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How To Interpret an EEGHow

To

Interpret

an EEG and its Re p ort p

Marie Atkinson, MD

Assistant Professor of Neurology

WSU School of Medicine/DMCWSU

School

of

Medicine/DMC

Comprehensive Epilepsy Program

July 19, 2010

What is an EEG?What

is an EEG?

An EEG is a scalp recording of brain

An EEG is a scalp recording of brain wave activity. • The brain wave activity recorded is a summation of the inhibitor y and y excitatory post synaptic potentials that occur across a neuron membraneoccur across a neuron membrane

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That's all good but how the heck do I

read an EEG!? • First know what you are looking at on the screen. • 1. Montages • Electrodes • Channels

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B Montage

A Montage

aka Bi p olar Monta g e pg aka referential montage -Different Montages allow you to see different things

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things

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Bipolar Montage

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A Montage

Z-P Montage

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Z-T Monta

g e g

Z-C Montage

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2. Sensitivity

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7.5 microvolts

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2.0 microvolts

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30.0 microvolts

SensitivitySensitivity

The gist whatever voltage you decideThe

gist whatever voltage you decide to read at will see waveforms at that voltage or highervoltage or higher • The lower the voltage the more you will seesee • Read at the voltage that allows you to see the waveforms the best •Usuall y at 7.5 microvolts

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y 3

Filters

3

Filters

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LF (Low Frequency) FilterLF

(Low

Frequency)

Filter

The gist... whatever number you set it up at,The

gist... whatever number you set it up at, the EEG will not amplify any frequencies b elow that number.

Ex. LF filter set at 1.0Hz will not show onEx.

LF filter set at 1.0Hz will not show on

EEG any waves with a frequency below

1.0Hz.

Usually LF filter is set at

1.0Hz

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Usually

LF filter is set at 1.0Hz

HF (High Frequency) FilterHF

(High

Frequency)

Filter

Just the opposite of LF filter EEG will

Just the opposite of LF filter EEG will not display any frequencies above this di td bd es i gna t e d num b er. • Usually set at 35Hz

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Notch (60Hz) FilterNotch

(60Hz)

Filter

Special filter that sharply cuts off any

Special

filter that sharply cuts off any activity at 60Hz and above.

Current through plugs often is at 60Hz,Current

through plugs often is at 60Hz,
allows you to get rid of outside artifact by other machinery in roomother machinery in room

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Enough of the technical, can we please

learn how to read the EEG!

Break it down into steps:Break

it down into steps: 1 kdAii ill 1 .Bac kg roun d A ct i v i t y gi ves y ou an overa ll sense of what is going on with the patient.

2. Symmetry- is there any focal changes seen.

3. Sta

g e of alertness g

4. Abnormality - slowing, sharp waves,

triphasics seizure PLEDs etc

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triphasics seizure PLEDs etc

BackgroundBackground

Gives you a sense of how the patient isGives

you a sense of how the patient is doing

Best evaluated in posterior channel usually

Best evaluated in posterior channel usually occipital

Pi h h l d

P at i ent h as to h ave e y es c l ose d - 4 different frequencies: delta, theta, alpha, and beta

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Background FrequenciesBackground

Frequencies

Delta (marked slowing)Delta

(marked slowing) -1-3Hz

Th t ( ildl l )

Th e t a m ildly s l ow -4-7Hz • Alpha (normal back g round) - 8-13Hz • Beta (barbituates/benzos) >13Hz

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Delta FrequencyDelta

Frequency

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Theta FrequencyTheta

Frequency

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Beta FrequencyBeta

Frequency

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Normal EEGNormal

EEG

Normal background activity (alpha

Normal

background activity (alpha frequency) • No abnormalities (nothing stands out in the back g round g) • No changes in the EEG provoked by photic hyperventilationphotic hyperventilation • No assymmetry

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Asymmetries

Asymmetric SlowingAsymmetric

Slowing

Seen with focal lesions surgery etc

Seen with focal lesions surgery etc • Easy to see with A montage • Can be unmasked with hyperventilation or photic stimulationor photic stimulation

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Right Hemisphere SlowingRight

Hemisphere

Slowing

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PLEDsPLEDs•

Stands for

Periodic Lateralized Epileptiform

Stands

for

Periodic

Lateralized

Epileptiform

Discharges"

Occurs throughout the entire EEG at aOccurs

throughout the entire EEG at a frequency of 1-2Hz

Only in one hemisphereOnly

in one hemisphere • Seen usually in acute lesions (stroke, bleed, etc), postictal, Herpes Encephalites, CJD, etcetc), postictal,

Herpes

Encephalites,

CJD, etc • Controversy over what they mean, nonconvulsive status or not?

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nonconvulsive status or not?

PLEDsPLEDs

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A Little Aside on PLEDsA

Little

Aside on PLEDs • The Boards/RITE exam loves PLEDs•Usuall y on these tests the answer is either CJD or y,

Herpes Encephalites

• How to distinguish for exam,CJDusually associated withmyoclonus,moresubacute• Herpes Encephalitesusually associated withfever and more acute

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and more acute

Partial (focal) Status EpilepticusPartial

(focal)

Status

Epilepticus

Status involving one hemisphere

Status

involving one hemisphere • Patient may still be able to converse, appear awake during this type of seizure •Don t necessaily need to treat this type of Don t necessaily need to treat this type of seizure with anesthetics.

Ndt ilt tbf

N ee d t o aggress i ve l y t rea t b e f ore becomes secondarily generalized Status.

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Partial Status EpilepticusPartial

Status

Epilepticus

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Abnormalities

1. Epileptiform Activity

Epileptiform ActivityEpileptiform

Activity

Means the EEG reader saw some abnormalitesMeans

the EEG readerquotesdbs_dbs35.pdfusesText_40

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