Answer
West syndrome is a triad of infantile spasms, developmental retardation or regression, and hypsarrhythmia on electroencephalogram (EEG). The syndrome presents in infants aged between 6 and 18 months.
The presence of a hypsarrhythmic EEG confirms the diagnosis of infantile spasms (see the following image). EEG patterns may evolve over a time period; they initially appear in the sleep EEG record and subsequently present during the awake state. Hypsarrhythmia is seen in 75% of patients with West syndrome.
Electroencephalogram demonstrating hypsarrhythmia in infantile spasms. Note the chaotic high-amplitude background.
Hypsarrhythmia consists of diffuse giant waves (high voltage, >400 microvolts [µV]) with a chaotic background of irregular, multifocal spikes and sharp waves and very little synchrony between the cerebral hemispheres. During sleep, the EEG may display bursts of synchronous polyspikes and waves. A pseudoperiodic pattern may be evident. Persistent slowing or epileptiform discharges in the hypsarrhythmic background may be present and may represent an area of focal dysfunction. Several variations to the hypsarrhythmic pattern, which are referred to as hypsarrhythmic variants, may be noted.
Clinical spasms are associated with a marked suppression of the background that lasts for the duration of the spasm. This characteristic response is called the electrodecremental response (see the image below).
Electroencephalogram demonstrating hypsarrhythmia. Note the electrodecremental response that is associated with a spasm in infantile spasms (ie, West syndrome).
EEG is useful in judging successful treatment of West syndrome. Typically, shortly after treatment with adrenocorticotropic hormone (ACTH) or vigabatrin is initiated, the spasms stop and hypsarrhythmia disappears.
Hypsarrhythmia rarely persists beyond the age of 24 months. It may evolve into the slow spike and wave discharges seen in Lennox-Gastaut syndrome.
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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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Typical 3-Hz electroencephalographic spike and wave discharges seen in absence epilepsy.
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Electroencephalogram demonstrating absence epilepsy. Anteriorly dominant, typical 3-Hz spike and wave discharges.
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Benign rolandic epilepsy associated with typical centrotemporal electroencephalographic spikes.
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Electroencephalogram demonstrating benign rolandic epilepsy. Note the characteristic spike and waves seen in drowsiness.
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Electroencephalogram demonstrating polyspike and wave discharges seen in juvenile myoclonic epilepsy.
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Electroencephalogram demonstrating polyspike and wave response produced by photic stimulation.
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Electroencephalogram demonstrating polyspike and wave discharges, which can be seen in idiopathic generalized epilepsy.
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Electroencephalogram demonstrating paroxysmal fast activity as can be seen in Lennox-Gastaut syndrome.
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Electroencephalogram demonstrating interictal pattern (sharp waves) in left temporal lobe epilepsy.
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Electroencephalogram demonstrating interictal pattern of independent left and right temporal sharp waves, which can be seen in temporal lobe epilepsy.
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Electroencephalogram demonstrating a left temporal lobe seizure (beginning) with 2-3 Hz rhythmic delta activity.
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Electroencephalogram demonstrating a left temporal lobe seizure (middle), evolving to rhythmic theta activity.
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Electroencephalogram demonstrating a left temporal lobe seizure (end), further evolving to diffuse delta activity prior to abrupt cessation.
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Electroencephalogram of a right occipital lobe seizure (beginning); 4-5 Hz repetitive sharp waves (maximal T6/O2).
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Electroencephalogram demonstrating spike-wave complexes as can be seen in idiopathic generalized epilepsy.
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Electroencephalogram demonstrating right temporal lobe seizure (beginning); rhythmic delta activity evolving to rhythmic theta activity over the right temporal region.
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Electroencephalogram demonstrating a right temporal lobe seizure (middle); continued right temporal rhythmic theta activity.
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Electroencephalogram demonstrating a right temporal lobe seizure (end), resolution of right temporal rhythmic theta.
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Electroencephalogram demonstrating interictal pattern of extratemporal spikes (left hemispheric spike and wave).
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Electroencephalogram demonstrating interictal pattern of extratemporal spikes (right posterior spikes, temporoparietal).
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Electroencephalogram demonstrating interictal pattern of extratemporal spikes (left posterior spikes, temporoparietal).
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Electroencephalogram demonstrating repetitive central spikes (maximal Cz).
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Electroencephalogram demonstrating repetitive central sharp waves (maximal Cz).
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Electroencephalogram demonstrating repetitive left frontocentral sharp waves (maximal Cz).
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Electroencephalogram demonstrating a left fronto-central seizure (beginning); rhythmic 14-16 Hz activity (maximal Cz and C3).
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Electroencephalogram demonstrating a left fronto-central seizure (end); evolution to rhythmic 11-12 Hz activity with slightly higher amplitude with abrupt cessation.
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Electroencephalogram demonstrating a right frontal lobe seizure (beginning); rhythmic 2-3 Hz activity (maximal Fp2).
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Electroencephalogram demonstrating a right frontal lobe seizure (maximal Fp2) (end).
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Electroencephalogram demonstrating a right frontal lobe seizure (beginning); repetitive ~3 Hz sharp waves (maximal F4/F8).
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Electroencephalogram demonstrating a right frontal lobe seizure (middle); repetitive ~3 Hz sharp waves (maximal F4/F8).
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Electroencephalogram demonstrating a right frontal lobe seizure (end); rhythmic sharply contoured ~2 Hz bi-frontal delta activity.
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Electroencephalogram of a right occipital lobe seizure (middle); repetitive sharp waves evolve to rhythmic theta in the right occipital region.
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Electroencephalogram of a right occipital lobe seizure (end); obscured by EMG artifact.
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Electroencephalogram demonstrating a run of generalized polyspikes, which are more left predominant and can be seen in idiopathic generalized epilepsies.
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Typical absence seizure with 3-4 Hz rhythmic generalized spike and wave discharges with abrupt onset and end.
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Electroencephalogram demonstrates bilateral repetitive occipital sharp waves ~1Hz frequency.
