Focal seizures are the most common seizure type presenting in childhood. They may present as the occurrence of a single seizure type, or as part of a wider spectrum of seizure types integral to an epilepsy syndrome. By definition and implication, such seizures arise from one area of the brain. The most recent proposal by the ILAE (The International League Against Epilepsy) defined a focal seizure “as one that originates within networks limited to one hemisphere. They may be discretely localised or more widely distributed and may also arise in subcortical structures. For each seizure type, ictal onset is consistent from one seizure to another, with preferential propagation patterns that can involve the contralateral hemisphere. In some cases however there is more than one network, and more than one seizure type, but each individual seizure type has a consistent site of onset.”¹

Focal seizures can then be described on the basis of semiology (the clinical presentation of the event), which depends on the area of brain origin and propagation pattern, both of which define the localization of seizure onset. By recognizing the clinical seizure pattern, with or without EEG confirmation, seizure onset may be attributed to one particular lobe (e.g., temporal lobe) or localized brain region (e.g., supplementary motor area). Further, they may be described according to whether consciousness (awareness) is retained (see Table 10–1). The terms “complex” and “simple” may be confusing; therefore, it has been recommended that these terms should no longer be used. The term “dyscognitive” has been proposed for impaired awareness (if this can be determined).¹

EVALUATION: GENERAL PRINCIPLES

The evaluation should begin with a detailed description of the attack by an eyewitness (See Fig. 10–1). Any indication of a warning, focal motor components, or stereotyped changes in behavior suggest focal onset. An EEG is likely to show interictal epileptic abnormalities (sharp waves, spikes, spike, and slow wave) in the awake state in approximately 50% (see Fig. 10–2); this may rise to 85% if a sleep recording is obtained. The EEG is often localizing in children presenting with focal epilepsy, particularly in the older child. Where seizure manifestations and the EEG suggest a particular epilepsy syndrome, particularly in a developmentally normal child, further investigation may not be required. However, most children presenting with focal epilepsy require detailed MR imaging to exclude a structural brain abnormality.³

Further evaluation may be necessary to determine if the seizure and EEG pattern are consistent with a specific epilepsy syndrome. This information will result in optimal medication, more accurate prognosis for seizure control and neurodevelopmental outcome. If imaging is negative, with seizure control by medication no further investigation may be required. If a unilateral lesion on imaging is identified, referral for evaluation for epilepsy surgery should be considered early in the natural history (see Chapter). Ictal video-EEG telemetry will be required to determine the area of seizure onset; further investigation that may help in determining whether surgery may be an option includes fluorodeoxyglucose (FDG) positron emission tomography (that may reveal an area of hypometabolism consistent with a structural area responsible for seizures), magnetoencephalography (which may point to a focal area with dipole localization), or other functional studies (e.g., ictal and interictal single-photon emission computed tomography, functional MRI). Such investigations are only useful in presurgical evaluation, in the hands of those experienced in surgical assessment.

In rare circumstances, the pattern of seizures and EEG may suggest genetic causes; this may be seen where focal seizures may be the presenting feature in the first year of life as prolonged lateralized convulsions (SCN1A mutation) or frontal lobe seizures in early life in the context of normal imaging with episodes of nonconvulsive status epilepticus (ring chromosome 20). However, research now reveals an increasing number of the epilepsies likely to have a genetic etiology.

FOCAL SEIZURES IN THE NEONATE

Most epileptic seizures in the neonatal period are focal⁴ and may present as focal clonic or focal tonic movement.⁵ Further, paroxysmal changes in autonomic function have also been reported including changes in heart rate, respiration, and blood pressure associated with flushing, salivation, and pupillary dilatation.^6,7 These features are rare as isolated manifestations of epileptic events and are more consistently observed in association with other clinical evidence of epileptic seizures. EEG recordings of neonatal seizures have wide-ranging features; the frequency, voltage, and morphology of the discharges may change within an individual seizure; EEG transients commonly arise focally and may either remain confined to that region or spread (see Chapter 9).

FOCAL SEIZURES IN INFANCY

In the very small child, where networks have not fully matured, components of focal seizures may be subtle and simple in their manifestation. Generalized seizures are rarely documented in video-EEG studies in infants under age 2 years.^8,9 Secondarily generalized clinical manifestations may arise from focal lesions, and seizures may evolve into infantile spasms even with evidence of focality in the original presentation (see Fig. 10–3),^10,11 whereas others may retain focal symptomatology.