Q 1.32. Electroencephalography (EEG)

1. What is EEG?

• • Electroencephalography (EEG) is a non-invasive diagnostic test that evaluates brain wave activity.
  • It involves placing multiple small, metal electrodes along the scalp to detect electrical changes in the brain.
  • These electrodes pick up signals produced by the brain, which are then recorded by a machine.

2. Purpose and Applications:

• • Diagnosing Epilepsy: EEG helps diagnose epilepsy by detecting abnormal electrical patterns associated with seizures.
  • Other Brain Disorders: It can also identify abnormalities related to other brain disorders.
  • Monitoring Consciousness: EEG is useful for evaluating altered consciousness episodes with uncertain causes.

3. Normal EEG Patterns:

• • The awake EEG typically shows:
    • Alpha waves (8-12 Hz, 50 μV) over the occipital and parietal lobes.
    • Beta waves (>12 Hz, 10-20 μV) frontally.
    • Theta waves (4-7 Hz, 20-100 μV).
  • Abnormalities include:
    • Asymmetries between hemispheres (suggesting structural disorders).
    • Excessive slowing (1-4 Hz, 50-350 μV delta waves) seen in depressed consciousness, encephalopathy, and dementia.
    • Abnormal wave patterns, which may be nonspecific or diagnostic (e.g., epileptiform sharp waves).

4. Activation Techniques:

• • If routine EEG is normal but a seizure disorder is suspected:
    • Hyperventilation, photic stimulation, sleep, and sleep deprivation can help elicit evidence of seizures.
    • Nasopharyngeal leads may detect temporal lobe seizure foci.
    • Video EEG combines video monitoring with EEG to assess seizure types.

5. Continuous Monitoring:

• • Ambulatory EEG (over 24 hours or longer) can determine if memory lapses or episodic motor behavior result from seizure activity.
  • Video EEG is used before surgery to identify epileptogenic foci.

Remember, EEG is a valuable tool in neurology for understanding brain function and diagnosing various conditions.

References:

1 msdmanuals.com

2 med.uth.edu

3 nhs.uk

4 health.harvard.edu