as this one, it is possible that the most severe phenotype is caused by an unlikely combination of polygenic traits and non-genetic factors. In these kindreds, we propose that hemiplegic aura is only a severe and complex form of typical aura.

What makes a simple partial seizure complex?

The assessment of ictal consciousness has been the landmark criterion for the differentiation between simple and complex partial seizures over the last three decades. After review of the historical development of the concept of "complex partial seizure," the difficulties surrounding the simple versus complex dichotomy are addressed from theoretical, phenomenological, and neurophysiological standpoints. With respect to consciousness, careful analysis of ictal semiology shows that both the general level of vigilance and the specific contents of the conscious state can be selectively involved during partial seizures. Moreover, recent neuroimaging findings, coupled with classic electrophysiological studies, suggest that the neural substrate of ictal alterations of consciousness is twofold: focal hyperactivity in the limbic structures generates the complex psychic phenomena responsible for the altered contents of consciousness, and secondary disruption of the network involving the thalamus and the frontoparietal association cortices affects the level of awareness. These data, along with the localization information they provide, should be taken into account in the formulation of new criteria for the classification of seizures with focal onset.

Neurocognitive and behavioral functioning in frontal lobe epilepsy: a review

Frontal lobe epilepsy (FLE) is a seizure disorder with a lower prevalence than temporal lobe epilepsy (TLE). Despite its consequences on cognitive and emotional well-being, the neuropsychology of FLE has not been well studied. By contrast, TLE has been studied meticulously, leading to a relevant understanding of memory and the functional characteristics of the temporal and limbic circuits. The neuropsychological studies on FLE report deficits in motor coordination and planning, reduced attention span, and difficulties in response inhibition in complex cognitive tasks. This review aims to illustrate the most relevant neurocognitive dimensions, psychiatric comorbidity, and postoperative neuropsychological outcome of FLE. Methodological suggestions for future research are also included by critically reviewing the existing literature.

Frontal lobe seizures

Despite the fact that clinical characteristics of frontal lobe seizures have been recently described better, differentiating seizures of frontal lobe origin from NES on clinical grounds alone is difficult. The difficulty has been compounded by the fact that both inter-ictal and ictal EEG can be normal or nonspecific, and the same is true of imaging studies. A detailed clinical history as well as video monitoring can be helpful diagnostic tools. A multidisciplinary approach is warranted and is at times essential to improve the diagnosis and care of these difficult patients.

The Clinical Relevance of EEG Interpretation

There is need nowadays to re-emphasize the capabilities of electroencephalography: a method representing the extremely important function/dysfunction-orientation in neurological thinking and practice. Valuable and relevant messages to the clinician naturally require solid EEG training and the resulting expertise.

The idea that valuable EEG information is limited to the field of epileptology is erroneous. A plethora of clinically relevant messages can be derived from the EEG in nonepileptic conditions and, above all, in metabolic (and so called “mixed”) encephalopathies where neuroimaging has almost nothing to offer.

The discussion of EEG and epileptology only skirts pediatric conditions (and most of the epileptic syndromes). It is shown that EEG reading in epileptology is a lot more than simply “hunting spikes.” A strong plea is being made against the presently fashionable overuse of the term “non-convulsive status epilepticus.”

Continuing neglect of functional/dysfunctional orientation can seriously endanger the entire field of Neurology.

Electrophysiology of the frontal lobe

The electrophysiology of the frontal lobe appears to be unimpressive when the view is limited to the routine EEG recording of a healthy waking adult. There is usually low voltage fast activity, which becomes more pronounced when recorded with depth leads. Three special EEG patterns of marginal to slightly abnormal character are discussed: a) rhythmical midfrontal 6-7/sec activity of juveniles, b) rhythmical midfrontal sharp 4-6/sec activity of infancy and early childhood with arousal from sleep, and c) frontal intermittent rhythmical delta activity (FIRDA) in waking adults with frontopolar maximum, possibly related to thought processes under abnormal conditions. With extension of the frequency range, ultraslow (DC-like) as well as fast beta (gamma, 40-80/sec) and ultrafast activity (80-1000/sec) are found particularly over the frontal lobes. Ultraslow baseline shifts are arousal-related and mixed with overlying ultrafast waves. Attention control and the "working memory" involve chiefly the dorsolateral prefrontal cortex, investigated with P300 responses and likely to show ultrafast spectra. Perception-related 40-80/sec gamma activity has been thought to be associated with the entrance into consciousness. Initiation and design of motor activity spreads from prefrontal to the frontomotor cortex, associated with powerful event-related potentials: contingent negative variation (CNV) and "Bereitschafts potential" ("readiness potential," RP). Neuroscientific research of the highest frontal lobe functions has become a very active domain of neuroimaging. With the use of the extended frequency range, EEG and also evoked potential studies could add further information with acquisition in real time. Ultrafast frequency ranges presented in computerized frequency analysis and mapping might show impressive correlates of highest frontal lobe functions.

Social communication in children with epilepsy

BACKGROUND

This study examined measures of social communication that involve the use of language in formulating and organizing thoughts and its relationship with seizure-related, developmental, cognitive, and behavioral variables in 92 children with complex partial seizure disorder (CPS), 51 with primary generalized epilepsy (PGE), and 117 normal children, aged 5.1-16.9 years.

METHODS

Coding the children's speech samples with the Kiddie Formal Thought Disorder Rating Scale (Caplan et al., 1989) and Halliday and Hasan's (1976) analysis of cohesion demonstrated social communication deficits in both seizure disorder groups.

RESULTS

The CPS patients had both formal thought disorder and cohesion deficits and the PGE group had mild cohesion deficits. IQ, as well as fronto-temporal and bilateral spike and wave activity were associated with the severity of the social communication deficits of the CPS group. The social communication deficits of the PGE group, however, were related to IQ and seizure control.

CONCLUSIONS

Recurrent CPS and PGE and fronto-temporal localization of epileptic activity might impair the development of children's communication skills.

Runner-up in the young physician's section of the Gowers' prize 2000. Epilepsy and the physical basis of consciousness

The issue of human consciousness, in both its popular and neuroscientific sense, is considered from a clinical perspective. The ictal semiologies of the various epilepsies, together with associated clinical features, are demonstrated to highlight certain neuroanatomical and neurophysiological facets of consciousness. It is suggested that further insights into consciousness, even those bordering on the philosophical, may be led by clinical neurological phenomena and emerging neuroinvestigative techniques.

Conversational repair in pediatric epilepsy

This study examined if children with complex partial seizures disorder (CPS) and primary generalized epilepsy with absence (PGE) were impaired in the use of self-initiated repair during a conversation compared to normal children. Transcriptions of speech samples of 92 CPS, 51 PGE, and 65 normal children, ages 5-16 years, were coded for self-initiated repair according to Evans (1985). The WISC-R, a structured psychiatric interview, and seizure-related information were obtained for each child. We found impaired use of repair in both the CPS and PGE groups compared to the normal subjects. The CPS patients, particularly those with a temporal lobe focus, overused self-initiated corrections of referents and syntax compared to the PGE and normal subjects. The CPS and PGE patients with frontal lobe involvement underused fillers compared to the normal children. These findings provide additional evidence that both CPS and PGE impact the ongoing development of children's communication skills.

The Frontal Lobes, Epilepsy, and Behavior

The frontal lobes have been overshadowed by the temporal lobes in the vast literature addressing the neurobehavioral and psychological perspectives of epilepsy. The purpose of this review is to summarize contemporary anatomicobehavioral correlations and to highlight the frontal lobe contributions to the neurology, neuropsychology, and neuropsychiatry of epilepsy, in general, and to temporal lobe epilepsy (TLE) and frontal lobe epilepsy (FLE), in particular. Much evidence has accumulated suggesting that focal epileptogenic tissue may have effects on distant neural systems. Data supporting the case that the frontal regions are preferentially affected in TLE are presented. Emphasis is placed on the results of numerous functional imaging studies demonstrating correlations between frontal hypoperfusion and cognitive or mood impairments in patients with TLE.

Intractable seizures of frontal lobe origin: clinical characteristics, localizing signs, and results of surgery

PURPOSE

We analyzed the clinical characteristics of seizures of frontal lobe (FL) origin with particular emphasis on establishing different categories and determining if these categories had any localizing or lateralizing value. In addition, results of surgery are reported.

METHODS

Seizure characteristics were established by historical review and electroencephalographic/videotape analysis of 449 seizures in 26 adult patients with refractory seizures of FL origin.

RESULTS

No outstanding risk factor was identified for seizures of FL origin. Seizures were frequent (7.1 per week), brief (mean duration, 48.3 seconds), and had a nocturnal preponderance in 58% of the patients. Status epilepticus was reported in 54%, and generalized convulsions as a prominent seizure type were reported in 26% of patients. The most common reported aura was a nonspecific sensation, often localized to the head (35%). Early forced head and eye deviation was not a consistent lateralizing sign, whereas late head and eye deviation always occurred contralateral to the site of seizure origin. Early asymmetric tonic posturing occurred consistently contralateral to the side of seizure origin. Clinical seizure patterns did not consistently localize to specific regions of the frontal lobe, although there were some noticeable trends: focal clonic seizures were associated with seizure origin in the frontal convexity; tonic seizures were most often associated with origin in the supplementary motor area but also occurred with origin in other parts of the frontal lobe; seizures resembling typical temporal lobe seizures with oroalimentary automatisms were observed with seizure origin in the orbitofrontal region; and seizures with hyperactive, frenetic automatisms were not associated with any specific region within the frontal lobes. Eighty percent of patients had favorable seizure outcome after surgery (class I/II).

CONCLUSION

Although certain clinical features are characteristic for seizures of frontal lobe origin and some have lateralizing value, they do not localize to specific areas within the FL. After careful presurgical evaluation, both lesional and nonlesional patients benefit from epilepsy surgery.

Absence seizures and the frontal lobe

There is no doubt that the frontal lobe plays a major role in the 3/sec spike-wave absence seizure. It is pointed out initially that the controversies of cortical vs. thalamic origin of the spike-waves and the associated absence can be laid at rest as far as human absence seizures and human primary generalized epilepsy (PGE) are concerned: their origin is cortical with maximal frontal lobe involvement. Experimentally-induced spike-wave bursts or spontaneous spike-waves in animals pertain to other forms of epileptic seizure disorder. The frontal maximum of the 3/sec spike-wave pattern indeed indicates maximal frontal lobe involvement including both prefrontal and frontomotor portions. The absence as such is presumed to be a suspension of the working memory--an eminently frontal lobe function. This explains the immediate restoration of ictally-impaired neurocognitive functions right at the termination of the seizures. This concept can be applied not only to the classical absence occurring in PGE but also to the rare cases of secondary bilateral synchrony with a primary frontal epileptogenic focus leading to true (though very slightly different) absences.

Cryptogenic gelastic epilepsy of frontal lobe origin: a paediatric case report

Gelastic (laughing) seizures are an uncommon seizure type which in most cases has an organic cerebral pathology and specifically a hypothalamic hamartoma. The interictal EEG frequently shows focal activity. This report describes a 3 1/2-year-old boy who presented with episodes of unmotivated laughter associated with other epileptic symptomatology before the age of 3 years. Prolonged ambulatory EEG monitoring recorded electroclinical seizures starting in the right frontal area and spreading to the adjacent frontotemporal region. Neurological examination and brain magnetic resonance imaging were normal. Vigabatrin resulted in immediate remission of the seizures and normalization of the EEG.