Generalized sharp activity is usually associated with a slow wave, forming the spike- wave complex. Spike-wave complexes correlate better than single spike discharges with clinical seizures. Generalized spike-wave discharges fall into four categories:
• 3-per-second spike-wave complex • slow spike-wave complex
• fast spike-wave complex
• 6-per-second spike-wave complex
3-per-second spike-wave
The 3-per-second spike-wave complex is usually equated with absence epilepsy. Although there is a strong correlation between the two, a patient with a 3-per-second spike-wave complex may exhibit other seizure types, including generalized tonic-clonic seizures. The interpretation of such records should read: “This is an abnormal study because of 3-per-second spike-wave complexes. This is consistent with a seizure disorder of the generalized type.”
Appearance
The 3-per-second spike-wave complex is synchronous from the two hemispheres, with highest amplitude over the midline frontal region. The lowest amplitudes are in the
Table 5-4: Interpretation of generalized spikes.
Type EEG features Clinical features
Burst suppression Bursts of slow waves with superimposed sharp waves, interspersed on periods of relative flattening.
Severe encephalopathy from anesthesia, anoxia, or other diffuse cause.
3-per-second
spike-wave Spike or polyspike complexes at 2.5-4.0/sec. Increased by hyperventilation.
Generalized epilepsy.
May be seen in clinically unaffected relatives.
6-per-second (phantom) spike- wave
Small spike-wave complexes. May have a frontal or occipital predominance.
If frontal, associated with tonic-clonic seizures.
If occipital, usually not associated with seizures.
Hypsarrhythmia High-voltage bursts of theta and delta with multifocal sharp waves
superimposed, interspersed by relative suppression.
Seen in children with infantile spasms.
Slow spike-wave Spike-wave pattern resembling the 3-per- second variety but at 1-2/sec and often with asymmetry and less interhemispheric synchrony.
Lennox-Gastaut syndrome.
Generalized seizures, often tonic, may be atypical absence, atonic, or myoclonic.
temporal and occipital regions. The frequency changes slightly during the course of the discharge, beginning close to 4/sec and declining to 2.5/sec. Immediately following the discharge, the record quickly returns to normal. The spike component may have a double spike or polyspike appearance.
The 3-per-second spike-wave complex is promoted by hyperventilation. If absence epilepsy is considered, the patient should be asked to hyperventilate for 5 minutes instead of the usual 3 minutes. Children with absence seizures become symptomatic if the discharge lasts longer than 5 seconds. During the discharge, the technician should ask the patient a question. The patient with absence seizures often answers after the discharge. The
question and the response should be noted on the record.
The 3-per-second discharge is less well organized during sleep than during the waking state. Its appearance is more polyspike in configuration and the spike-wave interval is less regular.
The spike component is polyspike in some patients. Patients with this polyspike pattern are more likely to exhibit myoclonus.
Clinical correlations
The 3-per-second spike-wave pattern correlates well with primary generalized epilepsy, if the remainder of the recording is normal. Factors which would make the clinical doubt the diagnosis of primary generalized epilepsy include:
Figure 5-6: Three-per-second spike-wave complex
The 3-per-second spike-wave complex which is typical of absence seizures. The spike is actually a polyspike, and the frequency is not constant throughout the discharge, with faster frequency during the early portion of the discharge and slowing somewhat later in the discharge. Left and right medial portions of the LB montage.
• abnormal EEG background • focal discharges
• history of slow neurologic development • abnormal neurologic examination
Treatment of absence epilepsy often abolishes the interictal discharge. This is different from most focal epilepsies in which interictal spiking persists despite good seizure control.
Slow spike-wave complex
The slow spike-wave complex is at 2.5/sec or less. The morphology is less-stereotyped than the 3-per-second spike-wave complex. The duration of the slow spike is usually more than 70 ms, which is technically a sharp wave. The complex is generalized and synchronous across both hemispheres, with the highest amplitude in the midline frontal region.
During sleep, the slow spike-wave complex may be continuous. This activity may not indicate status epilepticus but rather represents activation of the interictal activity with sleep.
The slow spike wave complex is frequently associated with the Lennox-Gastaut
syndrome. It also has been called petit mal variant, but this term is misleading and should not be used. In the Lennox-Gastaut syndrome, the slow spike-wave complex is usually an interictal pattern, but may also be ictal. Since these patients have a mixed seizure
disorder, ictal events may show patterns other than the slow spike-wave complex,. Atonic seizures are characterized by generalized spikes during the myoclonus followed by the slow spike-wave pattern during the atonic phase. Atonic seizures are most characteristic of the Lennox-Gastaut syndrome. Akinetic seizures are characterized by the slow spike- wave discharge throughout the seizure. Tonic seizures occur in Lennox-Gastaut
syndrome and are characterized by a rapid spike activity or desynchronization rather than the slow spike-wave complex.
Fast spike-wave complex
The fast spike-wave complex has a frequency of 4-5/sec and has the appearance of slow waves with superimposed sharp activity, rather than distinct spike-wave complexes. Maximal amplitude is in the fronto-central region.
Patients have
generalized tonic-clonic seizures with or without myoclonus. Absence seizures are rare. This is the most common pattern seen in patients with idiopathic
generalized tonic-clonic seizures. The discharge is not as stereotyped as the 3-per-second spike- wave complex, and the synchrony is less prominent. 6-per second (Phantom) spike-wave complex
The 6-per-second spike-wave complex is characterized by brief trains of small spike- wave complexes which are distributed diffusely over both hemispheres, with a frontal or occipital predominance. They are most common during the waking and drowsy states and disappear during sleep.
The clinical implications of the frontal and occipital rhythms differ. Frontal
predominance is frequently associated with generalized tonic-clonic seizures, whereas occipital predominance is not associated with clinical seizures. Hughes (1980) provided the acronyms WHAM and FOLD. WHAM = waking record, high amplitude, anterior, males. FOLD = females, occipital, low amplitude, drowsy. WHAM is associated with seizures and FOLD is not.
The 6-per-second spike-wave pattern is differentiated from the 14-and-6 positive spike pattern not only by polarity but also by the more widespread distribution and occurrence in wakefulness. Both rhythms may appear in the same patient. The 6-per-second pattern is interpreted as abnormal and the different clinical implications should be emphasized in the report.
Hypsarrhythmia
Hypsarrhythmia is characterized by high-voltage bursts of theta and delta waves with multifocal sharp waves superimposed. The bursts are separated by periods of relative suppression. In some circumstances, flattening of the EEG may be an ictal sign, indicating that there has been sudden desynchronization of the record. [more?]
Figure 5-7: Fast spike-wave complex
Fast (about 6-per-second) spike-wave complex, which is seen in primary generalized epilepsies. Left lateral portion of the LB montage.