Laboratory Studies
The following studies are intended to determine the etiology:
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Electrolyte evaluation
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CBC count
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Metabolic testing
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Genetic testing
Imaging Studies for SGE
MRI of the brain is also used to determine the etiology.
Other Tests for SGE
EEG
The EEG in symptomatic generalized epilepsy (SGE) typically reveals epileptiform abnormalities and other evidence of diffuse brain dysfunction (various degrees of slowing). As the brain develops from neonate to adolescent, the epileptiform abnormalities can also change.
In neonates with SGE, early myoclonic encephalopathy and Ohtahara syndrome have EEG findings with a suppression-burst pattern. The myoclonic jerks of early myoclonic encephalopathy correlate with the burst of spikes, sharp waves, and slow waves lasting 1-5 seconds on EEG, with periods of suppression of 3-10 seconds with no normal background. [7, 15]
The EEG in Ohtahara syndrome shows bursts of 2-6 seconds of wide amplitude spikes and polyspikes that alternate with 3-8 seconds of suppressed electrical activity. Later in infancy, the burst-suppression pattern is replaced by continuous multifocal spikes and slow waves of large amplitude or hypsarrhythmia, as is seen in infantile spasm. [1] The hypsarrhythmia represents spread of epileptic activity when the brain has not developed inhibition. [9]
As the brain continues to mature, EEG patterns in children with SGE can evolve into a generalized, high-amplitude, synchronous, slow spike, polyspike, and slow wave discharges of 1.5-2.5 Hz, as is seen in Lennox-Gastaut syndrome. [6] The interictal EEG shows a generalized slow spike-wave pattern, further activated by drowsiness and sleep. [16]
EEG findings progressive myoclonic epilepsy reveal a specific pattern unique to the syndrome. EEG in Lafora disease reveals occipital spikes in 50% of patients.
Unverricht-Lundborg disease EEG findings reveal background slowing in theta frequency, with a 3-5 Hz polyspike, and waves discharge with sporadic focal spikes and wave discharges.
EEG in patients with sialidosis reveals progressive slowing of background activity with bilateral spike and wave activity, which is photosensitive.
Beyond early childhood and almost regardless of etiology, the typical EEG of SGE includes slow (< 2.5 Hz) spike and wave complexes and multifocal spikes. Ictal patterns are described in EEG-video monitoring.
For more information, see EEG in Common Epilepsy Syndromes and Generalized Epilepsies on EEG.
Procedures for SGE
No procedures are indicated, except for in specific neurodegenerative diseases that are typically investigated during childhood. If the latter conditions are suspected, then cerebrospinal fluid analysis should be performed. If a specific genetic condition is suspected, then chromosomal analysis or skin biopsy for electron microscopy may be diagnostic.
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Atonic seizure. Abrupt loss of muscle tone is followed by clonic rhythmic movements. This type of seizure is typical for the symptomatic generalized epilepsies of the Lennox-Gastaut type.
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Electroencephalogram demonstrating hypsarrhythmia in infantile spasms. Note the chaotic high-amplitude background.
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Electroencephalogram demonstrating hypsarrhythmia. Note the electrodecremental response that is associated with a spasm in infantile spasms (ie, West syndrome).
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Slow (< 2.5 Hz) electroencephalographic spike and wave discharges associated with atypical absence seizures (ie, Lennox-Gastaut syndrome).
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Slow (< 2.5 Hz) electroencephalographic spike and wave discharges in atypical absence epilepsy (ie, Lennox-Gastaut syndrome).
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Spike, generalized. Significant spikes usually are followed by a slow wave, as shown here. This example also illustrates that generalized spikes are typically maximal frontally. This is typical of primary (ie, idiopathic, genetic) epilepsies. If burst lasted 3 seconds or more, it could be classified as spike-wave complexes.
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Slow spike-wave complexes. In addition to being slower, they are also less monomorphic than 3-Hz spike-wave complexes. With other findings, this often is seen in symptomatic/cryptogenic epilepsies of Lennox-Gastaut type.
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Slow spike-wave complexes. In addition to being slower, they are also less monomorphic than 3-Hz spike-wave complexes. With other findings, this often is seen in symptomatic/cryptogenic epilepsies of Lennox-Gastaut type.
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Hypsarrhythmia. High-amplitude slowing with no organized background and multifocal spikes (left and right frontal in this sample). This is phenotype of first year of life and is associated with West syndrome (ie, infantile spasms).
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Hypsarrhythmia. High-amplitude slowing (note scale) with no organized background and multifocal spikes (right frontal and left occipital in this sample). This is phenotype of first year of life and is associated with West syndrome (ie, infantile spasms).
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Generalized paroxysmal fast activity and electrodecrement. This pattern is characteristic of symptomatic/cryptogenic epilepsies of Lennox-Gastaut type and may be subclinical or associated with tonic or atonic seizures.
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Typical generalized tonic seizure in an adult patient with a "symptomatic" (now termed structural-metabolic) generalized epilepsy of the Lennox-Gastaut type.
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Typical generalized tonic seizure in a patient with a "symptomatic" (now termed structural-metabolic) generalized epilepsy of the Lennox-Gastaut type and severe static encephalopathy with cerebral palsy.
