In clinical practice, epileptic seizures with focal onset and subsequent generalized motor involvement are referred to as secondarily generalized seizures.1,2 However, generalized motor manifestations do not necessarily imply that the entire or even bilateral cerebral cortex is producing the epileptic discharges.3 Focal seizures arising from the supplementary motor cortex or basal ganglia also can produce clinical signs of generalized motor activity.4 Conversely, bilateral and widely spread ictal electroencephalographic (EEG) patterns can be found in patients with minimal or subtle motor activity during a secondarily generalized seizure (Case 11-1).5 Thus, the operational definition of secondary generalization in the era of video-EEG monitoring (VEM) should be focal onset of an epileptic seizure with generalized or bilateral ictal electrographic propagation.6 According to the classification by the International League Against Epilepsy (ILAE), there are three different types of secondarily generalized seizures: tonic-clonic seizures, absence seizures, and epileptic spasms (Table 11-1).1,7,8 Differences in clinical presentation and EEG findings of these seizure types are compared in Table 11-2. Although partial onset seizures do not commonly progress to secondarily generalized seizures, more than 60% of patients with partial seizures may experience tonic-clonic seizures.9 Not all secondarily generalized convulsions progress from complex partial seizures, and up to 20 to25% of them are directly evolved from simple partial seizures, which suggests multiple cortical and subcortical routes of spread are possible for secondary generalization.10
Case 11-1
At age 49, as the patient’s family noted, the patient tended to “fall into [sic] sleep easily,” with extreme difficulty of arousal. Her brain magnetic resonance imaging (MRI) and EEG were normal, and the diagnosis of epilepsy was eventually made about 8 years later. The beginning of Video 11-1 corresponds to the arrow in Figure 11-1, which already shows diffuse ictal rhythmic theta changes bilaterally. Even though the patient’s ictal EEG showed a secondarily generalized pattern, she had little or subtle motion, without the appearance of tonic or clonic activity.
Figure 11-1.
Electroencephalographic (EEG) onset of Case 11-1. Ictal EEG changes 20 seconds after the initial EEG onset in Case 11-1. Ictal EEG changes 35 seconds after the EEG onset and start of the clinical seizure in Case 11-1. EEG shows bilateral diffuse rhythmic 4 to 5 Hz discharges. Ictal EEG changes 55 seconds after the EEG onset in Case 11-1, showing diffuse bilateral changes.
| Type of Seizure | Description |
|---|---|
| Tonic-clonic seizures | Probably consist of multiple types and may involve different pathophysiologic mechanisms and anatomical substrates, at least initially, than generalized tonic-clonic seizures with generalized onset |
| Absence seizures | Rarely represent propagation from localized cortical areas, usually in the frontal lobe; there may be a continuum between these events and generalized atypical absences |
| Epileptic spasms | Can occur in infants with focal lesions; the mechanism by which these generalized events are generated is unknown |
| Tonic-Clonic | Absence | Epileptic Spasms | |
|---|---|---|---|
| Semiology | Evolving stiffening of body and limb muscles (tonic), followed by semirhythmic jerking motion of extremities (clonic) | Sudden cessation of behavior, motion, and speech; may have lip smacking and other automatisms | Sudden flexion or extension of axial and proximal limb muscles |
| Duration of seizures | Usually 20 to 90 s | Typically 1 to 10 s | 0.5 to 2.5 s, but may cluster |
| Background EEG | Normal symmetrical background, but asymmetric background can be seen if associated with focal lesions | No significant background asymmetry between two hemispheres | Frequently abnormal with diffuse high-voltage slowing; asymmetric background or lack of synchrony is not uncommon |
| Ictal EEG | Evolving SWDs over both hemispheres at 6 to 8 Hz (asymmetric may be seen), often mixed with MMAs | Generalized 2.5 to 4.0 Hz SWDs with frontal dominance bilaterally | Initial high-voltage diffuse slow wave, followed by voltage attenuation and/or a low-voltage fast beta rhythm; although clinical spasms last a few seconds, ictal voltage attenuation may last up to 10 s |
| Paroxysmal discharges | Focal SWDs or intermittent slow waves | Frequently shows fragmented SWDs and/or generalized 2.5 to 3.5 Hz SWDs | Frequent multifocal and generalized SWDs or high-amplitude delta waves |
| EEG during activations | Focal discharges more frequent during NREM sleep, but usually not with HV or PS | Generalized SWDs more frequent with HV, PS, and drowsiness/sleep | Usually no significant effects with HV or PS; multifocal or generalized SWD may increase with sleep |
As mentioned earlier in the book, epilepsy is one of the most common neurologic disorders, affecting up to 2% of the population worldwide, and almost 2 million people in the United States alone. Estimated annual incidences of partial seizures are higher in the older population. For people younger than 60 years, the incidence of partial seizures is 20 cases per 100,000 person years. For people ages 60 to 80 years, the incidence increases to 80 cases per 100,000 person years. Although the exact prevalence of secondary generalized seizure is not known, it is estimated that 20% of epilepsy patients may experience secondary generalized seizures in their lifetime. 11–13
Epileptic seizures with combinations of tonic and clonic motor activity involving bilateral body parts, including the arms, legs, trunk, and head, are called generalized tonic-clonic seizures. Tonic-clonic seizures are what most patients would refer to as grand mal seizures, although grand mal does not distinguish between primary generalized and secondarily generalized motor seizures. However, partial onset seizures are the more common form of generalized motor seizure. Although the term grand mal is commonly used to describe apparent convulsive or “big” seizures, the origin of the terminology came from medieval French to describe a divine or great disease (morbus divinus or morbus maior), as epilepsy was once believed to be a sacred disease.14 In primary generalized tonic-clonic seizures, tonic posturing occurs simultaneously at the onset of the seizure, with ictal EEG showing epileptiform discharges over both cerebral hemispheres. In seizures with focal onset, different muscle groups may be involved sequentially as the seizure discharges propagate, with EEG showing focal discharges and subsequent spreading of epileptiform activity. This seizure presentation is commonly referred to as secondarily generalized tonic-clonic seizures (SGTCS).
SGTCS are the most common type of secondarily generalized seizures. Specific movements of the arms and legs and/or the face may occur with loss of consciousness. A yell or cry often precedes the loss of consciousness. The person may abruptly fall and begin to have jerking movements of his or her body and head. Drooling, biting of the tongue, and incontinence of urine may occur. The tonic-clonic activity typically lasts <2 minutes,15,16 followed by postictal confusion. Theodore et al. found that the mean duration of SGTCS was only 62 seconds.10 Some patients may experience prolonged weakness after their seizures (Todd’s paralysis).17 SGTCS consist of clinically and electrographically different seizures and may involve different pathophysiologic mechanisms and anatomical substrates. Although partial onset seizures arising from any anatomical location can evolve into SGTCS, seizures with temporal lobe origin are most frequently associated with SGTCS (Case 11-2). Previous studies suggest that the left temporal lobe origin could have a higher incidence of secondary generalization, impacting potential medical and surgical treatment of complex partial seizures depending on the side that the seizure originated from.18 Extratemporal seizures originate from the frontal, central, parietal, occipital, and midline regions of the brain (Case 11-3). The scalp EEG can show various types of interictal and ictal discharges consisting of spikes, spikes and waves, sharp waves, paroxysmal fast activity, or rhythmic activity in the beta, alpha, theta, or delta frequency ranges.19,20 The discharges can occur as focal, regional, lateralized, or secondarily generalized discharges. Oftentimes, it is difficult to discern the origin of seizures based on ictal progression of EEG patterns alone because some extratemporal seizures can be mistakenly thought to originate from the temporal lobe, as the temporal lobe tends to become involved early during secondary generalization.21–23
Case 11-2
The patient is a 46-year-old woman with seizures since age 21. Her typical seizure starts with an “uprising cold sensation,” followed by unresponsiveness and convulsion lasting about 30 to 45 seconds. Her brain MRI revealed atrophy of the right hippocampus. Video 11-2 shows a partial seizure progressed to SGTCS with ictal cry, left hand posturing, and head deviation to the left. Ictal EEG showed initial rhythmic theta discharges from the right temporal region with gradual progression to spike and wave discharges (SWDs) (Figure 11-2). Maximal phase reversing was seen at the anterior temporal FT10 electrode (arrow in Figure 11-2C). Subsequently, the patient underwent selective amygdalohippocampectomy and became seizure-free.
Figure 11-2.
Initial ictal EEG changes in Case 11-2 showing rhythmic pattern at the right temporal region. Ictal EEG changes 10 seconds after the seizure onset in Case 11-2. Previously seen rhythmic discharges are now seen bilaterally but still better seen over the right temporal region. Ictal EEG changes 20 seconds after the seizure onset in Case 11-2. Better ictal progression is seen over the right temporal region. Arrow points to the maximal phase reversing at the anterior temporal FT10 electrode.
Case 11-3
The patient is a 21-year-old ambidextrous man who had seizures since age 2 months. His seizures were described as “jumping out of bed and kicking” at night, and about two thirds of the time, his seizure progressed to tonic–clonic activity. Although his seizures typically lasted <30 seconds, he had noticeable aphasia after them. His brain MRI was normal, and outpatient EEG showed diffuse left-sided epileptiform discharges. During VEM, he had four seizures in one night, all of which occurred during sleep (Video 11-3). His seizure semiology is typical for a frontal lobe seizure with explosive hypermotor activity. His EEG showed muscle and motion artifacts initially (Figure 11-3), followed by diffuse low-voltage fast discharges during his tonic phase toward the end.
Figure 11-3.
Ictal EEG changes associated with Case 11-3. EEG shows muscle and motion artifacts only at the beginning of the clinical onset.
Case 11-4
This patient has medically refractory partial epilepsy, but previous VEM with scalp electrodes did not reveal a clear seizure focus clinically or electroencephalographically (Video 11-4). Subsequently, he underwent invasive monitoring with intracranial depth wire electrodes, which showed low-voltage fast beta frequency discharges arising from the LA1-2 and LH1-2 electrodes at the onset (Figure 11-4), along with voltage attenuation at LA3-6 and LH3-6 electrodes. He had five additional seizures with a similar pattern and received selective amygdalohippocampectomy with complete resolution of his seizures.
Figure 11-4.
Intracranial ictal EEG showing low-voltage fast frequency discharges arising from the LA1-2 and LH1-2 electrodes at the onset of seizure in Case 11-4. LA/RA, left/right amygdala electrodes (LA1 and RA1 approximate amygdala nuclei); LO/RO, left/right orbitofrontal electrodes. Further ictal progression over the LA1-2 and LH1-2 electrodes, as well as diffuse slowing (left > right) in 10 seconds (Case 11-4). Further ictal EEG changes 30 seconds after the EEG onset in Case 11-4.
Case 11-5
The patient had a resection of a right parafalcine meningioma at age 23, and about 1 year later, he had his first seizure. His seizures now frequently involve convulsions and are quite refractory to multiple medications. His background EEG (EEG 5-background) revealed an expected breach rhythm (arrow A in Figure 11-5) from his prior surgery over the right central region, as well as intermittent 3.0 to 3.5 Hz rhythmic slow waves (arrow B). His clinical seizure showed initial head and eye deviation to the left, followed by a tonic-clonic convulsion approximately 15 seconds later (Video 11-5). His ictal EEG, however, revealed bilateral SWDs at the onset (Figure 11-5A), followed by prominent low-voltage fast discharges located diffusely over the right hemisphere (Figure 11-5B). Subsequent EEG changes were seen associated with clinical tonic (Figure 11-5C) and clonic phases (Figure 11-5D, E). Considering the patient’s surgical history, ictal semiology, and ictal progression, his seizure is most likely a partial onset seizure, although the ictal EEG onset resembles that of a generalized onset seizure.
Figure 11-5.
Interictal background EEG in Case 11-5, showing breach rhythm (arrow A) over the right central region and intermittent 3.0 to 3.5 Hz rhythmic slow waves (arrow B). Sudden clinical and EEG seizure onset in Case 11-5, showing bilateral spike and slow wave discharges. Five seconds after the seizure onset in Case 11-5, showing more prominent low-voltage fast discharges over the right hemisphere. Ictal EEG changes during tonic phase in Case 11-5, showing faster sharp discharges diffusely over both hemispheres. Ictal EEG changes during the end of the clonic phase in Case 11-5.
Typical absence seizures are defined as brief generalized epileptic seizures of sudden onset and termination with impairment of consciousness, with ictal EEG findings of generalized 3 to 4 Hz SWDs.24 According to both the 1981 and 1989 Commission on Classification and Terminology of the ILAE, typical absence seizures are categorized as generalized onset seizures.25–27 Like other idiopathic generalized epilepsies, children with absence seizures tend to have a strong genetic predisposition and are otherwise normal.24,28,29
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