Recording the Electroencephalogram (EEG)Recording the Electroencephalogram (EEG)

Recording the EEGRecording the EEG

Analyzing EEG WavesAnalyzing EEG Waves

FrequencyFrequency

Waveform or Waveform or morphologymorphology

Spatial distributionSpatial distribution

Beta

Alpha

Theta

Delta

76479

64279

64727

75245

12.5 - Hz

8 -12 Hz

4 - 7 Hz

0.5 - 3Hz

23 Hz

9 Hz

6.5 Hz

1.7 Hz

EEG Frequency Bands

Factors That Determine Whether an EEG Feature is Normal or Abnormal

• Patient Related:

– Age

– State of consciousness

Usefulness of the EEGUsefulness of the EEG

•The Clinical EEG is of greatest The Clinical EEG is of greatest value in:value in:

EpilepsyEpilepsy

Coma – atypical or complicatedComa – atypical or complicated

Other disturbances of Other disturbances of consciousness of uncertain causeconsciousness of uncertain cause

The study of the EEG remains essential The study of the EEG remains essential to the diagnosis and treatment of to the diagnosis and treatment of

epilepsyepilepsy

– History / Clinical impression is not History / Clinical impression is not always clearalways clear• Fit, faint or “funny turn” ?Fit, faint or “funny turn” ?• Focal or generalisedFocal or generalised• Idiopathic / symptomatic / syndromicIdiopathic / symptomatic / syndromic

EEG Patterns and their SpecificityEEG Patterns and their Specificity

Signature Patterns

3 /sec Spike and Wave – the signature of Typical Absence Seizures

1 sec1 sec

Onset epileptiformOnset epileptiform

Hypsarhythmia – the signature of West Syndrome ( Infantile Spasms)

– 13 year-old male child13 year-old male child• Recurrent headaches and fainting.Recurrent headaches and fainting.• CT normal, neurologically normal. CT normal, neurologically normal.

– Description of fainting episodes:Description of fainting episodes:• Becomes “quiet”, falls to ground, brief Becomes “quiet”, falls to ground, brief

“twitching of limbs”, followed by confusion“twitching of limbs”, followed by confusion• First episode 2005. Approximately 3 x year. First episode 2005. Approximately 3 x year. • Family Hx – Younger sibling with seizures.Family Hx – Younger sibling with seizures.

– Can EEG help to confirm a Sz disorder?Can EEG help to confirm a Sz disorder? • If so, ? generalized or focalIf so, ? generalized or focal• Idiopathic / symptomatic ?Idiopathic / symptomatic ?

Usefulness of the EEG in the diagnosis and Usefulness of the EEG in the diagnosis and classification of epilepsyclassification of epilepsy

13yo male EEG Background

10 -11 Hz

76631P

13yo male Neurology OPD Bipolar recording 76631P

Hx of 4 year-old boyHx of 4 year-old boy

•Daily “staring spells” in nursery Daily “staring spells” in nursery schoolschool

•No birth injury or traumaNo birth injury or trauma

•Neurologically normalNeurologically normal

•Paternal uncle known with Paternal uncle known with epilepsyepilepsy

Referring doctor:Referring doctor:

•? Absences – typical or ? Absences – typical or otherwiseotherwise

4 year-old boy, awake 75241

Sensitivity of the EEGSensitivity of the EEG• In what proportion of subjects with In what proportion of subjects with

epilepsy can the EEG confirm epilepsy?epilepsy can the EEG confirm epilepsy?50% positive for epilepsy on recording the 50% positive for epilepsy on recording the ffirst routine 20 min EEG.irst routine 20 min EEG.

Ways to improve sensitivity:Ways to improve sensitivity:• Sleep can increase the yield by further Sleep can increase the yield by further

40%40%• Recording during a period of increased Recording during a period of increased

number of seizures or shortly after a number of seizures or shortly after a seizureseizure

A negative EEG does not rule out A negative EEG does not rule out possibility of a seizure disorder.possibility of a seizure disorder.