EEG: What you should know

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Normal sleep

Stages:

NREM (75%):

  • Dreams are not remembered
  • Synchronized.

Stages of NREM:

  1. Stage 1
  2. Stage 2 (45%): Stage having longest duration
  3. Stage 3
  4. Stage 4.

NREM (stage 3 + stage 4) – together called “Deep sleep”.

REM (25%):

  • Dreams are remembered
  • Desynchronized sleep.

 

Waves of EEG:

  • Beta is fastest
  • Delta is slowest.

Normal EEG findings:

  • Eyes open: Beta predominance
  • Eyes closed: Alpha predominance
  • Stage 1 NREM: Theta (vertex) waves
  • Stage 2 NREM = Sleep spindles & K complexes
  • Deep sleep (stage 3 & 4 NREM): Delta wave:
    • Delta: 20-50% → Stage 3
    • Delta: >50% → Stage 4.
  • REM sleep: “Saw tooth” waves.

 

 

Disorders of sleep:

  • Stage 2 NREM: Bruxism
  • Deep sleep (stage 3 & 4 NREM): Night terror, Sleep walking and nocturnal enuresis
  • REM sleep: Nightmare & Narcolepsy.

 

Electrode placement in EEG:

  • Odd electrode is left
  • Even electrode is right
  • Example:
    • O1O3 → Left occipital
    • O2O4 → Right occipital.

 

Generalized vs partial seizure:

  • Partial: Present on one side
  • Generalized: Present on both sides.

Activation techniques:

  1. Intermittent photic stimulation
  2. Hyperventilation (used in absence seizures).

 

Spike and wave discharge:

  • A spike followed by a wave
  • The most characteristic EEG change in epilepsy
  • Types:
Frequency of ‘spike & wave’ Seen in
2 Hz (slow) Lennox-Gastaut syndrome (LGS)
3 Hz Absence seizure
4-6 Hz (fast) Juvenile myoclonic epilepsy

 

Gallery

Lennox-Gastaut syndrome (LGS):

  • Slow spike & wave
  • DOC: Valproate
  • New effective drug: Rufinamide.

Absence seizure:

  • Burst pattern (3 Hz spike & wave)
  • DOC: Ethosuximide.

Burst suppression: Cerebral anoxia

Creutzfeldt-Jakob disease (CJD): Periodic triphasic complexes

Subacute sclerosing panencephalitis (SSPE):

  • Periodic giant waves
  • Delayed and rare CNS complication of measles
  • Drug used: Inosine pranobex.

Herpes encephalitis:

Periodic lateralising epileptiform discharges (PLED): Present only on the affected side.

Hypsarrhythmia:

  • Diffuse giant waves with a chaotic background
  • Like ventricular fibrillation in EEG (you can’t understand anything)
  • Seen in WEST syndrome/ infantile spasm
  • DOC: ACTH
  • Orphan drug: Vigabatrin.

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