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EEG

EEG. For Neurology Residents 2009. Not exactly EEG, but…. …things you need to know. Epilepsy and driving. Epilepsy and pregnancy. 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. PART I.

allistair-mckay
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EEG

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  1. EEG For Neurology Residents 2009

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

  3. 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

  4. PART I WHAT IS AN EEG AND HOW IS IT RECORDED?

  5. Recording procedure 20-30 minutes, relaxed patient Eyes opened/closed Photic stimulation, Hyperventilation +/- sleep +/- pain, noise

  6. PART II HOW DO YOU READ AN EEG ?

  7. Why do you need to know this? • Exams • Emergencies • To understand the reports

  8. 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 ?

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

  10. 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?

  11. 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.

  12. The typical EEG

  13. Normal deviations from normal (!) • Drowsiness • Sleep • Age (young and old!) • Activation procedures (a) Hyperventilation (b) Photic stimulation

  14. 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…

  15. Focal slowing

  16. Generalized slowing Ebersole & Pedley

  17. 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”

  18. 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).

  19. 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

  20. Focal epileptic activity

  21. Focal epileptic activity

  22. Terminology “Potentially epileptic abnormality” “Epileptiform abnormality”

  23. Phase Reversal

  24. Non-epileptic phase reversal (normal background activity)

  25. Generalized Inter-ictal Activity Generalized spike and wave

  26. 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

  27. Partial complex seizure with secondary generalization

  28. Neonatal seizure

  29. Neonatal seizure cont…

  30. 3 Hz spike and wave (from Ebersole and Pedley)

  31. Summary • Interictal epileptic activity = spikes and sharp waves • Ictal epileptic activity = evolving rhythmic activity

  32. 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.

  33. 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

  34. Electrode artifact

  35. Eye Movements

  36. EKG Artifact

  37. Head movement artifact during a pseudoseizure

  38. So how do you read an EEG? “Plan and scan” Organized Approach Orient Normal Abnormal Age and State Artifacts Scanning Vertical Horizontal

  39. Scanning

  40. Focal slowing

  41. If all else fails… Describe what you see From Fisch and Spehlmann

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