Benign EEG Variants And Patterns of Unknown Significance

Yvan Tran, MDSaint 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• 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 rhythmposterior 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

• 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

• 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

• 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