This lecture is all about the recognition of an abnormal EEG, its characteristics, its appearance and all about how to differentiate the abnormal activity with normal EEG background.

1. Recognition of abnormal EEG
SHEHZAD HUSSAIN
02-FEB-2017

2. Contents
1. Introduction
2. The criteria for being normal or abnormal
3. Factors that affect EEG
4. Frequency
5. Morphology
6. Epileptiform abnormalities
7. Non Epileptiform abnormalities

3. Introduction
Electroencephalograph represents
complex irregular signals that may provide
information about underlying neural activities in the
brain. Since the human brain generates a small yet
measurable amount electrical signal the degree of
activity is measurable. The brain waves recorded
from the scalp have a very small amplitude of
approximately within 100µV. The frequencies of these brain
waves range from 0.5 to 100 Hz, and their
characteristics are highly dependent on the degree
of activity of the brain’s cerebral cortex.

4. Cont.…
The data generated has proven to be particularly useful for the
following purposes:
1) to confirm a clinical suspicion of epilepsy;
2) to identify Epileptiform activity;
3) to document seizures that the patient is unaware of;
4) to evaluate response to therapy;
5) to evaluate nocturnal or sleep-related events;
6) to evaluate suspected pseudo seizures and
7) to evaluate syncope.

5. Factors that affect EEG
• The following factors are the most important for
interpretation of an EEG.
I. Age
II. State
III. Medication
IV. Technical factors
V. Standard setting of machines (filter setting LFF,
HFF, sensitivity etc)
VI. Temperature (specially in low tem <27ċ)

6. Frequency
An electroencephalograph (EEG) represents complex irregular
signals that may provide information about underlying neural
activities in the brain.
Information about waveform frequency and shape is combined
with the age of the patient, state of alertness or sleep, and
location on the scalp to determine significance.
Normal EEG waveforms, like many kinds of waveforms, are
defined and described by their frequency, amplitude, and
location.
For a normal human being, brain waves
can be categorized as one of the four wave groups.

7. Change in frequency;

8. Cont..
The spectra of these waves are:
1. The Delta waves which include all the waves
in the EEG below 3.5 Hz. They occur in deep sleep, in childhood,
and in serious organic
brain disease.
2. The Theta waves have frequencies between
3.5 and 7.5 Hz. These occur mainly during the
childhood, but they also occur during
emotional stress in some adults.

9. Cont..
3. The Alpha waves are rhythmic waves
occurring at a frequency range between 8
and 13.5 Hz, which are found in all normal
persons when they are awake in a quiet,
resting state of cerebration.
The Beta waves are very low amplitude, and high frequency
range between 14 and 30 Hz. They are affected by mental
activity.

10. Morphology:
• By means of morphology we identify the normal
waveforms, including K complex, V waves,
lambda waves, positive occipital sharp transients
of sleep (POSTS), spindles, mu rhythm, spikes,
sharp waves, and certain delta waves (polyphasic
and monophasic shapes).
• These waves are recognized by their shape and
form and secondarily by their frequency. They
include waves that may be normal in some
settings and abnormal in others (eg, spikes, sharp
waves).

12. Slow waves

13. Steps in the analysis of suspected abnormal
transients;
• Is the transient cerebral or artifactual?
• If cerebral, is it normal or abnormal?
• If abnormal, is it specific for epilepsy (epileptiform)?
• If epileptiform, is it focal (or regional, or lateralized) or
generalized?
• If focal or regional, what is the field of the discharge?
Discharges Associated with Epilepsy
• Interictal Epileptiform Discharges
• Seizure Patterns or Ictal Patterns

14. Cont..
• Criteria for epileptiform discharges
• VOLTAGE: high
– MORPHOLOGY: shorter, lower amplitude first phase
– longer, higher amplitude second phase
– polyphasic
– aftergoing slow wave
– different from background
• Polarity: great majority are predominantly surface
negative

17. Cont..
• DURATION: short (but not too short)
• Spike: <70 msec
• Sharp wave: 70-200 msec
• BACKGROUND: abnormal
• Must have a physiologic field
• LOCATION & STATE: unlike normal physiologic transients
Epileptiform Discharges
• Spikes (20-70 msec)
• Sharp waves (70-200 msec)
• Spike-and-wave, Slow-spike-and-wave, Sharp-and-slow-wave, Multiple
spike (Polyspike), Multiple-spike-and-slow-wave (Polyspike-and-slow-
wave) Complexes

18. A- spike; B- sharp wave; C- spike-and-wave complexes; D- sharp-and-slow-wave complexes;
E- slow-spike-and-slow-wave complex; F- polyspike-and-wave complex; G- multiple-sharp-and- slow-
wave complex; H- polyspike complex;
I&J- multiple sharp wave complexes. Even though spikes and sharp waves
usually have after-going slow waves, the term spike-and-wave complex is usually reserved for the
situation where the slow wave is very prominent, higher in voltage than the spike.

19. Ictal vs interictal discharges
• Ictal discharge usually not a repetition of interictal discharges,
except in generalized absence seizures
• Occasional patterns can be either ictal or interictal (spike-and-
wave discharges, paroxysmal fast activity)

20. The non-epileptiform EEG abnormalities in the
context of the neurological disorders;
• When the non-epileptiform abnormalities are seen on an EEG
record, they are not specific for an underlying etiology. In
these situations, however, the EEG provides evidence of
organic electrophysiological dysfunction and the patterns
observed may orientate for the diagnostic possibilities. The
most important types of the non-epileptiform EEG
abnormalities are Focal slow activity - Focal slow activity may
be an indicative sign of focal cerebral dysfunction, especially in
awake adults, and it seems to be the result of a cortex
deafferentation (the interruption or destruction of the afferent
connections of nerve cells) from subcortical structures.

21. Cont…
• It was first described by Walter, in 1936,
who proposed the term "delta waves"
for focal slow activity associated with
tumors involving cerebral hemispheres.
• It is the most common phenomenon
encountered in clinical EEG that is
indicative of a localized structural lesion.
• some cases, focal slow activity may
presents as focal and irregular slow
activity in the delta frequency, receiving
the designation of polymorphic delta
activity (PDA). which is usually due to a
structural lesion or a subcortical
dysfunction (although the anatomic
correlation is not always exact)

22. EEG in Epilepsy Summary;
• The EEG remains the most sensitive and specific
test in support of epilepsy
• There is great potential for over-reading epileptic
abnormalities on EEG
• More damage is done by over-reading than
under-reading
• The EEG should never be a substitute for a
detailed clinical history.

23. The End
Do not disappoint the one whose
hope lies in you.
Hazrat Ali A.S