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Benign EEG Variants And
Patterns of Unknown
Significance
Yvan Tran, MD
Saint Mary’s Epilepsy Program
4/27/13
• No Disclosures
Learning Objectives
• Understanding the importance of identifying
benign variants
• Understanding the broad categories of benign
variants
• Age predisposition for benign variants
Significance of Benign Variants
• Understanding what is normal is just as important as
picking up abnormal discharges.
• Overinterpreting can lead to improper diagnosis with
longer term consequences for patients.
• Important to look at the discharges in the context of
the background activity.
• These variants can be seen in normal individuals or
in patients with various complaints but has not been
proven directly to indicate an increased
epileptogenic risk.
Benign Variants
• Benign Patterns can be divided into two groups:
– Rhythmic Patterns
– Patterns with Epileptiform Morphology
Benign Variants With Rhythmic Patterns
• Rhythmic Theta Burst of Drowsiness (RMTD) or
Psychomotor Variant
• Alpha Variant
• Midline Theta Rhythm
• Frontal Arousal Rhythm
Rhythmic Theta Burst of Drowsiness
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Also known as RMTD or psychomotor variant
Seen in drowsiness
Bursts of rhythmic theta waves of 5-7 Hertz
Waves are notched or flat topped due to
superimposition of faster frequencies on the
background
• Maximal in the midtemporal leads but can spread
parasagittally
• Can be seen bilaterally or shift independently from
side to side.
Rhythmic Theta Burst of Drowsiness
• Confused for epileptiform discharges due to the
gradual increase and decrease of amplitude
seen with the train of discharges.
• Waves are usually monomorphic
• Seen in 0.5%-2% of patients
Rhythmic Theta Burst of Drowsiness
Ernst Niedermeyer, Fernando H. Lopes da Silva. Electroencephalography:
basic principles, clinical applications, and related fields. 2005
Alpha Variant
• Same distribution as the normal background
rhythmposterior quadrants
• Is a harmonic of the normal alpha rhythm
– Slow alpha variant
• A subharmonic with frequencies between 4-5 Hz
• Often notched
– Fast alpha variant
• A supraharmonic with frequencies between 16-10 Hz
• Pattern is reactive
• Seen in the relaxed awake state
• Often alternates with the normal alpha pattern
Slow Alpha Variant
Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.
Midline Theta Rhythm
• Focal rhythm over the central leads, usually
maximal at Cz
• Arciform appearance between 5-7 Hz
• Pattern waxes and wanes
• Present during wakefulness and drowsiness
• Reactive pattern including with limb movements
Midline Theta Rhythm
Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.
Frontal Arousal Rhythm
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Seen in children upon arousal
Bursts last up to 20 secs
Frequency of 7-20 Hz
Often waveforms are notched due to varying
harmonic activity
• Resolves once full wakefulness is achieved
Frontal Arousal Rhythm
Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.
Benign Variants With Epileptiform
Morphology
• Fourteen and Six Hertz Positive Bursts
• Small Sharp Spikes (SSS)
• Six Hertz Spike and Wave Burst (Phantom Spike
and Wave)
• Wicket Spikes
• Breech Rhythm
14-and-6 Hz Positive Bursts
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Aka 14-and-6 Hz Spikes
Seen during drowsiness and light sleep
Usually seen in 3-20 y/o, peak at 13-14 y/o
In trains of arch-shaped waves of alternating with
positive spiky waves with rounded negative waves
• Duration is 0.5-1 sec
• Maximal over the posterior temporal regions
• Best seen on referential montage with shifting
lateralization
14-and-6 Hz Positive Bursts
Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.
Small Sharp Spikes (SSS)
• Aka Benign epileptiform transients of sleep (BETS) and benign
sporadic sleep spikes.
• Seen during drowsiness and light sleep
• Seen in adults
• Low voltage averaging <50µV with a duration of <50ms
• Can be monophasic or diphasic
• Can be confused for epileptiform activity due to the occasional
aftergoing slow wave
• Seen best in temporal and ear lead with derivation of long
interelectrode distance.
• They do not occur in trains and decrease with deeper stages of sleep
• Seen in 20-25% of patients
• Can be seen bilaterally or independently
Small Sharp Spikes
Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.
Six Hertz Spike and Wave Burst
• Aka Phantom Spike and Wave
• Duration is usually 1-2 secs
• Seen in adolescents and adults during relaxed
wakefulness and drowsiness
• Seen in 2.5% of patients
• Pattern is usually diffuse and synchronous bilaterally
• Two variants:
– FOLD (female occipital predominant low amplitude and
drowsiness)--more benign variant
– WHAM (wake high amplitude anterior predominant in
male)—possible associated with seizures
• Waveforms tend to disappear in sleep
Six Hertz Spike and Wave Burst
Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.
Wicket Spikes
• Clusters or trains of monophasic arciform
waveforms similar to the Greek mu (µ), however can
occur single waveform
• Not associated with an aftergoing slow wave or
disruption of the background
• Seen during drowsiness and light sleep
• Seen in the temporal regions bilaterally or
independently with shifting lateralization
• Frequency is 6-11 Hz at 60-200 µV
• Seen in adults >30 y/o at incidence of 0.9%
Wicket Spikes
Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.
Breech Rhythm
• High voltage activity of 6-11 Hz seen in regions
overlying a skull defect.
• Seen best over the central and temporal regions
• Voltage is affected by the presence or absence
of bone, bone reabsorption and region of skull
defect.
• Beta activity is enhanced
Breech Rhythm
Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.
Patterns of Unknown Significance
• Subclinical Rhythmic Electrographical Discharge
of Adults (SREDA)
Subclinical Rhythmic Electrographical
Discharge of Adults
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Fairly uncommon
Seen in individuals usually greater than 50
Seen in resting and drowsy states
Increased or precipitated by hyperventilation
Rhythmic theta and delta waves that are sharply contoured
and typically evolve into a rhythmic frequency of 5-7 Hz.
Usually seen in a generalized pattern with predominance over
the parietal and posterior temporal regions; At times can be
lateralized.
Range is 20 secs to several minutes, Mean is 40-80 secs
Abrupt onset
Waves are monophasic
SREDA
Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.
Wicket Spikes
Santoshkumar et al. Clin Neurophysiol 2009; 120:856-61
SREDA
Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.
Six Hertz Spike and Wave Burst
Santoshkumar et al. Clin Neurophysiol 2009; 120:856-61
Wicket Spike
Krauss GL, Abdallah A, Lesser R, Thompson RE, Niedermeyer E. Clinical and EEG
features of patients with EEG wicket rhythms misdiagnosed with epilepsy.
Neurology 2005;64:1879-1
14-and-6 Hz Positive Bursts
Santoshkumar et al. Clin Neurophysiol 2009; 120:856-61
Rhythmic Theta Burst of Drowsiness
14-and-6 Hz Positive Bursts
Ernst Niedermeyer, Fernando H. Lopes da Silva. Electroencephalography:
basic principles, clinical applications, and related fields. 2005
RMTD
Santoshkumar et al. Clin Neurophysiol 2009; 120:856-61
Small Sharp Spikes
Richard, L. INTRODUCTION TO SLEEP ELECTROENCEPHALOGRAPHY
Wicket Spike
Richard, L. INTRODUCTION TO SLEEP ELECTROENCEPHALOGRAPHY
Six Hertz Spike and Wave Burst
Ernst Niedermeyer, Fernando H. Lopes da Silva. Electroencephalography:
basic principles, clinical applications, and related fields. 2005