Variants are the EEG patterns that look like abnormal but considered as normal under given circumstances.

1. Benign EEG Variants
Prepared by
Faizan Abdullah
NPS Trainee technologist
Aga Khan University Hospital Karachi Pakistan
21-09-2020

2. CONTENT
1.Introduction
2.Types of benign variants
3.Rhythmic EEG variants
I. Alpha variant.
II. Mu rhythm.
III. Rhythmic temporal theta burst of drowsiness (“psychomotor variant”).
IV. Subclinical rhythmic electrographic (theta) discharges in adults (SREDA).
V. Midline theta rhythm.
4.Epileptiform EEG variants
I. 14 and 6HZ positive spikes
II. Wicket spikes
III. Small spike sharps (SSS)
IV. 6HZ phantom waves
5.Lambda and lambdoids
I. Lambda waves
II. Posts pr lambdoids
III. Slow lambdoids
6.Age related variants
I. Hypnogogic and hypnopompic hypersynchrony
II. Posterior slowing of youth
III. Temporal theta in elderly
7.References

3. Introduction
Variants are the EEG patterns that look like
abnormal but considered as normal under
given circumstances.

4. Types of variants
• 1. Rhythmic patterns.
• 2. Epileptiform patterns.
• 3. Lambda and lambdoids.
• 4. Age-related variants

5. RHYTHMIC VARIANT PATTERNS
• Alpha variant.
• Mu rhythm.
• Rhythmic temporal theta burst of
drowsiness (“psychomotor variant”).
• Subclinical rhythmic electrographic (theta)
discharges in adults (SREDA).
• Midline theta rhythm.

6. Alpha Variants
• Described first by Goodwin in 1947. There are two types of alpha variants, "slow” and
“fast.”
• The slow (sub harmonic) alpha variant appears as an abrupt, usually has a bifurcated
configuration rhythm and half the frequency of the patient’s more typical waking
background rhythm, and often of greater voltage.
• The fast (harmonic) ….“double” the frequency of the patient’s more typical waking
background rhythm, appearing as beta activity.
• The fast alpha variant rhythm can be induced by hypnotic or anxiolytic medications such
as barbiturates or benzodiazepines .
• Alpha variants behave like alpha rhythm and occurs less than 1% of the normal adult
population

7. Slow (sub harmonic) alpha variant

8. Alpha Squeak effect:
 The first few seconds after closing the eyes might produce an alpha rhythm that
is slightly faster than in other resting and eyes closed state.
 The frequency of the PDR should not be calculated during thisperiod.

9. Mu rhythm
• Also named as “comb” or “wicket rhythm,” or “rhythme rolandique en
arceau
• This waveform is recognized easily and has no pathological significance.
• The mu waveform occurs in the central regions in the awake patient with
the frequency of 9-11 Hz.
• Mu is usually observed bilaterally with shifting predominance; it may,
however, be asymmetrical and asynchronous. Exclusively lateralized mu
should raise a suspicion of an abnormality in the hemisphere …… mu
activity.
• Often in the alpha range frequency, it has rounded positive aspects on 1
side and sharpened negative aspects on the other.
• It is not blocked by eye opening
• It becomes obvious when the alpha disappears (i.e., alpha blocking)
• The most classical feature of mu waveform is that it blocks with motor
activity of the contralateral body.

12. Rhythmic Temporal Theta Bursts of
Drowsiness (“Psychomotor Variant”)
 Gibbs et al. called this pattern the “psychomotor variant” because it was
thought to represent a temporal lobe or psychomotor seizure.
 But discarded because this pattern is observed in asymptomatic healthy
individuals and exhibits poor correlation with patients with true temporal
lobe or psychomotor seizures.
 Also called “rhythmic mid-temporal discharges” describing its …. mid-
temporal head regions, but can spread parasagittally.
 This pattern may be present in waking or early drowsiness and usually in
tracings of adults and adolescents. It wanes with deepening sleep. As its
name implies, this particular pattern
 5- to 7-Hz rhythms in bursts or trains lasting often longer than 10 s and
sometimes beyond a minute. often sharply contoured, monomorphic; it
does not evolve significantly in frequency or amplitude, as occurs in most
ictal patterns.
 Rhythmic mid-temporal discharges can occur bilaterally or independently
with shifting hemispheric predominance.

16. SREDA
• This variant pattern involves sharply contoured 5- to 7-Hz
activities with a wide distribution, mainly over temporo-parietal
derivations.
• It is usually bilateral, but can be asymmetrically disposed.
• can appear as repetitive monophasic sharp waves or as a single
discharge of sharp waves that gradually accelerate to form a
sustained, rhythmic train of theta activity. This may last from 20
s to several minutes, usually 40 to 80 s.
• Because of its duration and evolution, SREDA can easily be
misinterpreted as an ictal pattern
• SREDA is more typically seen in older adults (older than 50
years), and more common at rest, drowsiness, or during
hyperventilation.

18. Midline theta rhythm
• The midline theta rhythm is most prominent at Cz
but may spread to nearby contacts.
• This 5- to 7-Hz frequency exhibits either a smooth,
arc-shaped (mu-like) or spiky appearance.
• Duration.. Variable, tends to wax and wane, more
common in wakeful and drowsy states
• Reacts variably to limb movements, alerting, and/or
eye opening.
• Now regarded to be a nonspecific variant, although
initially it was considered a marker of an underlying
epileptic tendency.

19. MIDLINE THETA

20. 2. EPILEPTIFORM VARIANT PATTERNS
There are 4 major types of Epileptiform
variant patterns:
• 14- and 6-Hz positive bursts.
• Small sharp spikes (benign Epileptiform
transients of sleep [BETS]).
• 6-Hz spike and wave (phantom spike and
wave).
• Wicket spikes.

21. FOURTEEN AND SIX HZ ACTIVITY
• comb-shaped positive spikes maximum at the
posterior temporal/occipital electrodes with a
frequency of 13 to 17 Hz and/or 5 to 7 Hz,
mostly consisting of 14 Hz and/or 6 Hz. .
• Seen during drowsy or light sleep.
• Well seen on contralateral ear referential
montage .
• It occur independently over both sides.
• Best seen in the age group of 13-14yrs.

22. 14 & 6 Hz SPIKES in
longitudinal bipolar montage

23. Common average montage

24. Contralateral mastoid or ear reference
montage

27. • Resemble mu or wicket rhythm seen in the central
region but they occur in the temporal electrodes.
• Appear as brief (<1 s) bursts at 6 to 11 Hz in a
crescendodecrescendo form of sharply contoured
alpha or sharp activity.
• They are predominantly seen in adults older than 50
years.
WICKET SPIKES:

28. Cont’d
• When wicket spikes occur in isolation, they may be mistaken
for an epileptiform discharge. Several features help
differentiate isolated wicket spikes from pathological spikes.
A similar morphology of the isolated wicket spike to those in a
later train or cluster argues for the variant pattern and against
an epileptiform discharge. The absence of a following slow-
wave argues for the variant and against an epileptiform
discharge. An unchanged background also argues more for the
variant and against an epileptiform event.

29. WICKET SPIKES

30. Longitudnal bipolar montage

32. Common average montage

33. WICKET SPIKES

34. Small Sharp Spikes/BETS
• As these names imply, small sharp spikes or benign epileptiform transients of
sleep (BETS) are low in amplitude (~50 µV) and brief (~50 ms).
• Their morphology can be monophasic or diphasic. When diphasic, the ascending
limb is quite abrupt and the descending limb slightly less so They may exhibit a
subtle following slow wave.
• BETS are isolated and sporadic.
• They appear during drowsiness and light sleep in adults.
• They are usually unilateral but can appear independently (and rarely
synchronously) from bilateral regions.

35. Cont’d
 .Other distinguishing features BETS and epileptiform activity are that BETS
do not run in trains, distort the background, or coexist with rhythmic slowing,
and BETS diminish with deepening sleep, whereas epileptiform discharges
worsen with deeper sleep stages.

37. • 6Hz spike and wave (Phantom spike and wave):
• These occur as bursts of miniature spike and wave complexes or runs of
such complexes at 6 Hz rather than the usual 2-4 Hz.
• Their significance is debated, but generally those occurring in the
posterior head regions are regarded as benign.
• Seen at all ages (but especially in adults) they often are confused with 14-
and 6-Hz waves and may merge into them.

38. Phantom spike has further two variants as,
WHAM
wake high amplitudes anterior dominant in males.
FOLD
female occipital low amplitude in drowsiness.
Differentiate wicket spikes from epileptiform spikes:
1. The absence of slow waves following and a preserved background favor
wicket spikes.
2. An equal rise and decay of the sharp waveform also favors a wicket
spike.

39. FOLD

41. WHAM

44. LAMBDA WAVE
• A Normal EEG pattern.
• They resemblance to the Greek lowercase letter lambda ( ) so called lambda
waves.
• Positive waves
• Seen over the occipital region when patient is looking at a picture of pattern.
• It blocks on eye closing or looking at white card.
• They have a duration of 160 to 250 ms, an amplitude of 20 to 50 µV, and
usually appear over bi-occipital leads, although occasionally may be unilateral

45. •

48. Positive occipital sharp transients of sleep or
Lambdoid
• Normal EEG pattern
• Morphologically they are surface positive potentials
• They are seen maximum at 01-02 leads.
• They are seen during drowsiness.
• POSTS are usually synchronous but can be asymmetric in
size. There are most commonly seen between 15 and 35 yr
of age, and usually in light sleep.

49. ------

51. Slow lambdoids
• Slow lambdoids of youth, also known as cone-shaped
waves or O-waves, are high voltage, diphasic slow
transients seen over the occipital contacts and frequently
with the occipital delta activity in deeper sleep states
• As the name implies, they are cone-shaped. They can be
seen up to 5 yr of age.
• OTHER NAMES ARE
1.RHO WAVES,
2. CONE SHAPED WAVES
3.O WAVES
4.SLOW LAMBDOIDS OF YOUTH

53. Age related variants
Posterior slow waves of youth, also called youth waves, posterior fused
transients, and sail waves, are triangular, 2- to 4-Hz waveforms that coexist with other
waking background rhythms.
Less prevalent toward the age of 20 years but could be seen as late as 25 years of age.
Distinguish between normal and abnormal posterior delta :
(a) disproportionately high amplitude as compared to the alpha rhythm (>1.5 times the
voltage of the alpha rhythm or >200 μV),
(b) serial rhythmic waveform which constitutes OIRDA (Occipital Intermittent
Rhythmic Delta Activity
(c) widespread distribution involving the central or midtemporal electrodes,
(d) predominantly unilateral.
(e) persistent after eye opening.

54. Posterior slow waves of youth

55. Temporal theta in the elderly
It is a commonly encountered age-dependent pattern. This is a 4- to 5-Hz activity
involving temporal channels and is thought by some to represent a subharmonic
of the 8- to 10-Hz background rhythm common in the asymptomatic elderly
individuals. However, this rhythm is distinct from the alpha rhythm in that it
persists with eye opening and even into drowsiness and light sleep.
Hyperventilation augments this pattern’s voltage and persistence.
Some have observed them to be more prevalent over the left hemisphere. Their
significance remains controversial.

56. HYNOGOGIC and HPYNOPOMPIC
• Synchronous high voltage theta, delta at
beginning of sleep
• < 2 yrs of age
• May be notched and/or have a spiky
component only occurs at transition phase.
• Reverse phenomena could also in opposite
phase which is hypnopompic response.

57. HYPNAGOGIC HYPERSYNCHRONY

58. REFERENCES
1.EEG PRIMER
2.PRECTICAL GUIDE FOR EEG BY YAMADA THORU AND ELIZEBTH MENG