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Focal epilepsy: Causes and clinical features

Focal epilepsy: Causes and clinical features
Literature review current through: Sep 2023.
This topic last updated: Jun 28, 2022.

INTRODUCTION — Epilepsy is a disease associated with lasting derangement of brain function and predisposition to recurring seizures [1]. It may arise from a variety of genetic, structural, metabolic, immune, and infectious causes (table 1) [2-4]. Seizures and epilepsy are generally divided into focal and generalized according to the mode of seizure onset as well as into genetic, structural, metabolic, immune, infectious, or unknown according to the underlying cause or etiology. Focal or localization-related epilepsies have previously been referred to as partial epilepsies [5].

Most of the focal epilepsies are either structural or unknown, which means there is a presumed focal structural cause that cannot be identified historically or be seen with current imaging techniques. If the patient undergoes epilepsy surgery, the cause is sometimes subsequently defined pathologically. Focal epilepsies of childhood, including benign epilepsy of childhood with centrotemporal spikes and Panayiotopoulos syndrome, are of unknown cause but may have a genetic component.

The causes, clinical manifestations, and electroencephalographic features of the focal (localization-related) epilepsies are reviewed here. The focal epilepsies of childhood and those that occur exclusively or predominantly during sleep are discussed in detail separately. (See "Benign (self-limited) focal epilepsies of childhood" and "Sleep-related epilepsy syndromes".)

The management of focal epilepsy and other epilepsy syndromes are discussed separately. (See "Overview of the management of epilepsy in adults" and "Initial treatment of epilepsy in adults" and "Evaluation and management of drug-resistant epilepsy" and "Surgical treatment of epilepsy in adults" and "Seizures and epilepsy in children: Initial treatment and monitoring".)

ETIOLOGIES — Most of the focal epilepsies are the result of a structural brain abnormality, even though this cannot always be identified. These cases represent most cases of adult-onset epilepsy, although these are common in childhood as well. If imaging studies are normal, the cause remains unknown.

Hippocampal sclerosis — Hippocampal sclerosis (HS, also called mesial temporal sclerosis) is the most common pathological feature of temporal lobe epilepsy (TLE) [6]. Pathologic examination reveals neuronal loss in the hippocampus, predominantly involving the hilar region, CA1, CA3, CA4, and dentate gyrus, with relative sparing of the CA2 region. A classification scheme developed by a task force of the International League Against Epilepsy (ILAE) recognizes three pathological subtypes [7]:

HS ILAE type 1 is characterized by severe neuronal loss and gliosis predominantly involving CA1 and CA4. The CA1 segment is the most severely affected, with >80 percent cell loss, but all other segments also show significant neuronal cell loss. Approximately 60 to 80 percent of surgically resected specimens fall into this subtype.

HS ILAE type 2 is characterized by CA1-predominant neuronal cell loss and gliosis with sparing of cell numbers in CA2, CA3 and CA4.

HS ILAE type 3 is characterized by CA4-predominant cell loss (>50 percent) with sparing of other regions.

It is typical for HS pathology to be bilateral, although one side is usually more predominantly involved [8]. Reorganization of neuronal networks in response to cell loss is likely to contribute significantly to epileptogenesis [9].

The pathogenesis of HS is not completely understood. While birth and developmental histories are usually normal, a history of febrile seizures in early childhood is common. A long duration of febrile seizures, in particular, appears to be associated with the an increased risk of TLE [10]. In some patients and families, genetic factors appear to influence both the development of febrile seizures and the later development of TLE [11,12]. A link between human herpes virus 6 (HHV-6) and HS has also been posited based on association studies as well as examination of epileptogenic tissue samples [13]. (See "Treatment and prognosis of febrile seizures", section on 'Subsequent temporal lobe epilepsy'.)

Some neuroimaging studies suggest that neurodevelopmental factors may contribute to the development of both febrile seizures and TLE [14]. In the smaller subset of patients with mesial TLE who first present as adults, it is possible that an autoimmune limbic encephalitis may be the underlying pathogenesis in some patients [15-17]. (See "Autoimmune (including paraneoplastic) encephalitis: Clinical features and diagnosis".)

Accumulating evidence from advanced neuroimaging studies suggest that the neurologic abnormalities in patients with HS extend beyond the temporal lobe and can involve both gray and white matter structures on the contralateral as well as ipsilateral side as well as the cerebellum [18-23]. Some studies have correlated the degree of extrahippocampal abnormalities with neuropsychiatric deficits [24,25].

Other structural causes — A variety of additional structural pathologies can be identified with modern neuroimaging techniques. Known causes of focal epilepsy include:

Central nervous system infections

Perinatal injury

Cortical dysplasias (see "Seizures and epilepsy in children: Classification, etiology, and clinical features", section on 'Neurodevelopmental lesions')

Neoplasms (see "Seizures in patients with primary and metastatic brain tumors")

Vascular malformations

Head trauma (see "Posttraumatic seizures and epilepsy")

Stroke (cerebral infarction, cerebral hemorrhage) (see "Overview of the management of epilepsy in adults", section on 'Poststroke seizures')

The neuroanatomic locus of seizure origin and demographic features can vary with the underlying etiology. As examples, cerebrovascular disease and neoplasms generally present in later life, while epilepsy resulting from perinatal injury presents in infancy or early childhood. Epilepsy associated with cortical dysplasias presents at a mean age of 7 years (range <1 to 26 years) [26,27]. Post-traumatic epilepsy has a peak incidence in early adulthood and most commonly arises from the frontal and temporal lobes. (See "Posttraumatic seizures and epilepsy".)

Genetic focal epilepsy syndromes — There are several epilepsy syndromes involving focal epilepsy primarily arising from the frontal or temporal lobes. The majority of these syndromes are familial, although sporadic cases are also described.

Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE), also called sleep-related hypermotor epilepsy (SHE), is a genetically heterogeneous syndrome manifesting in childhood or adolescence with clusters of brief nocturnal seizures arising in non-rapid eye movement sleep [28-35]. Structural and unknown etiologies of SHE also exist, and seizures sometimes localize to the temporal lobe or other areas. Cognition and other neurologic functions are usually normal, and interictal electroencephalogram (EEG) is often normal. The course is usually benign with easily controlled seizures; however, one-third will develop drug resistance. (See "Sleep-related epilepsy syndromes", section on 'Sleep-related focal epilepsies'.)

Autosomal dominant lateral temporal epilepsy (ADLTE), also called autosomal dominant epilepsy with auditory features, or familial lateral temporal lobe epilepsy, is a genetically heterogeneous syndrome, associated with prominent auditory hallucinations and focal seizures that evolve into bilateral convulsive seizures [32,36-48]. Magnetic resonance imaging (MRI) is usually normal as is the interictal EEG. Seizures are easily controlled in most cases.

A number of familial temporal lobe epilepsies have been described [32,49-51]. In general, these are autosomal dominantly inherited but are otherwise genetically heterogeneous. They are variably associated with antecedent febrile seizures and hippocampal sclerosis [52-55]. The prognosis also varies between disorders; in general, those with hippocampal sclerosis are more likely to have refractory seizures [56,57].

The genetic basis of these syndromes is increasingly understood and appears to overlap significantly with that of cortical dysplasia and other neurodevelopmental lesions. (See "Seizures and epilepsy in children: Classification, etiology, and clinical features", section on 'Neurodevelopmental lesions'.)

The most commonly involved pathway described to date is the mechanistic target of rapamycin complex 1 (mTORC1) pathway. Causative mutations in DEPDC5, NPRL2, and NPRL3, which encode three subunits of the GATOR1 complex that regulates mTORC1 signalling, have been identified in multiple patients and families with focal epilepsy, often with overlapping phenotypes and in some cases in association with brain malformations [58-61]. Among these, DEPDC5 mutations appear to be the most common, accounting for approximately 10 percent of familial focal epilepsy cases in various cohorts [58,60,61]. Additional genetic causes of focal epilepsy include mutations in CHRNA2, CHRNA4, CHRNB2, KCNT1, and LGI1 [62-64].

The role of genetic testing in most patients with epilepsy is not yet established, and testing is often expensive. The clinical utility of extensive testing remains relatively limited except in children with severe epileptic encephalopathy; in such cases, when a causative mutation is identified, the etiology is understood and further testing may be avoided [65,66]. Further information regarding genetic testing for these disorders is available at https://www.ncbi.nlm.nih.gov/gtr/. Counseling for genetic testing is discussed separately. (See "Genetic testing".)

Benign focal epilepsies of childhood — Benign focal epilepsies of childhood are of unknown cause but may have a genetic component. Syndromes include:

Benign childhood epilepsy with centrotemporal spikes (BECTS) or benign rolandic epilepsy

Benign occipital epilepsy of childhood

Panayiotopoulos syndrome

These disorders are discussed separately. (See "Benign (self-limited) focal epilepsies of childhood".)

Unknown — In approximately 25 percent of patients with focal epilepsy, no cause is identified. In the absence of other neurologic abnormalities or a family history, such cases are considered to be of unknown cause (previously referred to as cryptogenic). In many patients with normal MRI who undergo epilepsy surgery, focal pathologies such as dysplastic lesions, microgyria, and gliosis are identified histopathologically [67].

CLINICAL FEATURES — Focal epilepsies are usually divided into mesiotemporal and neocortical based on electroclinical semiology. The most common focal epilepsy in adolescents and adults is temporal lobe epilepsy, while extratemporal or neocortical epilepsy is more common in young children.

Seizure types — Seizure types that can be seen with focal epilepsy include [2]:

Focal aware seizures

Focal impaired awareness seizures

Focal motor seizures

Focal nonmotor seizures

Focal to bilateral tonic-clonic seizures

Mesial temporal lobe epilepsy — Temporal lobe epilepsy (TLE) is the most common of the focal epilepsies. Most cases of TLE can be further localized to the mesial temporal lobe (hippocampus, amygdala, and parahippocampal gyrus).

Hippocampal sclerosis (HS) is the most common underlying cause of mesial TLE and the most common pathologic finding in patients undergoing surgery for mesial temporal lobe epilepsy. Central nervous system (CNS) infection (eg, encephalitis), head trauma, hamartomas, glial tumors, limbic encephalitis, vascular and congenital malformations, and perinatal injury are other causes [16,68]. (See 'Hippocampal sclerosis' above and 'Other structural causes' above.)

Seizure semiology — Focal seizures with impairment of consciousness or awareness (previously referred to as complex partial seizures) are the most common manifestation of mesial TLE [8]. Approximately one-third of patients also have focal seizures evolving to bilateral convulsive seizures (also referred to as secondary generalized seizures). Only a few patients with mesial TLE develop status epilepticus. Distinctive characteristics of mesial TLE seizures include the following:

An "aura" (a focal seizure with sensory or psychic symptoms) occurs in most patients. Common features include a rising epigastric sensation (often likened to a "roller coaster" sensation), and psychic or experiential phenomena, such as déjà vu, jamais vu, or fear (table 2). Auras of taste (gustatory hallucinations) and smell (olfactory hallucinations) are less common. Auras can occur in isolation or can precede a focal seizure with impairment of consciousness or awareness. In either case, patients with mesial TLE usually recall the seizure aura.

Focal seizures with impairment of consciousness or awareness (also called focal dyscognitive or complex partial seizures) usually manifest with a behavioral arrest and staring and last between 30 and 120 seconds. The patients are generally unaware and unresponsive during this period. Occasionally, such patients present with amnestic attacks, but more detailed questioning or observation of the seizures reveal the presence of olfactory hallucinations, other seizure auras, or ictal automatisms [69].

Automatisms are common, occurring in approximately 60 percent of focal seizures with impairment of consciousness in patients with mesial TLE [8,70,71]. These are repetitive, stereotyped, purposeless movements. In TLE, they are typically mild, involving the hands (picking, fidgeting, fumbling) and mouth (chewing, lip smacking).

Gelastic seizures are defined as focal seizures with uncontrollable stereotyped laughter (with or without a sensation of mirth). They are classically associated with hypothalamic hamartomas but can also arise from the temporal lobe, as proven by seizure freedom after resection [72], and from other locations in either hemisphere [73]. Thus, the gelastic component can be seen in many types of focal epilepsies and is not a reliable localizing or lateralizing feature.

Lateralizing features can occur during or after a focal seizure. Unilateral automatisms are usually ipsilateral to the seizure focus, while dystonic posturing almost invariably occurs on the contralateral side. Head deviation at seizure onset is usually ipsilateral to the seizure; when it occurs later, it is contralateral [74]. This later head turning also has a more forceful, involuntary appearance and is so-characterized as "versive." Contralateral clonic activity is relatively unusual. Lateralizing findings in the setting of mesial temporal sclerosis should be interpreted with some caution, as many of these patients have bilateral, independent seizure foci.

Less commonly observed behaviors associated with a temporal lobe seizure include ictal speech and vocalizations, affective behaviors (laughing, crying or fear), hypermotor behaviors usually associated with frontal lobe seizures, and so-called "leaving behavior" (walking or running away) [75-78].

Postictal confusion usually resolves within minutes. If postictal psychosis occurs, it typically lasts for days to weeks and often does not begin immediately after the seizure [79,80]. Postictal hemiparesis can occur contralateral to the seizure focus, and postictal aphasia can occur with a seizure emanating from the dominant hemisphere (see "Evaluation and management of the first seizure in adults", section on 'Postictal period'). Nose-wiping, performed by the hand ipsilateral to the focus of seizure onset, is a common postictal event in mesial TLE. Postictal wandering is not specific to TLE, but is seen more often with temporal compared with extratemporal seizures [81].

Heart rate changes commonly accompany temporal lobe seizures. In one report, abrupt tachycardia was present in the majority of both right and left-sided mesial temporal lobe seizures (29 out of 29 right-sided seizures and 42 out of 48 left-sided seizures), but the onset of tachycardia in relation to the ictal electroencephalogram (EEG) onset was earlier in right-sided seizures, often preceding the ictus [82]. One potential explanation is that the delayed heart rate increase associated with left mesial temporal lobe seizures results from seizure propagation to the right temporal lobe. Although some reports have noted that tachycardia is more typical of seizures originating from the right mesial temporal lobe and bradycardia is more common with left-sided seizures, most have not found this to be a useful lateralizing feature. Ictal bradycardia is much less common than tachycardia and in at least one study was associated with bilateral temporal lobe seizure activity [83].

Neuropsychiatric symptoms — The association between mesial temporal lobe epilepsy and neuropsychiatric symptoms is somewhat controversial [8,84-86]. Associated impairments of memory and cognition are often reported, but these may also result from frequent seizures and medication side effects [87,88]. While more severe abnormalities in cognition have been correlated with more severe and bilateral abnormalities on magnetic resonance imaging (MRI), this may represent confounding bias, rather than cause and effect [16,89,90]. Similarly, a cause and effect association between mesial temporal lobe epilepsy and depression, anxiety, and other psychiatric comorbidities is difficult to elucidate, although comorbidity is common [91].

Clinical course — Seizures associated with mesial temporal lobe epilepsy most commonly begin by adolescence, although there is a wide range. Over 80 percent of cases of TLE associated with HS manifest before the age of 16 years, but cases presenting in infancy and up to age 32 years have been reported [8,92]. Up to one-fifth of nonlesional cases may be familial [55].

Clinically, mesial TLE with hippocampal sclerosis is a progressive disorder. Seizures, initially controlled with antiseizure medications, can reemerge and become medically intractable in up to 60 to 90 percent of patients [8]. A younger age of onset and a history of febrile seizures were associated with a risk of intractability in one longitudinal series [93].

Longitudinal neuroimaging studies have demonstrated progressive neocortical atrophy in patients with drug-resistant TLE [94-96]. Timely surgical evaluation is an important component of the care of patients with drug-resistant TLE. (See "Surgical treatment of epilepsy in adults".)

EEG findings — The interictal EEG, when abnormal, typically shows epileptiform sharp waves over the temporal region. These are typically maximum at anterior or mid temporal electrodes (F7/F8, T1/T2, T3/T4) (waveform 1). With repeated studies or prolonged monitoring, the yield of interictal EEG in mesial TLE is over 90 percent [97]. Bitemporal independent discharges are observed in 30 to 40 percent of patients with mesial TLE [97,98]. Temporal intermittent rhythmic delta activity (TIRDA) is observed in as many as 25 to 40 percent of patients being evaluated for temporal lobe resection [99,100].

The ictal EEG shows relatively well-defined rhythmic and evolving discharges with a characteristic buildup, with a usual frequency in the theta range (waveform 2). Lateralized postictal slowing is often observed [97]. While the typical well-formed rhythmic theta ictal pattern is relatively specific for mesiotemporal epilepsy, it can also be seen in neocortical and extratemporal epilepsy; therefore, EEG patterns should be interpreted within the entire clinical context [101].

Neuroimaging — The most common magnetic resonance imaging (MRI) findings in patients with mesial TLE due to hippocampal sclerosis are hippocampal atrophy and increased T2 signal within the hippocampus (image 1 and image 2). Such findings are best seen on high-resolution, thin (<1.5 mm) coronal slices through the hippocampus [102-105]. Signal change without atrophy is a relatively nonspecific finding and may be seen in up to 30 percent of normal controls [106]. Bilateral MRI abnormalities are visualized in approximately 20 percent of patients [107]. Adult patients without TLE, but with a history of febrile seizures in childhood, are sometimes found to demonstrate similar MRI findings [108]. (See "Neuroimaging in the evaluation of seizures and epilepsy", section on 'Magnetic resonance imaging'.)

Other structural causes of mesial temporal lobe epilepsy, such as tumors, stroke, and vascular malformations, are well visualized on high-resolution brain MRI. Vascular malformations may be particularly prominent on gradient echo sequences, which are sensitive for blood products. In patients with focal cortical dysplasia, MRI findings may be subtle and include mild cortical thickening, a prominent deep sulcus, a cortical signal intensity change, or aberrant cortical architecture (image 3). (See "Overview of the clinical features and diagnosis of brain tumors in adults", section on 'Neuroimaging features' and "Vascular malformations of the central nervous system", section on 'Neuroimaging'.)

Functional and metabolic imaging techniques, including positron emission tomography (PET), single photon emission computed tomography (SPECT) and functional MRI are often used in the context of a surgical evaluation to help localize and lateralize mesial temporal lobe seizures. (See "Surgical treatment of epilepsy in adults", section on 'FDG-PET' and "Surgical treatment of epilepsy in adults", section on 'Ictal SPECT' and "Surgical treatment of epilepsy in adults", section on 'Speech and language localization'.)

Neocortical epilepsy — Neocortical epilepsy refers to extrahippocampal temporal lobe seizure disorders as well as those arising from outside the temporal lobe. Seizures may be focal with or without impairment of consciousness and may evolve into bilateral convulsive seizures. Symptoms depend on the area of cortex affected.

Neocortical temporal lobe epilepsy — Seizures arising from the temporal neocortex are relatively uncommon in relation to mesial temporal lobe seizures and are less well characterized. In addition to the rare familial syndrome autosomal dominant focal epilepsy with auditory features, neocortical TLE is associated with other structural abnormalities occurring in this area, including vascular malformations, neoplasms, and traumatic brain injury. (See 'Other structural causes' above.)

With the close proximity and extensive reciprocal connections between the hippocampus and temporal neocortex, it is not surprising that the clinical syndromes of mesial TLE and neocortical TLE overlap substantially, such that they cannot reliably be distinguished by their clinical characteristics. However, auras that include auditory hallucinations or distortions, vertigo, or complex visual hallucinations and do not include epigastric phenomena suggest a focus arising from the temporal neocortex rather than the hippocampus. Automatisms are less common in neocortical than mesial TLE.

Interictal and ictal EEG features do not reliably distinguish mesial TLE and neocortical TLE, although in the latter, one may see more predominant discharges at lateral or posterior temporal electrodes in the interictal recording.

Frontal lobe epilepsy — Frontal lobe epilepsy makes up approximately 30 percent of patients undergoing epilepsy surgery. Causes include trauma, neoplasia, vascular malformations, encephalitis, and cortical dysplasia, as well as genetic syndromes and those with an unknown cause [28,67,109-111]. (See 'Etiologies' above.)

Reflecting the large area of the frontal cortex and its diverse functions, frontal lobe epilepsy can manifest in many forms. Seizure manifestations generally reflect the area of cortex involved, which is not necessarily the site of origin of the seizure. As an example, among four patients with supplementary motor area (SMA) seizures undergoing epilepsy surgery, only one had an epileptic focus in the SMA [109]. Seizures arising from the orbitofrontal cortex that secondarily involve the adjacent mesial temporal lobe can be indistinguishable from mesial TLE [67,110].

Common characteristics of frontal lobe seizures are short duration (<30 seconds) and predilection for occurrence during sleep [34,67,112,113]. The latter is particularly true for frontal lobe focal seizures with impairment of consciousness (complex partial seizures) and supplementary motor seizures. Differentiating nocturnal seizures from parasomnias can be challenging, and it is not uncommon for the two to co-exist [114]. (See "Sleep-related epilepsy syndromes", section on 'Sleep-related hypermotor epilepsy (SHE)' and "Disorders of arousal from non-rapid eye movement sleep in adults".)

Seizure clusters and status epilepticus (whether focal or generalized) are also more common in frontal lobe epilepsy than with TLE. A postictal state may be brief or absent (see "Evaluation and management of the first seizure in adults", section on 'Postictal period'). Evolution of frontal lobe seizures into bilateral convulsions (secondary generalization) was at one time thought to be more common than in mesial TLE, but systematic comparisons suggests that this has a similar incidence in both [67,110,112].

Frontal lobe seizure types include:

Focal seizures with impairment of consciousness or awareness (also called focal dyscognitive or complex partial seizures) are often characterized by hypermotor behaviors (proximal limbs, tonic) [113,115]. These can produce bizarre-looking episodes that may be mistaken for psychogenic nonepileptic seizures. (See "Psychogenic nonepileptic seizures: Etiology, clinical features, and diagnosis", section on 'Differential diagnosis'.)

Other features that suggest focal seizures of frontal rather than temporal lobe origin include bicycling automatisms as well as pelvic thrusting and other sexual automatisms (table 2). Tonic posturing and head and eye deviation (version), usually contralateral to the side of the seizure focus, can occur in some patients [74]. Vocalizations are also very common.

While seizure auras are common in frontal lobe epilepsy, they are less ubiquitous than in mesial TLE, and the sensation is often ill-described and typically does not include epigastric phenomenon. Fear and anxiety occur as seizure auras in both TLE and frontal lobe epilepsy [67,112,116,117].

Consciousness may be more preserved in frontal lobe focal seizures compared with TLE [67]. Patients often report recall of ictal events even though they are not able to respond, but the accuracy of this reporting is not certain.

Focal motor seizures involving the primary motor cortex will produce hemiclonic activity in the contralateral face, arm, or leg. Seizures may be quite focal (isolated to one limb or face) or may spread (or march) to adjacent areas (ie, Jacksonian seizure). Hemiclonic activity is more common in complex partial seizures of frontal origin than with those in TLE.

Supplementary motor area seizures typically produce stereotyped asymmetric tonic movements. One example is the "fencing posture," in which the head and eye deviate to the contralateral side, with extension of the contralateral arm and flexion of the ipsilateral arm. The most prominent tonic activity occurs contralateral to the seizure focus. Brief superimposed clonic movements or vocalizations may also occur. Speech arrest may accompany seizures arising from the dominant hemisphere. There may be a somatosensory aura. Despite bilateral tonic movements, consciousness is often preserved unless there is secondary generalization.

So-called frontal absence seizures manifest with staring, trance-like states. These seizures originate from the frontopolar or medial frontal regions [28]. These seizures are more prolonged than other seizure types, often lasting several minutes, sometimes hours, or even days [67].

Evolution to a bilateral convulsive seizure (secondary generalization) may occur after any of the above initial ictal manifestations. A minority of patients have generalized seizures that occur without preceding dyscognitive or motor symptoms [110].

Various subgroups of patients with frontal lobe and insulo-opercular seizures can be identified based on semiology [118,119]. These subgroups may be useful to guide preoperative localization and intracranial (stereotactic) EEG implantation strategies in patients considered for epilepsy surgery.

Both ictal and interictal EEG can be misleading in frontal lobe epilepsy with normal or nonspecific abnormal findings. An initial standard outpatient EEG detects interictal epileptiform abnormalities in 29 to 55 percent of patients (waveform 3) [28]. The yield of abnormal findings increases with repeated and prolonged monitoring.

Ictal EEG patterns can include voltage attenuation, electrodecremental response, rhythmic alpha or theta activity, and spike or spike and wave discharges. Up to one-third of patients do not have a diagnostic ictal EEG during a frontal lobe seizure. Large areas of the frontal lobe are inaccessible to surface EEG or can be obscured by prominent motor activity. The use of transverse montages may be helpful to record seizure activity over the vertex. Another problem is that rapid spread of the seizure can lead to false localization and even lateralization of the seizure focus. In some cases, rapid spread of frontal discharges mimics primary generalized spike-wave complexes. This is referred to as "secondary bilateral synchrony," with interictal epileptiform discharges that appear to be primarily generalized but are actually secondarily generalized focal discharges. Frontal lobe absences are associated with an irregular spike-wave pattern.

Because of these challenges, additional functional and metabolic imaging and invasive EEG monitoring is usually required in patients undergoing surgical evaluation in order to adequately localize frontal seizures, particularly when structural MR imaging is normal. (See "Surgical treatment of epilepsy in adults", section on 'Seizure localization'.)

Occipital lobe epilepsy — Occipital lobe epilepsy is uncommon. Seizures arise from the occipital cortex in 2 to 8 percent of patients in surgical case series [120]. Tumors, vascular malformations, and developmental abnormalities are the most commonly identified abnormalities on MRI [121]. Occipital lobe seizures also occur as a benign focal epilepsy of childhood. (See "Benign (self-limited) focal epilepsies of childhood", section on 'Benign childhood epilepsy with occipital spikes'.)

Visual phenomena occur as a seizure aura in approximately 80 percent of patients. Phenomena vary from unformed images, such as flashing or steady white or colored lights, to very complex visual hallucinations (see "Approach to the patient with visual hallucinations", section on 'Seizures'). Visual distortions also can occur, including those of size (macropsia, micropsia), shape (metamorphopsia), and color (dyschromatopsia) [122]. The visual aura usually manifests in the contralateral visual field, but may be described as bilateral [120]. Ictal blindness also is described [123]. Occipital seizure auras also can include experiential, abdominal, and somatosensory phenomena.

Focal seizures with impairment of consciousness and evolution to bilateral convulsions (secondary generalization) occur in approximately equal proportion in occipital lobe epilepsy [120]. In the former, motor automatisms, head deviation, and focal motor seizure activity are often described. Postictal blindness in one or both hemifields occurs in some patients.

In occipital lobe epilepsy, the interictal EEG shows localizing spike focus in 50 to 80 percent of patients [120,121,123]. The ictal EEG is less often localizing, usually because of rapid seizure spread.

Parietal lobe epilepsy — Seizures arising from the parietal lobe are uncommon and poorly characterized. Small case series suggest that such patients do not have a distinguishing clinical syndrome. Lateralized somatosensory auras (tingling and numbness) can occur but are neither specific nor sensitive features; anxiety and experiential phenomena have been described as well [124-126]. Ictal phenomena can include asymmetrical tonic or clonic activity as well as focal seizures with altered consciousness and automatisms, resembling TLE [125-127]. Todd paralysis can occur as a postictal phenomenon. (See "Evaluation and management of the first seizure in adults", section on 'Postictal period'.)

Both ictal and interictal EEG are unreliable in localizing seizures of parietal lobe origin [125,127]. In surgically treated patients, underlying pathologies have included tumor, vascular malformation, and nonspecific gliosis.

Hemispheric syndromes — Hemispheric syndromes are focal (localization-related) and neocortical, but the epileptogenic zone is so widespread as to involve nearly an entire hemisphere. In most cases, structural abnormalities are identified on MRI. EEG abnormalities include multifocal or widespread discharges lateralized to one hemisphere, along with amplitude asymmetry, lateralized or focal slowing, and background slowing. Hemiparesis, hemianopia, and developmental delay often coexist.

These hemispheric syndromes are often difficult to treat, even with multiple antiseizure medications. In the most refractory cases, functional hemispherectomy can be very effective. (See "Seizures and epilepsy in children: Initial treatment and monitoring" and "Overview of the management of epilepsy in adults".)

Causes include perinatal infarction, hemimegalencephaly, Rasmussen syndrome, and Sturge-Weber syndrome.

Perinatal infarction is probably the most common cause of hemispheric epilepsy. Most infants have acute symptomatic seizures as the initial presenting symptom. The prognosis is determined by the extent of injury; approximately one-third of patients develop epilepsy [128]. Seizure types vary and include focal and secondarily generalized seizures. (See "Stroke in the newborn: Classification, manifestations, and diagnosis".)

Hemimegalencephaly is an extreme form of unilateral cortical dysgenesis, with hamartoma formation. It is not linked to any stage in brain development and can be an isolated finding or occur as part of tuberous sclerosis, Klippel-Trenaunay, or other neurocutaneous syndromes [129,130]. Seizures usually begin within the first six months of life. Focal seizures evolving to bilateral convulsive seizures are most common, and epileptic spasms and tonic seizures also can occur. The baseline EEG is usually very abnormal, often showing hypsarhythmia or a burst suppression pattern. The MRI appearance of unilaterally thickened cortex with flattened gyri, asymmetric ventricular size, and displacement of midline structures is usually diagnostic.

Rasmussen encephalitis is a rare inflammatory disorder of uncertain, probably immune-mediated, pathogenesis that affects one cerebral hemisphere [131-133]. Patients typically present between 14 months and 14 years of age with seizures, progressive hemiparesis, and unilateral cerebral atrophy on MRI [134,135]. Seizures are unilateral and intractable, frequently evolving into focal motor status epilepticus ("epilepsia partialis continua"). MRI may show mild signal intensity change in the cortex and the white matter. Neuropathology shows inflammation. Immunosuppressive treatments are generally unsuccessful. Hemispherectomy is the most common surgical approach. (See "Seizures and epilepsy in children: Refractory seizures", section on 'Hemispherectomy'.)

Sturge-Weber syndrome (encephalo-trigeminal angiomatosis) is associated with leptomeningeal angiomatosis, caused in most cases by mosaic mutations in the GNAQ gene [136]. Seizures begin in the first year of life in 75 percent of individuals, and by year 5 in 95 percent [137]. Patients have facial angioma, cortical atrophy, gyriform calcifications, and contralateral hemiparesis and hemianopia. Focal seizures evolving to bilateral convulsive seizures are the most common seizure type. On EEG, in addition to epileptiform discharges and slowing on the side of the angiomatosis, low-amplitude or absent background may be seen. (See "Sturge-Weber syndrome".)

DIAGNOSTIC EVALUATION — Most patients with new-onset seizures require electroencephalography (EEG) and neuroimaging (magnetic resonance imaging [MRI]) to characterize the seizure type and cause. This is discussed in detail separately. (See "Evaluation and management of the first seizure in adults" and "Electroencephalography (EEG) in the diagnosis of seizures and epilepsy" and "Neuroimaging in the evaluation of seizures and epilepsy", section on 'Magnetic resonance imaging'.)

Semiologic seizure classification attempts to associate clinical features of the seizures with the neuroanatomic focus of seizure origin. However, localization based on either clinical or EEG features alone is often inaccurate. This may be because seizures arise from a part of the brain that is either clinically silent or inaccessible to scalp EEG recordings. Also, seizure activity often spreads quickly from one brain region to another and obscures the original focus of seizure origin [138]. As a result, clinical symptoms and EEG activity may reflect regional brain involvement, but not necessarily the primary neuroanatomic site of origin [139-142].

Similarly, it is not always possible to distinguish focal from primary generalized seizures on clinical and historical information alone [143]. A seizure aura suggests a focal onset. While patients with generalized seizures sometimes report nonspecific symptoms that may suggest a seizure aura, highly specific sensory symptoms, such as olfactory auras, are highly diagnostic of focal epilepsy [144]. In one series, both aura and longer seizure duration suggested focal seizures, while ictal eye blinking and higher seizure frequency suggested primary generalized epilepsy [145]. No clinical feature was absolute.

The interictal EEG may be normal in patients with focal epilepsy. When abnormal, it shows focal spikes or sharp waves. The ictal EEG (if recorded) usually shows a focal or regional discharge at onset. With a normal interictal EEG, the diagnosis of focal epilepsy is based on clinical symptoms. While EEG is an important diagnostic test in evaluating a patient with possible epilepsy, there are several reasons why EEG alone cannot be used to make or refute a specific diagnosis of epilepsy. This topic is discussed in detail separately. (See "Electroencephalography (EEG) in the diagnosis of seizures and epilepsy".)

DIFFERENTIAL DIAGNOSIS — The symptoms of focal seizures can be difficult to distinguish from nonepileptic paroxysmal conditions, including movement disorders, migraine, sleep disorders, and psychiatric conditions. In our experience, the misdiagnosis of seizures is common. Up to one-third of patients seen at epilepsy centers for difficult "seizures" have been misdiagnosed, sometimes because of over-interpretation of benign EEG variants as abnormal. The most common conditions misdiagnosed as seizures are psychogenic nonepileptic seizures and syncope. Prolonged EEG monitoring can be useful when the diagnosis is uncertain. (See "Nonepileptic paroxysmal disorders in adolescents and adults" and "Video and ambulatory EEG monitoring in the diagnosis of seizures and epilepsy".)

SUMMARY AND RECOMMENDATIONS

Etiology – Focal epilepsy, also known as localization-related or partial epilepsy, arises as a consequence of focal brain pathology or as a part of a syndrome of genetic or unknown cause. (See 'Introduction' above and 'Etiologies' above.)

Hippocampal sclerosis (also called mesial temporal sclerosis) is the most commonly identified pathological correlate of temporal lobe epilepsy (TLE), itself the most common localization of focal epilepsy. Febrile seizures, particularly prolonged and complex febrile seizures, are a risk factor for hippocampal sclerosis. TLE associated with hippocampal sclerosis typically presents in childhood or early adolescence. While initially responsive to antiseizure medication treatment in most cases, seizures can become medically intractable. (See 'Hippocampal sclerosis' above.)

Other structural causes of symptomatic focal epilepsy include acquired brain injury, neoplasm, or focal developmental anomalies. (See 'Other structural causes' above.)

Several epilepsy syndromes involve focal epilepsy primarily arising from the frontal or temporal lobes; most of these syndromes are familial. (See 'Genetic focal epilepsy syndromes' above.)

Clinical features

Seizure types that may be seen with focal epilepsy include the following (see 'Seizure types' above):

-Focal aware seizures

-Focal impaired awareness seizures

-Focal motor seizures

-Focal nonmotor seizures

-Focal to bilateral tonic-clonic seizures

Temporal lobe epilepsy (TLE) is the most common of the focal epilepsies; focal seizures with impaired consciousness or awareness are the most common manifestation of mesial TLE. Seizures associated with mesial temporal lobe epilepsy most commonly begin by adolescence, although there is a wide range. (See 'Mesial temporal lobe epilepsy' above.)

Neocortical epilepsy refers to extrahippocampal temporal lobe seizures as well as those arising from the frontal, occipital, or parietal lobes. Seizures may be focal with or without impaired awareness and may evolve into bilateral convulsive seizures. Symptoms depend on the area of cortex affected (table 2). (See 'Neocortical epilepsy' above.)

Hemispheric syndromes are focal and neocortical, but the epileptogenic zone is so widespread as to involve nearly an entire hemisphere. (See 'Hemispheric syndromes' above.)

Evaluation – Certain clinical features of the seizure can suggest a specific focal epileptic syndrome, and electroencephalography (EEG) findings also help localize the focus of seizure onset. Most patients also require neuroimaging with magnetic resonance imaging (MRI) to evaluate the seizure type and cause. (See "Neuroimaging in the evaluation of seizures and epilepsy" and "Electroencephalography (EEG) in the diagnosis of seizures and epilepsy" and "Video and ambulatory EEG monitoring in the diagnosis of seizures and epilepsy".)

Management – The management of focal epilepsy and other epilepsy syndromes is discussed separately. (See "Overview of the management of epilepsy in adults" and "Initial treatment of epilepsy in adults" and "Evaluation and management of drug-resistant epilepsy" and "Surgical treatment of epilepsy in adults" and "Seizures and epilepsy in children: Initial treatment and monitoring".)

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Topic 2231 Version 43.0

References

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