For Neurology Residents EEG For Neurology Residents 2009

Not exactly EEG, but… …things you need to know. Epilepsy and driving. Epilepsy and pregnancy

I. What is an EEG and how is it recorded ? 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

WHAT IS AN EEG AND HOW IS IT RECORDED? 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 Orient yourself. Is there normal brain activity present or is it altered ? Is there abnormal activity present ? What is the state ? Is it age – appropriate ? Are there any artifacts present ?

1. ORIENT YOURSELF Montage (bipolar or referential) F7, F8 Time scale Sensitivity (amplitude, positive/negative) Other channels (EKG, EOG)

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 1-3 Hz Theta 4-7 Hz Alpha 8-12 Hz Beta > 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 (!) Drowsiness Sleep Age (young and old!) Activation procedures (a) Hyperventilation (b) Photic stimulation

Background abnormalities Slowing (theta or delta) 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

“Disturbance of the background activity” 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” Spike, patting artifact, spike

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 = 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 v-waves, 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 Scanning 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