Chapter 54 Focal and Multifocal Seizures

Introduction

Focal or partial seizures originate in one region of the brain, where they may stay confined or spread to other areas. Multifocal seizures arise from multiple locations and constitute an important type of seizure in infancy and childhood. Both focal and multifocal types have been under-recognized in children, but modern epidemiologic studies show that focal epilepsies account for about 60 percent of all seizure disorders [Berg et al., 1999a,b; Sillanpaa et al., 1999]. The behavioral manifestations of focal seizures relate not only to the region of the brain involved during the ictal discharge, but also to the maturation of the nervous system and the integrity of the pathways necessary for clinical expression.

Focal seizures in the very young are subtler and less declarative than focal seizures seen later in life [Acharya et al., 1997; Hamer et al., 1999; Nordli et al., 1997]. This is particularly true in infants and children with diffuse encephalopathies, in whom brain immaturity, diffuse cerebral dysfunction, or both make manifestations of focal seizures difficult to recognize. Focal seizures also can be mistaken in older children when the presence of secondary convulsive movements prompts casual observers to label the event a “generalized tonic-clonic” seizure. With this misdiagnosis, critical elements of the seizures are overlooked. As described later, careful consideration of the unique features present in pediatric focal seizures can improve diagnostic accuracy.

In a majority of children with focal seizures, no focal structural lesion is present, and the seizures either are the expression of an idiopathic disorder (benign rolandic epilepsy) or are cryptogenic. This finding is in contrast to adults, in whom a focal seizure strongly implies the presence of a focal structural lesion (e.g., stroke, brain tumor). Instead, only 10 percent of children with focal seizures have brain tumors or strokes. In one large epidemiologic study, only 4 of 613 children with epilepsy had a brain tumor [Berg et al., 2000a].

The prognostic value of seizure classification by itself is limited, and a fuller understanding of the patient is achieved by making an epilepsy syndrome diagnosis. As pointed out in Chapter 50, two children with the same seizure type can have markedly different outcomes. Establishing an epilepsy syndrome diagnosis is the best way to determine on management options for different patients. An epilepsy syndrome diagnosis is preferred for assessing prognosis and treatment. Although it may not be possible to diagnose every child immediately on presentation, prospective population-based studies suggest that most children can ultimately be diagnosed with an epilepsy syndrome. Many factors contribute to the diagnosis of a syndrome, but in practice, three are most important:

1. age and development of the patient

2. type or types of observed seizures

3. interictal electroencephalogram (EEG) features.

Many well-known epilepsy syndromes are delineated by specific clinical triads comprising these factors. Accordingly, this chapter includes a discussion of epilepsy syndromes that frequently manifest with focal or multifocal seizures.

Children with multifocal seizures (three or more foci, involving both hemispheres) may have unfavorable forms of epilepsy (e.g., migrating partial seizures, Dravet’s syndrome, symptomatic diffuse epileptogenic encephalopathies not otherwise specified). Although these epilepsies manifest with focal seizures, the children usually have evidence of concomitant diffuse cerebral dysfunction on clinical examination, developmental history, and interictal EEG studies. Correct diagnosis is particularly challenging in the group of children with focal seizures and evidence of widespread, diffuse, or multifocal cerebral dysfunction; too often, these patients end up in broad, poorly descriptive “wastebasket” categories, such as Lennox–Gastaut syndrome or generalized symptomatic epilepsy not otherwise specified. Lennox–Gastaut syndrome has particular diagnostic features and is not synonymous with diffuse symptomatic epilepsy, as discussed in Chapter 53. In summary, the importance of correctly recognizing focal seizures cannot be overstated.

Recognition of Focal Seizures in Children

Clinical features alone cannot always allow one to diagnose a focal seizure correctly. Rather, “focal seizure” is actually an electroclinical diagnosis. It usually is made following consideration of multiple factors related to the patient and the clinical event, but may require EEG confirmation, particularly in the very young. Still, a number of important clues can help point to the presence of focal seizures in children (Box 54-1). Experience using video EEG monitoring suggests that certain clinical features tend to have focal ictal EEG correlates [Nordli et al., 2001] (Figure 54-1).

Fig. 54-1 Typical interictal findings on electroencephalogram (EEG) in children with focal seizures.

A, This EEG from a child with benign rolandic epilepsy of childhood (BREC) shows focal stereotypic spikes appearing on a normal background. Notice that each spike closely resembles the others in morphology and location, as is typical of idiopathic localization-related epilepsies. B, By contrast, this EEG from a child with an epileptogenic focal structural lesion in the left temporal region demonstrates pleomorphic spikes and background slowing in the same region. C, EEGs from children with multifocal seizures often show multifocal interictal epileptiform discharges.

Auras

Auras are special sensory or psychogenic phenomena that can be described only by the patient. They occur in a variety of forms and have important localizing value. Although the concurrent ictal EEG often does not reveal clear electrographic expression in most patients, auras are believed by most authorities to be the manifestation of discrete focal seizures. When a somatosensory aura is specific and an ictal EEG correlate is present, the ictal discharge is often low-voltage fast activity localized over the corresponding region of the sensory homunculus. Other auras arising from limbic structures often are “indescribable,” or may have a fearful quality or include a feeling of epigastric discomfort. These discharges arise from subcortical structures, so the EEG may reveal little to no change, other than ipsilateral diffuse delta activity or a rhythmic theta-alpha pattern in the anterior to midtemporal region, particularly when the onset of activity is mesial temporal in location. Auras are a very reliable indicator of a focal seizure.

Automatisms

Limb automatisms are semipurposeful movements such as the rubbing, fumbling, or picking that may be seen in focal seizures. Oral automatisms, such as lip smacking, can occur with generalized absence seizures, but unilateral limb automatisms suggest a focal process. Well-developed distal limb automatisms are rarely seen in infants but become more common above age 6 years. When unilateral, automatisms are another helpful sign, indicating the presence of a focal seizure.

Behavioral Arrest

In some infants and young children, the most conspicuous feature of a focal seizure may be the sudden, abrupt cessation of on-going activity or a marked change in demeanor, as indicated by subtle but distinct changes in facial expression. Parents easily identify these features because they represent a clear paroxysmal alteration in the child’s behavior. Parents are particularly well attuned to the nature of their child’s habitual behavior, but these behavioral changes may be challenging for a person unacquainted with the child to identify on video tape. In the preverbal child, or in many children with special needs, it is impossible to ascertain alteration of consciousness reliably. Alteration of consciousness cannot be unambiguously inferred from behavior (e.g., daydreaming in school). To assess consciousness accurately, test items must be given and recall tested after the seizure. In children, this often is not possible, so the simple description of a behavioral arrest is more reliably used, rather than trying to infer if a seizure was truly “complex partial.” Behavioral arrest seizures also have been described as hypomotor seizures. This description refers to a sudden reduction in the motor activity of the child. The electrographic ictal accompaniment often emanates from the temporal lobe or posterior quadrant and may be composed of monotonous rhythmic delta, rhythmic theta-alpha patterns with an electrographic “crescendo” appearance, or low-voltage fast discharges that subsequently evolve to other rhythms (Figure 54-2). In children above age 3 years, behavioral arrest may accompany both focal and generalized seizures (absence seizures), so in isolation it is not a reliable indicator of a focal seizure; however, since absence seizures rarely occur in children less than 2.5 years, it is likely to be the correlate of a focal seizure in this age group.

Fig. 54-2 Common infantile ictal patterns on electroencephalogram (EEG) in focal seizures.

A, EEG during a behavioral arrest seizure shows an ictal discharge in the left temporal region. Notice the rhythmic build-up of fast activity. Ictal discharges usually have an evolution in frequency, amplitude, and spatial distribution (like a crescendo in music). B, During a clonic seizure involving the left arm, the EEG demonstrates an ictal correlate consisting of repetitive spikes in the right central region. Notice that the ictal discharge remains very localized. C, EEG obtained during a versive seizure with eyes deviating to the right, or the same side as for the ictal discharge, shows a fast ictal pattern superimposed on some rhythmic slowing in the right posterior head region.

Dystonic Postures

A dystonic posture of a limb is a feature seen in focal seizures. It is infrequently seen in the very young but becomes more common in the school-age child. Dystonic postures of the hand are usually contralateral to the seizure focus. They may often be coupled with ipsilateral (to the seizure focus) limb automatisms. A unilateral dystonic posture suggests a focal seizure.

Focal Clonus

Hand or arm clonus (clonic seizure) is another reliable feature of focal epilepsy. This activity is easily recognized as ictal by the repetitive nature of the jerking, and the inability to suppress the motion by passive restraint. It usually is accompanied by runs of rhythmic spike discharges in the contralateral rolandic region, and is a reliable indicator of a focal seizure.

Spasms

Spasms can be recognized by their tendency to recur in clusters, many times in an almost periodic fashion, with a fairly constant interval between some of the individual spasms. Spasms have a quick or myoclonic component at the start, followed by a brief sustained posture (tonic phase), followed in turn by a relaxation. Spasms that are asymmetric, that occur in a child with hemiparesis or other focal pathology, or that are associated with marked interhemispheric asymmetries on EEG are most likely focal seizures. In about 25 percent of patients with spasms, clear electrographic focal seizures can be detected before, during, or after the cluster. The EEG accompaniment of spasms often contains diffuse electrodecrements, even if they are preceded by clear focal seizures [Kubota et al., 1999].

Tonic Postures

Tonic postures, both symmetric and asymmetric, are seen with focal seizures. It is surprising to observe how often symmetric tonic postures can occur as a manifestation of a focal seizure in infants, and also how unreliable asymmetries of tonic postures can be in localizing ictal onsets. It is possible that these tonic postures are generated in deeper brainstem or subcortical structures and are not direct manifestations of the ictal discharges. This finding would explain why some asymmetric tonic postures can be reversed by passive turning of the head during a seizure, in a fashion similar to the tonic neck reflex elicited in the newborn. As the child matures, symmetric tonic postures are seen less frequently as a manifestation of a focal epilepsy. Instead, tonic postures become more asymmetric and show more lateralizing features.

Version

Pronounced and sustained lateral version of the eyes (versive seizure) is rarely encountered as an ictal manifestation in infants or young children. When present, version is another indicator of a focal seizure. In contrast with older children and adults, in whom the electrographic discharge often is best developed in the contralateral frontotemporal region, the ictal discharge in infants is more often in the ipsilateral occipital lobe.

Seizure Classification: International League Against Epilepsy

The International League against Epilepsy (ILAE) Commission on Classification proposed a classification of seizures in 1981. This scheme was widely used for almost three decades. Recently, a new ILAE commission on classification proposed a substantial revision [Berg et al., 2010] (Box 54-2). Now, the term “focal” replaces the previous term “partial,” and the obligatory separation of partial seizures into simple, complex, and secondary generalized has been discarded. Focal seizures still may be described further, if desired. One such way is to identify the degree of impairment. These and other descriptive terms are outlined in a previously published glossary [Blume et al., 2001] (Box 54-3). Examples of descriptors listed in the 2010 report include “without impairment of consciousness or awareness,” “with impairment of consciousness or awareness,” and “evolving to bilateral convulsive seizure.” The reader will note that these terms roughly equate to the older terms of simple, complex, and secondary generalized seizures. The important distinction is that these terms are no longer required but may be used by those who wish to maintain continuity with the 1981 classification. This adjustment appears minor, but is very useful because it is often not possible to determine alteration of consciousness reliably in the very young or in those with difficulties with communication. Lüders and colleagues have a logical and simple system that has been used internationally in major epilepsy centers (Lüders et al., 1999]. Others have proposed a much-simplified semiologic classification system for use in the very young [Nordli et al., 1997]. Neither of these schemes has been endorsed by the ILAE [Nordli et al., 1997]. While seizures may sometimes be broadly classified using the most prominent and early feature of the seizure, the various combinations of features, patterns, and time course of the seizure cannot be adequately summarized in a single word or phrase. Nothing can replace a thorough and meticulous description of the seizure. Indeed, the historic narrative of the seizure, as described or observed by parents, is the single most helpful piece of information allowing proper diagnosis of the seizure disorder and should be recorded, as accurately as possible, with few or no editorial comments.

Box 54-3 Further Descriptions of Focal Seizures

Without impairment of consciousness or awareness

With observable motor or autonomic components: roughly corresponds to the concept of “simple partial seizure.” “Focal motor” and “autonomic” are terms that may adequately convey this concept, depending on the seizure manifestations

Involving subjective sensory or psychic phenomena only: corresponds to the concept of an “aura,” a term endorsed in the 2001 Glossary

With impairment of consciousness or awareness: roughly corresponds to the concept of “complex partial seizure.” “Dyscognitive” is a term that has been proposed for this concept [Blume et al., 2001]

Evolving to a bilateral, convulsive seizure (involving tonic, clonic, or tonic and clonic components): this expression replaces the term “secondarily generalized seizure”

Epilepsy Syndromes with Focal Seizures

The ILAE classification of epilepsy syndromes is reviewed in Chapter 50. A recent modification of the ILAE classification eliminated the “focal” and “generalized” headings, along with the previous terms “idiopathic” and “symptomatic” (Box 54-4) [Borg et al., 2010]. One way to organize the recognized syndromes is by the specificity of the diagnostic criteria, further organized by age.

Box 54-4 Electroclinical Syndromes Categorized by Age at Onset

Neonatal Period

Benign familial neonatal epilepsy (BFNE)

Early myoclonic encephalopathy (EME)

Ohtahara’s syndrome

Less Specific Age Relationship

Familial focal epilepsy with variable foci (childhood to adult)

Reflex epilepsies

Neonatal Period

Benign Familial Neonatal Epilepsy

Of the three recognized epilepsy syndromes in neonates, only one has prominent focal seizures: benign familial neonatal epilepsy (BFNE). The other two syndromes, early myoclonic encephalopathy (EME) and Ohtahara’s syndrome, may have accompanying focal seizures, but the predominant seizures are myoclonic, tonic, or epileptic spasms. BFNE was first described in 1964 by Rett and Teubel [Rett and Teubel, 1964]. Before the advent of newborn video-EEG recordings, it was thought that the seizures in this syndrome might be generalized, but subsequent recordings showed that the predominant seizures are focal clonic or adversive, even though the accompanying EEG may show diffuse flattening at the onset. Ronen et al., reported the incidence as 14.4 per 100,000 live births [Ronen et al., 1999]. The clinical features have been thoroughly reviewed by Plouin [Plouin, 2008]. Most seizures (80 percent) start on the second or third day of life in term, otherwise healthy, newborns. Clinically, they usually begin with a diffuse tonic component, followed by a variety of motor and autonomic phenomena. Motor manifestations may include prominent oculofacial features, limb clonus, or both. Interictal EEG backgrounds are usually normal or may show a théta pointu alternant pattern, which consists of short bursts of rhythmic theta activity with sharply contoured components. Ictal EEGs have shown initial flattening, which may be focal or diffuse, followed by subsequent ictal rhythms. Family history, by definition, is positive and the inheritance is autosomal-dominant. Mutations in the genes encoding KCNQ2 and KCNQ3 account for the majority of cases. There are no official guidelines for treatment of BFNE and it is uncertain whether treatment is beneficial in the long run. There are clear regional preferences but phenobarbital, sodium valproate, and phenytoin have all been used. The long-term outcome is favorable, although 11 percent of patients may have epilepsy later in life [Plouin, 2008].

Infancy

There are at least four well-recognized syndromes occurring in infancy that may present with focal or multifocal seizures. Some proposed syndromes have features that overlap very closely with others. If one takes a broad view and lumps some of these variants together, then there are two syndromes with favourable outcomes, and two that are usually quite severe. Benign infantile epilepsy and benign familial infantile epilepsy share many clinical features but differ with regard to the family history. Epilepsy of infancy with migrating focal seizures and Dravet’s syndrome are severe epilepsies with very different clinical features.

Benign Nonfamilial Infantile Seizures

Fukuyama in 1963 and later Watanabe were among the first to describe infants with the onset of epilepsy in the first 2 years of life with no known cause and excellent outcome [Fukuyama, 1963; Watanabe and Okumura, 2000]. Fukuyama originally described these seizures as generalized convulsions, but this was before the advent of modern video-EEG recordings and it is likely that these were actually focal seizures with secondary spread. Watanabe and colleagues described a case series in 1987 and noted clear focal features, describing these seizures as “complex partial” [Watanabe and Okumura, 2000]. Whether these are two separate conditions or one syndrome is a matter of some debate. In both cases, there is normal development before the onset of seizures. Imaging studies and metabolic tests are unremarkable. Onset is mostly within the first year of life in both cases. The interictal EEG is normal. In both cases, seizures may manifest with blank staring, and may be followed by secondary generalization in the Fukuyama type. Seizures may occur in clusters in both. The ictal focus is most often in the temporal region in the Watanabe form and in the centroparietal region in the Fukuyama type. Both demonstrate an excellent response to treatment and have normal development. Capovilla and colleagues have described another infantile epilepsy with excellent outcome. These infants have focal seizures and a characteristic interictal EEG finding of a “bell-shaped” discharge, which is maximal at the vertex [Capovilla and Vigevano, 2001]. Infants present between 8 and 30 months with relatively bland seizures characterized by motion arrest, some tonic stiffening, and oxygen desaturation. Seizures are infrequent and usually of short duration. The authors did not recommend treatment with antiepileptic drugs (AEDs) in most cases. A family history of epilepsy is present in half the cases and the outcome is very favorable.

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