-onset seizures, which differ according to the type of seizure. Focal-onset and generalized-onset seizures also differ in that generalized-onset seizures have greater similarity between their ictal and interictal EEG patterns (<A onclick="
▲ Ictal Patterns for Focal-onset Seizures
Types and Other Names
Ictal patterns for focal seizures
Ictal patterns for partial seizures
Ictal rhythms
Electrographic seizures
Subclinical seizures
Description
By definition, the ictal pattern for a focal-onset seizure is simply the EEG finding that is present during the seizure. This definition is more reliable than any morphologic description because the EEG manifestations of focal-onset seizures are diverse (Westmoreland, 1998). However, two characteristics are expected. The ictal pattern is almost always stereotyped across seizures for the individual patient, and the pattern typically includes evolving rhythms or repetitive sharp waves. Evolution of the ictal activity is a key feature and it benefits the ictal pattern’s identification even when the pattern occurs amid activity that has similar frequencies or sharp wave features. When the ictal pattern arises from faster or less regular rhythmic activity, the progressive change in waveform is the identifying feature for the seizure onset (Blume et al., 2002). Infrequently, the ictal pattern does not include evolution and instead manifests as desynchronization, regular repetitive spikes, or regular rhythmic slowing (Fisch, 1999; Niedermeyer, 1999b). These nonevolving and desynchronization patterns most commonly accompany focal motor seizures without cognitive impairment. Regardless of the type of ictal pattern, focal-onset seizures do not differ in their EEG pattern according to the location of the focus or whether the seizure remains focal or evolves into a generalized seizure. This contrasts with the ictal patterns for generalizedal but may be generalized, because secondary bilateral synchrony does not demonstrate ictal evolution. Its first appearance includes its broad distribution.
The electrographic resolution of focal-onset seizures is a continued evolution that usually is either evolution into the background activity that was present before the seizure or evolution into repetitive epileptiform bursts (Fisch, 1999). These bursts are then followed by either slowing or suppression with the maximal slowing, or suppression often occurring in the ictal-onset zone. Increased focal IED occurrences may also occur postictally in the ictal-onset zone, and the resolution of the IEDs occurs more gradually than the seizure resolution (Blume et al., 2002).
Distinguishing Features
• Compared to Focal Rhythmic Activity (Alpha, Beta, Theta, or Delta)
Since the ictal pattern of a focal-onset seizure typically includes repetitive focal activity, the pattern must be distinguished from a burst of normal activity within one frequency band. Among the focal rhythms, rhythmic midtemporal theta activity and the wicket rhythm are the two patterns that are most likely to need differentiation from the ictal rhythm of a focal-onset seizure because both of these rhythms have a temporal region location, which is a common seizure localization, and temporal lobe seizures usually have ictal patterns within the theta, and sometimes alpha, frequency ranges.
Evolution is the feature that most often and most straightforwardly distinguishes ictal patterns from normal rhythmic activity. Although nonevolving rhythmic delta activity may be the ictal pattern for some focal-onset seizures, most focal-onset seizures with rhythmic activity demonstrate clear evolution. Stereotypy across occurrences is a possibly distinguishing feature because it is an expected characteristic of seizures, and this also applies to delta activity without evolution. However, normal bursts of rhythmic activity may be relatively stereotyped. Association with changes in the surrounding regions is another distinguishing feature. Ictal patterns often follow or precede either runs of co-localized focal IEDs or periods of attenuation, and they also may be followed by broad and abnormal slowing. Of course, the most important distinguishing feature is whether the pattern is associated with a similarly stereotyped behavioral change, which is the actual seizure. This feature is the most important because any electrographic pattern could be considered an ictal pattern if it reliably corresponds to a patient’s behavioral seizure.
• Compared to Fourteen and Six Per Second Positive Spikes
Ictal patterns for focal-onset seizures and fourteen and six positive bursts (14&6) may be similar by both demonstrating evolving focal activity. However, the two patterns are distinguishable in their duration and distribution. The 14&6 usually lasts less than 1 second and rarely lasts more than 2 seconds. Ictal patterns for focal-onset seizures usually last at least several seconds. More distinguishing is the occurrence of 14&6 bilaterally, either synchronously or, more importantly, asynchronously. Focal-onset seizures rarely have bilateral fields at their onset. Secondary bilateral synchrony is the exception to this, but neither secondary bilateral synchrony nor any other type of focal-onset seizure has a bilateral and independent activity. Even if a 14&6 pattern during one occurrence appears suggestive of an ictal pattern, other occurrences during the same EEG are likely to be present and these often manifest in other 14&6 forms.
• Compared to Subclinical Rhythmic Electrographic Discharge ossion with the maximal slowing, or suppression often occurring in the ictal-onset zone. Increased focal IED occurrences may also occur postictally in the ictal-onset zone, and the resolution of the IEDs occurs more gradually than the seizure resolution (Blume et al., 2002).
Distinguishing Features
• Compared to Focal Rhythmic Activity (Alpha, Beta, Theta, or Delta)
Since the ictal pattern of a focal-onset seizure typically includes repetitive focal activity, the pattern must be distinguished from a burst of normal activity within one frequency band. Among the focal rhythms, rhythmic midtemporal theta activity and the wicket rhythm are the two patterns that are most likely to need differentiation from the ictal rhythm of a focal-onset seizure because both of these rhythms have a temporal region location, which is a common seizure localization, and temporal lobe seizures usually have ictal patterns within the theta, and sometimes alpha, frequency ranges.
Evolution is the feature that most often and most straightforwardly distinguishes ictal patterns from normal rhythmic activity. Although nonevolving rhythmic delta activity may be the ictal pattern for some focal-onset seizures, most focal-onset seizures with rhythmic activity demonstrate clear evolution. Stereotypy across occurrences is a possibly distinguishing feature because it is an expected characteristic of seizures, and this also applies to delta activity without evolution. However, normal bursts of rhythmic activity may be relatively stereotyped. Association with changes in the surrounding regions is another distinguishing feature. Ictal patterns often follow or precede either runs of co-localized focal IEDs or periods of attenuation, and they also may be followed by broad and abnormal slowing. Of course, the most important distinguishing feature is whether the pattern is associated with a similarly stereotyped behavioral change, which is the actual seizure. This feature is the most important because any electrographic pattern could be considered an ictal pattern if it reliably corresponds to a patient’s behavioral seizure.
• Compared to Fourteen and Six Per Second Positive Spikes
Ictal patterns for focal-onset seizures and fourteen and six positive bursts (14&6) may be similar by both demonstrating evolving focal activity. However, the two patterns are distinguishable in their duration and distribution. The 14&6 usually lasts less than 1 second and rarely lastf Adults
Unlike typical ictal patterns for focal-onset seizures, subclinical rhythmic electrographic discharge of adults (SREDA) does not have evolution in its distribution across the scalp or in its waveform, and it does not lead to slowing following its resolution. Furthermore, the alpha rhythm is often unaffected by SREDA, which rarely occurs after the focal seizure’s ictal pattern spreads contralaterally or across the posterior head region. Most importantly, SREDA is not associated with any alteration in awareness or any other behavioral change.
Co-occurring Patterns
Focal-onset seizures do not have the bilateral and forceful movements of generalized-onset convulsive seizures, but they still commonly produce significant movement or a muscle artifact. During focal-onset seizures with automatisms, this may be an electromyographic artifact from repetitive facial movements, ocular artifact from repetitive blinking, or glossokinetic artifact from repetitive swallowing. The mild attenuation preceding and the slowing following the seizure are other associated patterns. An increase in IEDs after the seizure also occasionally occurs.
Clinical Significance
Similar focal-onset ictal patterns may produce seizures with disparate ictal experiences and behaviors across different individuals (Amit and Crumrine, 1993). That is, the focal-onset ictal pattern does not indicate the type of seizure manifestation
with meaningful reliability. However, the ictal pattern usually is accompanied by a stereotyped behavioral change within the unimaginably diverse behavioral manifestations of focal seizure focal-onset ictal patterns may produce seizures with disparate ictal experiences and behaviors across different individuals (Amit and Crumrine, 1993). That is, the focal-onset ictal pattern does not indicate the type of seizure manifestation
with meaningful reliability. However, the ictal pattern usually is accompanied by a stereotyped behavioral change within the unimaginably diverse behavioral manifestations of focal seizures. Sometimes, no behavioral change is either evident or recognized to occur during an ictal pattern highly suggestive of a focal-onset seizure, but the lack of recognized behavioral change does not mean that a seizure has not occurred. Focal seizures commonly produce behavioral changes that may be overlooked by others because there are no unusual movements and the seizure’s clinical manifestation is limited to impairment of memory and concentration. As such, the patient also may not be aware of the seizure’s occurrence. Detailed cognitive testing during and after a seizure may be the only way of determining if a dyscognitive focal seizure has occurred.
with meaningful reliability. However, the ictal pattern usually is accompanied by a stereotyped behavioral change within the unimaginably diverse behavioral manifestations of focal seizure focal-onset ictal patterns may produce seizures with disparate ictal experiences and behaviors across different individuals (Amit and Crumrine, 1993). That is, the focal-onset ictal pattern does not indicate the type of seizure manifestation
with meaningful reliability. However, the ictal pattern usually is accompanied by a stereotyped behavioral change within the unimaginably diverse behavioral manifestations of focal seizures. Sometimes, no behavioral change is either evident or recognized to occur during an ictal pattern highly suggestive of a focal-onset seizure, but the lack of recognized behavioral change does not mean that a seizure has not occurred. Focal seizures commonly produce behavioral changes that may be overlooked by others because there are no unusual movements and the seizure’s clinical manifestation is limited to impairment of memory and concentration. As such, the patient also may not be aware of the seizure’s occurrence. Detailed cognitive testing during and after a seizure may be the only way of determining if a dyscognitive focal seizure has occurred.
A focal seizure may also occur without behavioral change or cognitive impairment and manifest purely as a subjective experience. These experiences are stereotyped, just as other focal seizures, and may be a sensory illusion or hallucination, an emoti.title; return true;” onmouseout=”window.status=”; return true;”>Berg et al., 2010). A description of the patient’s behavior and mentation is a more reliable means to characterize focal seizures, and this approach has been used here.
The ictal pattern often does not necessarily indicate the epileptogenic region or even its lateralization, as can be identified with a comprehensive epilepsy surgery evaluation (Sharbrough, 1993). The epileptogenic region is defined as the region necessary and sufficient to produce the patient’s habitual seizures, and the ictal pattern’s focus instead provides one determination of what is termed the ictal-onset zone. Other techniques, such as ictal magnetoencephalography, ictal SPECT, and ictal intracranial EEG, may demonstrate different ictal-onset zones for the same seizure, and this demonstrates the dependence of ictal-onset zone localization on the technology that is employed. However, the ictal-onset zone, regardless of the technology used to identify it, provides a valuable component in the localization of the putative epileptogenic region, even if it is an approximation.
Estimating the accuracy of the ictal pattern’s focus depends on its concordance with the other diagnostic tests and particular features within the ictal pattern. Lateralized rhythmic theta or 23e333153e8e664970a21b04ea3dd0dfc84ada3f783c4a27}/ID(RU2-13)” title=”Bare et al., 1994″ onmouseover=”window.status=this.title; return true;” onmouseout=”window.status=”; return true;”>Bare et al., 1994). In contrast, patterns that are identical to the ictal patterns of focal-onset seizures also can occur without any true behavioral or functional change. These have been termed “subclinical” or “electrographic” seizures, and they are discussed in the next subsection, Ictal Patterns of Generalized-onset Seizures.
Focal-onset seizures without generalization was divided by the International League Against Epilepsy (ILAE) into simple partial and complex partial seizures with simple partial indicating a focal seizure without impairment of consciousness and complex partial indicating an impairment in consciousness (Commission on Classification and Terminology of the International League Against Epilepsy, 1981). Since consciousness is a complicated phenomenon, complex partial has commonly been operationally defined as demonstrating impairment of memory or concentration during the seizure. This distinction is clinically important because of the greater risk for injury when consciousness is impaired, but assessing consciousness during a seizure can be difficult and inaccurate. As such, the division of partial seizures into simple and complex has been reconsidered by the ILAE with elimination of the terms simple and complex as descriptions of seizures and recommendation of the term dyscognitive as a more accurate and informative description (<A onclick="if (window.scroll_to_id) { scroll_to_id(event,'RU3-13'); return false; }" onmouseover="window.status=thisfor 82% of patients whose ictal pattern is a phase-reversing rhythm over the anterior temporal lobe that reaches a frequency of 5 Hz or greater within 30 seconds (Risinger et al., 1989Sharbrough, 1993
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