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Benign EEG Variants And Patterns of Unknown Significance

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  1. Benign EEG Variants And Patterns of Unknown Significance Yvan Tran, MD Saint Mary’s Epilepsy Program 4/27/13

  2. No Disclosures

  3. Learning Objectives • Understanding the importance of identifying benign variants • Understanding the broad categories of benign variants • Age predisposition for benign variants

  4. 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.

  5. Benign Variants • Benign Patterns can be divided into two groups: • Rhythmic Patterns • Patterns with Epileptiform Morphology

  6. Benign Variants With Rhythmic Patterns • Rhythmic Theta Burst of Drowsiness (RMTD) or Psychomotor Variant • Alpha Variant • Midline Theta Rhythm • Frontal Arousal Rhythm

  7. 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.

  8. 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

  9. Rhythmic Theta Burst of Drowsiness Ernst Niedermeyer, Fernando H. Lopes da Silva. Electroencephalography: basic principles, clinical applications, and related fields. 2005

  10. 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

  11. Slow Alpha Variant Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.

  12. 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

  13. Midline Theta Rhythm Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.

  14. 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

  15. Frontal Arousal Rhythm Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.

  16. 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

  17. 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

  18. 14-and-6 Hz Positive Bursts Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.

  19. 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

  20. Small Sharp Spikes Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.

  21. 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

  22. Six Hertz Spike and Wave Burst Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.

  23. 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%

  24. Wicket Spikes Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.

  25. 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

  26. Breech Rhythm Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.

  27. Patterns of Unknown Significance • Subclinical Rhythmic Electrographical Discharge of Adults (SREDA)

  28. 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

  29. SREDA Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.

  30. Wicket Spikes Santoshkumar et al. Clin Neurophysiol 2009; 120:856-61

  31. SREDA Ebersole. J., Pedley T. Current Practice of Clinical Electroencephalography. 2003.

  32. Six Hertz Spike and Wave Burst Santoshkumar et al. Clin Neurophysiol 2009; 120:856-61

  33. 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

  34. 14-and-6 Hz Positive Bursts Santoshkumar et al. Clin Neurophysiol 2009; 120:856-61

  35. Rhythmic Theta Burst of Drowsiness

  36. 14-and-6 Hz Positive Bursts Ernst Niedermeyer, Fernando H. Lopes da Silva. Electroencephalography: basic principles, clinical applications, and related fields. 2005

  37. RMTD Santoshkumar et al. Clin Neurophysiol 2009; 120:856-61

  38. Small Sharp Spikes Richard, L. INTRODUCTION TO SLEEP ELECTROENCEPHALOGRAPHY

  39. Wicket Spike Richard, L. INTRODUCTION TO SLEEP ELECTROENCEPHALOGRAPHY

  40. Six Hertz Spike and Wave Burst Ernst Niedermeyer, Fernando H. Lopes da Silva. Electroencephalography: basic principles, clinical applications, and related fields. 2005