EEG
For Neurology Residents
2009
Not exactly EEG, but…
…things you need to know.
1. Epilepsy and driving.
2. Epilepsy and pregnancy
OUTLINE
I. What is an EEG and how is it recorded ?
II. How do you read an EEG ?
III. The use of EEG
IV. Slideshow/Quiz
PART I
WHAT IS AN EEG AND HOW IS
IT RECORDED?
Recording procedure
20-30 minutes, relaxed patient
Eyes opened/closed
Photic stimulation, Hyperventilation
+/- sleep +/- pain, noise
PART II
HOW DO YOU READ AN EEG ?
Why do you need to know this?
• Exams
• Emergencies
• To understand the reports
An organized approach
1. Orient yourself.
2. Is there normal brain activity present or is
it altered ?
3. Is there abnormal activity present ?
4. What is the state ?
5. Is it age – appropriate ?
6. Are there any artifacts present ?
1. ORIENT YOURSELF
Montage (bipolar or referential)
Time scale
Sensitivity (amplitude, positive/negative)
Other channels (EKG, EOG)
F7, F8
2. Is there normal brain activity or is
it altered?
• Is the stuff that is supposed to be there
actually there ?
• Is there evidence of a structural lesion or a
toxic/metabolic process that has altered
the normal EEG background activity?
Normal brain activity
• Waves:
Delta
Theta
Alpha
Beta
1-3 Hz
4-7 Hz
8-12 Hz
> 12 Hz
• Posterior dominant alpha rhythm with eye
closure.
• Alpha rhythm ≠ alpha frequency
• Low amplitude, frontal Beta activity.
The typical EEG
Normal deviations from normal
(!)
1.
2.
3.
4.
Drowsiness
Sleep
Age (young and old!)
Activation procedures
(a) Hyperventilation
(b) Photic stimulation
Background abnormalities
• Slowing (theta or delta)
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•
•
•
•
Focal or diffuse
Bilaterally synchronous or not
Rhythmic vs. irregular/polymorphic
High vs. low amplitude
Intermittent vs. continuous
• Can be more subtle
• Attenuation of amplitude
• Asymmetry of alpha
Etc…
Focal slowing
Generalized slowing
Ebersole & Pedley
Summary
• Focal slowing
= rule out structural lesion
• Generalized rhythmic slowing
= consider deep structural lesion or
destructive process
• Polymorphic generalized slowing
= very nonspecific
“Disturbance of the background activity”
3. Abnormal activity
Is there any stuff there that should not be
there at all ?
Not simply alteration of the background
Usually, we are asking if there is epileptic
activity (interictal or ictal).
Focal Inter-ictal activity
•
•
•
•
•
•
•
Spikes and sharp waves !
Phase reversal
Recurrent and consistent
With a field
Followed by slow wave
Asymmetrical
Not explained by artifact
Focal epileptic activity
Focal epileptic activity
Terminology
“Potentially epileptic abnormality”
“Epileptiform abnormality”
Phase Reversal
Non-epileptic phase reversal (normal background activity)
Generalized Inter-ictal Activity
Generalized spike and wave
Ictal Activity (Seizures)
• Electrographic lasts > 10 sec
• Seizures not defined by single pattern;
spikes, spike and wave, slowing,
attenuation etc…
• Rhythmic activity that changes with time
Partial complex seizure with secondary generalization
Neonatal seizure
Neonatal seizure cont…
3 Hz spike and wave (from Ebersole and Pedley)
Summary
• Interictal epileptic activity
= spikes and sharp waves
• Ictal epileptic activity
= evolving rhythmic activity
4. State
• 4 Sleep stages, plus REM
1. Lose α, slow EOM, v-waves
2. Spindles, K-complex, v-waves
3. Delta < 50%
4. Delta > 50%
REM: -looks normal (i.e. awake), need EOG, EMG etc…
• Sleep onset
• Most consider stage 1 sleep = drowsiness
• But…some define sleep onset as appearance of vwaves, others as sleep spindles.
Don’t Forget…
5. Age
• Prior to birth, continuous evolution of EEG
• Posterior-dominant rhythm by 6-12 months;
alpha frequency by 4-8 years
6. Artifacts
• EKG or pulse
• Eye movement
• Electrode
• Muscle/movement
• Electrical
• Weird and wonderful
Electrode artifact
Eye Movements
EKG Artifact
Head movement artifact during a pseudoseizure
So how do you read an EEG?
“Plan and scan”
Organized Approach
Orient
Normal
Abnormal
Age and State
Artifacts
Scanning
Vertical
Horizontal
Scanning
Focal slowing
If all else fails…
Describe what you see
From Fisch and Spehlmann