PART III

THE USE OF EEG

EpilepsyPeriodic patterns

Other

1. Epilepsy

1. Yield after single seizure 50% (at best)• higher if done sooner• increases up to 80% with 4th EEG

2. Epileptic abnormalities seen in approx. 0.5% of normals

• 2-14% with migraine, prior trauma, etc…• 5-8% children• 35% siblings of epileptics

3. Poor predictive value

AAN practice parameter Neurology 2007; 69: 1996

4. EEG most useful to classify the epileptic syndrome

International classification of epilepsies

• Localization – idiopathice.g. benign rolandic

• Localization – symptomatic/cryptogenic

e.g. TLE

• Generalized – idiopathice.g. JME

• Generalized – symptomatic/cryptogenic

e.g. Lennox-Gastaut

• Age of onset

• Seizure Type(s)

• Family History

• Exam/Imaging

• EEG

Epilepsia 2001; 42:796.

Epilepsy cont…

King et al. Lancet 1998; 352: 1007

• Syndrome diagnosed clinically in 47%• With EEG, 77%

• EEG within 24hr, 51% vs. 34%

• Initial EEG 43%, after SD-EEG 61%

Epilepsy cont…

• Therefore…use the EEG to classify the epileptic syndrome, not to diagnose seizures

• e.g. TLE vs. JME

2. Periodic Patterns

Stereotypical sharp complexes repeating at a constant time interval for most or all of the

recording.

Periodic

Stereotypical

Sharp

Repeating

Constant time interval

Most of the recording

Rhythmic

• Rhythm = “the regular, measured flow of sound…or action”

• Rhythmic activity can be brief, and is continuous

Hirsch et al. J Clin Neurophysiol 2005

Periodic Patterns cont…

• UNILATERAL

PLEDs, Status

• BILATERAL

• Short latency (<4 sec)

Triphasic waves, periodic complexes (of CJD)

BiPLEDs, Status

• Long latency (>4 sec)

Burst-suppression, SSPE

Alternatively…

• PLEDs

• BiPLEDs

• GPEDs• Status, periodic complexes (CJD), SSPE, burst-

suppression etc…• triphasic waves??

PLEDs

• Considered to be an interictal epileptic pattern (but strongly assoc. with seizures)

• BiPLEDs occur independently over both hemispheres

PLEDs

Same patient (change timescale)

Periodic Complexes of CJD

• Can be biphasic, triphasic etc…

• Can be unilateral initially

• Not seen in nvCJD, FFI, only 10% other genetic CJD, rarely with v/v @ codon 129

• Distinguish from triphasic waves based on clinical context

• Distinguish from PLEDs or status by reaction to stimuli, disappearance with sleep

Periodic complexes in CJD (from Ebersole and Pedley)

Periodic complexes in CJD (poor example)

Triphasic waves

• Toxic-metabolic encephalopathy

• Typical of (but not specific for) hepatic encephalopathy

Triphasic waves (Fisch and Spehlmann)

Triphasic waves

Burst-suppression

Burst-suppression

SSPE

from Ebersole & Pedley)

Status

Chong J Clin Neurophysiol 2005 adapted from Young Neurology 1996

Status

NCSE post-arrest

3. Other

• Coma• Brain death• EEG not indicated in headache*

• Can consider in certain situations (pregnancy

• EEG not useful in syncope• 2003-2007 JGH 517 EEG’s for syncope, LOC, or

fall• 57 abnormal (0 epileptic, 6 potentially epileptic)• Only 5 changed management

*Neurology 1995;45:1263 Neurology 2002;59:490**Arch Int Med 1990;150:2027

PART IV

SLIDESHOW

3 Hz spike and wave with hyper

Focal interictal epileptic activity (right anterior temporal)

Cont… next page

Generalized interictal epileptic activity

Burst-suppression

Cont…next page

Focal seizure (glioma)

PLEDS

(Focal) non-convulsive status

Hypsarrythmia with infantile spasm

BECRS

Burst-suppression post-arrest

Triphasic waves

Periodic complexes in CJD (from Fisch and Spehlmann)

Focal slowing and epileptic activity, patient with sepsis

Independent seizures 37 week HIE Ebersole and Pedley

Cz-C3

Sp1-Sp2

Cz-C4

EOG

Fp1-F7

T5-O1

Fp2-F8

T6-O2

Asystole secondary to a seizure

Cont…next page

PLEDS I year post TBI

REVIEW

TAKE-HOME MESSAGE

1. To read an EEG:

-orient yourself

-have an approach

-describe what you see

TAKE-HOME MESSAGE

2. The EEG is prone to artifact. Findings such as epileptic activity or focal slowing are often a judgement call, and can be seen in normal people. Therefore, the EEG is not absolute.

TAKE-HOME MESSAGE

3. The EEG is not good at diagnosing or “ruling-out” seizures. It is far more useful for correctly classifying the epileptic syndrome.

TAKE-HOME MESSAGE

4. Exam questions will not be subtle (No artifacts, no subtle focal slowing)

REFERENCES

Drury I, Beydoun A. Pitfalls of EEG interpretation in epilepsy. Neurol Clin 1993; 11: 857-81.

Noachtar S et al. A glossary of terms… Electroencephalogr Clin Neurophysiol Suppl 1999; 52: 21-41.

Engel J. A proposed diagnostic scheme for people with epileptic seizures and with Epilepsy: Report of the ILAE Task Force on classification and terminology. Epilepsia 2001; 42: 796-803.

Sundaram et al. EEG in epilepsy: current perspectives. Can J Neurol Sci 1999; 26: 255-62.

Young GB. Metabolic and inflammatory cererbral diseases: electrophysiological aspects. Can J Neurol Sci 1998; 25: S16-S20.

Blume WT. Clinical and basic neurophysiology of generalised epilepsies. Can J Neurol Sci 2002; 29: 6-18.