This presentation looks at the benign or non-epileptiform variants in EEG, their characteristics and identification. Examples of the common benign variants are provided in the presentation.

1. Non-epileptiform variants in EEG
Dr Pramod Krishnan
Consultant Neurologist and Epileptologist
Manipal Hospital, Bengaluru

2. Classification
Epileptiform Pattern Rhythmic Pattern
• Normal Slowing during
Hyperventilation
• RMTD/ RTTD
• SREDA
• Midline Theta Rhythm (Ciganek)
• Frontal Arousal Rhythm
• Slow or fast Alpha Variant
• Mu rhythm
• Small Sharp Spikes (SSS)
• POSTS, Lambda
• Wicket Spikes
• 6 Hz spike and wave bursts
(WHAM and FOLD)
• 4Hz Vertex Rhythm
• Breach Rhythm
• 14Hz and 6Hz positive bursts

3. Benign Epileptiform Transients True Epileptiform Transients
Superimposed or merging with the
background
Stand out distinctly from the background
Positive or negative polarity in average
referential montage
Negative polarity in average referential
montage
Usually of low amplitude Usually of high amplitude
After coming slow wave is absent After coming slow wave is usually present
Does not disturb the background Usually disturbs the background
Often seen in awake or drowsy state,
disappears in sleep
Often becomes frequent in sleep.
No single feature can distinguish the two. But collectively they can be useful in
separating spikes from benign transients.

4. Positive Occipital Sharp Transients of Sleep
(POSTS)
• Seen in 50-80% of a healthy adult population.
• Occur in late stage 1 NREM sleep (deep drowsiness) and persist into
NREM 2 and NREM 3 sleep.
• Rarely or never seen in REM sleep.
• Positive polarity sharp wave with phase reversal at O1 or O2.
• Common in adolescents, young adults and through middle age.
• Rare below 3 years and above 70 years of age.

5. Average referential montage showing a train of POSTS (black marks) which are monophasic or
diphasic positive waves with symmetric rising and falling phases.

9. POSTS
• Usually bilateral; 1/3rd asymmetric.
• Amplitude: 20- 75 μV (upto 120 μV)
• Duration: 80- 200 ms.
• POSTS may occur as individual transients, or in trains of up to four to
six POSTS per second.
• The trains typically last about a second and rarely last more than 2
seconds.
• Absent in blind and severely amblyopic individuals.

10. Lambda Waves
• Seen in children and adults, in awake state.
• Located in the occipital regions, diphasic with positive polarity.
• Same morphology and distribution as POSTS, but in awake state.
• Triangular/ saw tooth shape, generally symmetric.
• Amplitude: 50 microV
• Duration: 100-250 msec
• Present with eyes opened and evoked by visual scanning.
• Associated with POSTS and photic driving response.

12. Lambda waves
• Presence or absence of lambda waves is not abnormal.
• Asymmetry suggests abnormality on the side of lower amplitude.
• Each lambda wave is preceded by a scanning eye movement, usually
recognizable as an eye movement artefact.
• Lambda waves partly represent visual evoked potentials, but not
necessarily in response to light.
• It can be seen with movements in the dark, so may be related to other
processes.

13. EEG longitudinal bipolar montage showing triangular shaped waves in the occipital channels which are
Lambda waves.. They are associated with horizontal eye movements which are seen in both frontal
anterior temporal channels. .

14. Benign Epileptiform Transient of Sleep (BETS)
• Small Sharp Spikes that occur in NREM 1 or 2 sleep.
• Mono or diphasic (rarely tri- or quadriphasic).
• Low amplitude (<50 uv) and brief duration (< 65 ms).
• Sometimes followed by a waveform in the theta or alpha range
mimicking a spike and wave.
• Widespread horizontal dipole distribution in the absence of any
disruption of background activity.

15. • Difficult to localize precise and may appear in both hemispheres either
independently or bisynchronously.
• They frequently demonstrate an opposite polarity in the anterior to
posterior direction in a single hemisphere or, when they occur
bisynchronously, transversely between hemispheres.
• They rarely repeat with the same distribution and morphology more
than once per 0.5s.
Benign Epileptiform Transient of Sleep (BETS)

19. MU Rhythm
• Arch-shaped waves at 7-11 Hz in central or centro-parietal regions.
• Seen in young adults.
• Occur in trains of a upto a few seconds.
• Often appear at different times on the two sides of the head.
• As it is a focal activity it is better seen in bipolar montages.
• Mu waves have a similar frequency as Alpha rhythm; it is usually best
recognised when the Alpha rhythm is blocked by eye opening.

21. EEG longitudinal bipolar montage: Rhythmic, arch-shaped waves of around 12Hz activity noted
over the central regions (right > left) lasting 6 sec. Better seen by blocking alpha by eye opening.

22. EEG average referential montage: Mu rhthm seen in C3 and C4 (better seen in bipolar montage as it
is a focal activity). Often appear at different times on the two sides of the head.

23. Mu rhythm
• The appearance of Mu rhythm is facilitated while a subject scans visual
images.
• It is blocked by voluntary, reflex, or passive movement, by the intention
to move, or by tactile stimuli.
• The effect is greatest over the hemisphere opposite the side of the
movement or stimulation.
• Frequent trains of mu rhythm only on one side, or a consistent
asymmetry of amplitude or frequency of mu rhythm suggests an
abnormality on the side of the lower amplitude or frequency.

25. Phantom spike-wave (6 Hz spike-wave)
• Consists of 4 to 7 Hz repetitive spike-wave complex with relatively low
amplitude (< 40 uV) fast spike (< 30 ms) followed by a 5-7 Hz wave of
equal or greater amplitude.
• Each burst usually appears in a bisynchronous fashion, of < 1 sec.
• Occurs during drowsiness or during eye closure at rest.
• Seen in young adults.

28. WHAM and FOLD
1. FOLD: In Female, Occipital (maximal over the posterior head
regions), Low amplitude spike, seen in Drowsiness.
2. WHAM: In Wakefulness, High amplitude spikes (but the spike
amplitude is lower than the intervening waves), Anterior (frontally
dominant), in Males.
• Association of WHAM type with seizures increases if: the repetition
rate is < 5 Hz, the spikes are much greater in amplitude than the
intervening slow waves, and if it persists into sleep.

29. FOLD

30. FOLD

31. WHAM

32. 14 and 6 Hz Positive Bursts (ctenoids)
• Consists of brief runs (< 1 sec) of positive spikes of 14 or 6 Hz.
• It may appear as a:
1. 14- and 6-Hz positive spike complex
2. 14-Hz positive spikes alone (older children and adolescents)
3. 6-Hz positive spikes alone (early childhood, adults).
• Amplitude rarely exceed 75 uV.
• It occurs either bisynchronously or unilaterally (usually involving both
hemispheres at different times)
• It is most likely to occur during sleep.

33. An example of 14- and 6-Hz positive spike bursts in an 8-year-old boy. Note burst of positive spikes in left temporo-
occipital region.

35. 14 and 6 Hz Positive Bursts
• It is best seen in ear reference montages (long inter-electrode distance).
• Maximum amplitude over the posterior temporal head regions.
• Seen in comatose patients with acute hepatic failure like Reye’s
syndrome, other metabolic and post-anoxic encephalopathies and head
trauma.
• In these conditions the frequencies is more variable, relatively low in
amplitude and the burst can be elicited by alerting stimuli.

36. wickets

39. wickets

40. Wicket Waves
• Trains of arch shaped 6-11Hz spikes, resembling Mu rhythm.
• Sharp monophasic, no slow wave
• Negative polarity, with amplitude of upto 200 uV.
• Usually anterior or mid-temporal regions (can occur anywhere).
• Occurs in individuals whose background activity contains sharply
contoured waveforms.
• Present in relaxed wakefulness, drowsiness, light sleep.
• Usually in middle and late adulthood.

41. EEG longitudinal bipolar montage: Rhythmic, around 12Hz activity noted over the right temporal
region lasting 1 sec or less, without any disruption of the background.

42. EEG average referential montage: Rhythmic, around 12Hz activity noted over the right temporal
region lasting 1 sec or less, without any disruption of the background.

44. (A) Right temporal spike-wave in a patient with Rt MTLE-HS and CPS. Unlike Wicket, the spike-
wave occurs in isolation without a buildup of arciform waveforms.
(B) Wicket: rhythmic 6-Hz activity, occurring in brief bursts, maximal over the left temporal area.
A
B

45. Rhythmic mid-temporal theta of drowsiness (RMTD
or RTTD)
• Trains of rhythmic theta waves (4-7 Hz) lasting upto a few seconds.
• Waves often have a flat top, or notched by a 10-12 Hz component.
• Often begin and end with a gradual increase and decrease of
amplitude, but the overall frequency remains stable (unlike ictal
rhythms).
• Occur in the mid-temporal regions, on one side or both (independently
or simultaneously, with shifting asymmetry).
• Present in young adults during light sleep and drowsiness.

46. EEG longitudinal bipolar montage: rhythmic mid-temporal 5Hz activity lasting 3 seconds. EEG
suggests drowsy state. The waves may have a flat or notched top. Begins and stops gradually.

47. EEG average referential montage: rhythmic mid-temporal 5Hz activity in a drowsy patient. Occur
in mid-temporal region, unilaterally or bilaterally (as in this patient).

48. Posterior Slow Waves of Youth (PSWY)
• Occurrence, distribution, reactivity are like Alpha waves.
• Occur between 2-21 years of age, most common at 8-14 years of age,
but can occur at any age.
• Each waveform has the duration of 3 to 6 alpha waves combined.
• May occur in rapid succession or be separated from each other by one
to several seconds.
• Have a characteristic fused Alpha wave morphology in which individual
Alpha waves appear with increasing definition during the second half
of the waveform.

49. EEG longitudinal bipolar montage: Normal posterior alpha rhythm of 9 Hz, interspersed with slow
waves with a duration of 5-6 alpha waves, which attenuates along with the alpha rhythm.

51. EEG average referential montage: Normal posterior alpha rhythm of 9 Hz, interspersed with slow
waves, which attenuates on eye opening and appears on eye closure (like the alpha rhythm).

52. EEG average referential montage: Normal posterior alpha rhythm of 8-9 Hz, interspersed with
posterior slow waves of youth. They can be isolated or occur in rapid succession.

53. EEG longitudinal bipolar montage: Posterior slow waves are seen with alpha rhythm appearing to
emerge out of the PSWY in the second half of the wave (fused alpha wave morphology).

54. EEG longitudinal bipolar montage: Delta range waveform seen over the right occipital region,
persisting into drowsiness, suggesting presence of an underlying structural cause.

55. Subclinical rhythmic EEG discharge of adults
(SREDA)
• Occurs mainly in elderly, during wakefulness (rarely in sleep), during or
shortly after hyperventilation.
• Occurs several times in a single recording, and in subsequent
recordings.
• No evolution in frequency, morphology or distribution.
• Preserved consciousness and no post-ictal changes on EEG.
• Maximal over parietal and posterior temporal regions.
• In 2/3rd cases, it is bisynchronous and symmetrical (less often
unilateral, asymmetric).
• Duration of 40-80 s, upto 5 minutes.

56. • It typically begins abruptly, or is delayed for several seconds after a
single high amplitude sharp or slow wave.
• Once established, the pattern consists of repetitive monophasic sharp
waves (150-300 ms duration) that repeat every 1-2 sec and evolve into a
sustained sinusoidal 4-7 Hz pattern (usually 5-6 Hz).
• It may end abruptly, or gradually diminish and merge with the
background.
• In most cases it replaces the ongoing background activity.
Subclinical rhythmic EEG discharge of adults
(SREDA)

58. SREDA observed after TGA. 1-2 Hz rhythmic sharp transient pattern, distributed diffusely, but more prominent over
the anterior temporal and mid-temporal areas.

59. Paroxysmal hypnogogic hypersynchrony
• Occurs in normal children in drowsiness or arousal from sleep.
• It consists of low amplitude spikes intermixed with rhythmical
moderate to high amplitude 3-5 Hz bisynchronous bursts.
• The spike like components most often take the form of a simple
notching of the slow waves or are irregularly intermixed with the slow
waves giving an appearance of multiple spike complexes.
• A distinguishing feature of the irregularly intermixed spike
components is the superimposed appearance and inconsistent time
relationship between the spikes and the slow waves.

61. Midline Theta Rhythm of Ciganek
• Rhythmic train of 5-7Hz (6Hz)
• Duration: <20sec
• Smooth, sinusoidal, arch-like, spiky appearance (>50uV)
• Amplitude waxes and wanes
• Vertex (Cz)
• Fz > Pz >> parasagittal electrodes
• Wakefulness (concentration) and drowsiness
• Children and adults
• Not associated with epilepsy

62. Midline theta rhythm of Ciganek: Longitudinal bipolar montage showing waxing and waning
sharp theta activity over midline electrodes, with phase reversal across Cz.

63. Midline theta rhythm of Ciganek: Average referential montage shows maximum amplitude of the
burst at Cz. It occurred during a period of arousal.

64. Breach Rhythm
• The skull is a high frequency and high voltage filter.
• A skull defect (due to any cause) creates a low resistance pathway for
EEG currents.
• This results in a localized increase in beta activity directly or near the
skull defect.

65. EEG Longitudinal bipolar montage of 28 year lady showing breech rhythm over the right
hemispheric region, with prominent beta activity.

66. EEG Longitudinal bipolar montage in the same patient showing breech rhythm, with prominent
beta and higher amplitude discharges over the right hemispheric region.

67. Normal slowing during hyperventilation
• Bilateral synchronic delta activity
• Most prominent in the frontal area
• Generally in persons up to 30 years old
• Disappears after around 30 seconds after hyperventilation was stopped
• Prolonged slowing during hyperventilation has no pathologic meaning
(sometimes is hypoglycemia the cause)
• The lack of this response has no pathologic meaning
• ORIDA during hyperventilation is normal in children, however not in
adults.

68. THANK YOU