Procedure

Electroencephalogram

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Electroencephalogram, EEG

  • Background
  1. Mechanism
    1. Measures electrical activity of cerebral cortex via sampled electrodes placed over the surface of the scalp
    2. Measures gray matter function (Neuronal function)
    3. Normal in white matter disease
    4. Often combined with video to correlate abnormal CNS electrical activity with movement and behavior
  2. Availability
    1. Historically most EEG and Video EEG testing is performed in formal centers staffed by technicians
    2. Home EEG monitoring (including video EEG) have become more readily available
      1. Only small studies available, but efficacy make approach inpatient systems
        1. Brunnhuber (2020) Epilepsia 61(Suppl 1):S3-S10 +PMID: 32683686 [PubMed]
      2. Home and Ambulatory Devices
        1. MobileMedTek Electro Tek
        2. Seer Home and Ambulatory Video EEG-ECG
        3. Samar (2023) Am Fam Physician 108(5): 517-8 [PubMed]
  • Findings
  • Brain Wave Types
  1. Beta Waves
    1. Frequency >13 Hz
    2. Fine, medium amplitude wave form
    3. Seen in an alert patient
  2. Alpha Waves
    1. Frequency 8-13 Hz
    2. Seen in a quiet but awake patient or during REM Sleep
    3. Low amplitude wave form
  3. Theta Waves
    1. Frequency 4-7 Hz
    2. Seen in drowsy patients
  4. Delta Waves
    1. Frequency <4 Hz
    2. Seen in deep, non-REM Sleep patient
  • Findings
  • Pathologic Brain Waves
  1. Flat Line
    1. Seen in brain death, as well as some Medication Overdoses
  2. Diffuse Slowing
    1. Organic brain syndrome or post-ictal state
  3. Localized Slowing
    1. Focal neurologic lesion
  1. Indications
    1. Seizure Diagnosis
    2. Anticonvulsant weaning
      1. Seizure free for 2 years and
      2. Normal EEG
  2. Non-Seizure Times
    1. Abnormal in 70% of Seizure patients
  3. During Generalized Tonic Clonic Seizure
    1. Massive electrical discharge with high frequency, high amplitude waves
  4. During Focal Seizure
    1. Localized Seizure activity
  5. During Petit Mal Seizure
    1. Spike and Dome wave pattern
  6. Post-ictal
    1. Slowing of EEG
  7. Medications that do not affect EEG
    1. Anticonvulsants
  8. Medications that cause Beta (fast wave patterns)
    1. Barbiturates
    2. Benzodiazepines
  1. Cortical CVA (large vessel disease)
    1. Abnormal EEG
  2. Subcortical or Brainstem CVA (small vessels disease)
    1. Normal EEG
  • Findings
  • Metabolic encephalopathy
  1. Non-focal slowing of EEG
  2. Rhythmic bursts of symmetrical frontal slowing
  3. Specific patterns may assist with etiology
    1. Hepatic Encephalopathy: Triphasic waves