Recording the Electroencephalogram (EEG)

Recording the EEG

Analyzing EEG Waves Frequency Waveform or morphology Spatial distribution

Beta Alpha Theta Delta Hz Hz Hz Hz 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 EEG The Clinical EEG is of greatest value in:The Clinical EEG is of greatest value in:Epilepsy Coma – atypical or complicated Other disturbances of consciousness of uncertain cause

The study of the EEG remains essential to the diagnosis and treatment of epilepsy –History / Clinical impression is not always 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 Specificity Signature Patterns

3 /sec Spike and Wave – the signature of Typical Absence Seizures 1 sec Onset epileptiform

Hypsarhythmia – the signature of West Syndrome ( Infantile Spasms)

–13 year-old male child Recurrent headaches and fainting.Recurrent headaches and fainting. CT normal, neurologically normal. CT normal, neurologically normal. –Description of fainting episodes: Becomes “quiet”, falls to ground, brief “twitching of limbs”, followed by confusionBecomes “quiet”, falls to ground, brief “twitching of limbs”, followed by confusion First episode Approximately 3 x year.First episode Approximately 3 x year. Family Hx – Younger sibling with seizures.Family Hx – Younger sibling with seizures. –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 classification of epilepsy

13yo male EEG Background Hz 76631P

13yo male Neurology OPD Bipolar recording 76631P

Hx of 4 year-old boy Hx of 4 year-old boy Daily “staring spells” in nursery schoolDaily “staring spells” in nursery school No birth injury or traumaNo birth injury or trauma Neurologically normalNeurologically normal Paternal uncle known with epilepsyPaternal uncle known with epilepsy Referring doctor: ? Absences – typical or otherwise? Absences – typical or otherwise

4 year-old boy, awake75241

Sensitivity of the EEG In what proportion of subjects with epilepsy can the EEG confirm epilepsy?In what proportion of subjects with epilepsy can the EEG confirm epilepsy? 50% positive for epilepsy on recording the f irst routine 20 min EEG. Ways to improve sensitivity: Ways to improve sensitivity: Sleep can increase the yield by further 40%Sleep can increase the yield by further 40% Recording during a period of increased number of seizures or shortly after a seizureRecording during a period of increased number of seizures or shortly after a seizure A negative EEG does not rule out possibility of a seizure disorder.