Recording the brain's electrical waves via electrodes placed on the scalp. It is the foundational test for diagnosing epilepsy, distinguishing types of seizures, and evaluating disorders of consciousness.
Indication
- Suspected seizure (convulsion) episodes and diagnosis/follow-up of epilepsy
- Differential diagnosis of unexplained loss of consciousness, staring spells, or fainting
- Evaluation after febrile (fever-related) seizures in children
- Investigation of sleep disorders and sleep-related neurological events
- Evaluation of generalized brain dysfunction such as encephalitis or encephalopathy
- Monitoring of unconscious patients in intensive care
- Supportive investigation in the diagnosis of brain death
Preparation
- Wash your hair clean before the procedure; do not use gel, spray, cream, or hair dye
- For some studies you may be asked to sleep less the previous night (sleep-deprivation EEG); follow the instructions
- Continue your regular medications unless otherwise instructed; antiepileptic medications are changed only with physician approval
- Avoid stimulants such as tea, coffee, and cola for 8-12 hours before the procedure
- For children, you may bring a toy or book to encourage cooperation
How it's performed
- Electrode placement points are marked on the scalp and a mild conductive paste is applied
- Typically 19-21 electrodes are placed at specific points; the hair is not shaved
- You lie on your back or sit comfortably; you may be asked to open and close your eyes
- In some segments, deep breathing (hyperventilation) and light flashes to the eyes (photic stimulation) are performed
- A standard EEG takes about 20-40 minutes; sleep or sleep-deprivation EEG may take longer
- At the end of the procedure, the electrodes are removed and the gel is easily washed out of the hair
Post-procedure
- The recording is evaluated by a neurologist; the report is usually ready within a few days
- Results are interpreted alongside the clinical findings and, when needed, MRI or CT imaging
- A single normal EEG does not rule out epilepsy; long-term video-EEG monitoring may be recommended if needed
- You can return to your normal activities immediately after the procedure
- If antiepileptic treatment is started, regular follow-up and a repeat EEG when needed are planned
Risks
- EEG is painless and performed from the skin surface; no electricity is applied to your body — only brain signals are recorded
- Mild skin irritation or redness may rarely occur where the electrodes are placed
- Dizziness and tingling during hyperventilation, and headache during photic stimulation, may occur
- Very rarely, light stimulation or hyperventilation may trigger a seizure in individuals with an existing seizure tendency; the procedure is performed under technician supervision
FAQ
Why am I asked to stay awake for a sleep-deprivation EEG?
Sleep deprivation increases the brain's seizure tendency, making it easier to detect electrical abnormalities that may not appear on a standard EEG. For this reason, a sleep-deprivation EEG can provide more sensitive information when epilepsy is suspected.
If my EEG is normal, does that mean I do not have epilepsy?
No. A single normal EEG does not definitively rule out epilepsy. Findings may appear only during a seizure or under specific conditions such as sleep or sleep deprivation. If clinical findings persist, your physician may request a repeat EEG or video-EEG monitoring.
Will I feel pain or dizziness during or after the EEG?
The procedure is painless. Temporary tingling and dizziness during hyperventilation (rapid breathing), and a mild headache during photic stimulation, can occur. These effects usually subside within minutes.
My child will have an EEG; how can I help so they are not afraid?
The procedure is painless and safe; you can simply explain that the electrodes are 'small stickers that listen to the brain's music.' Bringing a favorite toy or book makes cooperation easier.
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