Frequently Asked Questions (FAQ's)
• What is a Routine EEG?
• What is Sleep Deprivation EEG Testing?
• What is an Ambulatory EEG?
• What are Evoked Potential Recordings?
• What are Visual Evoked Potentials (VEPs)?
• What are Somatosensory Evoked Potentials (SSEP)s?
• What are Brain Stem Auditory Evoked Potentials (BSAEP)s?
• What is an Electroretinogram (ERG)?
• What are NCS and EMG?
The EEG or Electroencephalogram is a recording of electrical brain waves.
We perform routine, sleep-deprived and ambulatory EEGs. Patients of all ages are referred for an EEG for a variety of reasons and the outcome may assist the referring doctor in diagnosis and treatment.
EEG stands for electroencephalogram. It is a recording of the 'brainwaves' - the electrical activity of the brain.
A routine EEG takes approximately 45 minutes - 1 hour.
Clinical physiologists take measurements of your head and small metal discs attached to long wires (electrodes) are then attached.
The test itself is painless.
The recording takes about 20-30 minutes. You will be either lying or sitting during this time. When finished you will be able to return home or to work/school.
Babies, young children, and patients with learning difficulties may be given sedation in the form of a small liquid drink to induce drowsiness and/or sleep so that the patient is still enough to acquire a stable reading. This takes a little longer and you may be here for 2 to 3 hours.
Sleep Deprivation EEG testing is an EEG recording used to record your sleep patterns. In preparation for the test you will be deprived of sleep so that it is likely you fall asleep during the test.
Some EEG changes remain hidden when you are awake and can only be seen when you are drowsy or asleep.
The complete test takes approximately 1.5 hours. You are advised to return home and go to sleep afterwards.
This involves recording tiny electrical signals produced by the brain throughout the day and night. A small lightweight portable recorder is used to record your signals at home during normal routines and natural sleep. For this test we take a continuous recording of your EEG for up to 5 days.
The EEG tests are painless and you will feel nothing during the recording.
There are usually no after effects from the test, but a small number of patients may experience an allergic skin reaction. If you are sensitive to cosmetics, lotions or sticky tape, please inform the clinical physiologist before the test starts. There is no danger to pregnant women or their babies from this test.
We perform Visual Evoked Response (VERs), Brain Stem Auditory Evoked Potentials (BSAEPs), Somatosensory Evoked Potentials (SSEPs) and Electroretinograms (ERGs).
These are recordings of electrical signals produced naturally by your brain following repeated stimulation of the eyes, ears or arms and legs. They provide information on the function of nerve pathways associated with vision, hearing and sensations.
The tests take about an hour, except for the Electroretinogram, which takes about 2-2½ hours to complete.
These are tests of the pathway between the eye and the back of the brain.
You will be asked to look at the centre of a television screen that has a moving black and white chequer board pattern. Each eye is tested separately, with a patch covering the eye not being investigated. This is a painless procedure and there are no after effects.
When finished you will be able to return home or to work/school.
These are tests of the pathways from the arm or leg through the spinal cord to the brain. An electrical stimulator is used to pass brief electrical currents to your nerves. This can be uncomfortable, but not be painful. There are no after effects.
Please inform the Clinical Physiologist if you have a pacemaker.
These test the pathways from the ears. Headphones are used to give a clicking sound to one ear and a continuous noise to the other ear.
This is a painless test and there are no after effects.
This is a test of the electrical activity from the eye. It is usually necessary to have a very fine metal fibre placed along the lower eyelid for this test. You will usually have to be in the dark for 20-30 minutes during the test and you will also be asked to look at flashing lights of different colours and brightness.
The eye drops used will give you blurred vision for a few hours after the test.
Please bring a pair of sunglasses to help reduce glare from bright light. You must not drive home and preferably come accompanied.
There are no other side effects to the test.
What is NCS?
NCS stands for Nerve Conduction Studies. These studies measure how long it takes for a nerve impulse to travel along a nerve. If the nerve is trapped, damaged or diseased the signals will be altered.
Following some NCS, Electromyography (EMG) may need to be performed.
This is a test that records the electrical activity naturally produced in your muscles.
You may have one or both of these tests. The tests are used to investigate a number of different muscle and nerve problems and it will assist your consultant in his diagnosis and management of your complaint or condition.
The doctor performing the test will explain the procedure before starting.
What do the tests involve?
NCS: A number of sticky tabs (electrodes) are placed on the hands or feet.
A small electrical pulse is given to the skin, and a measurement taken. This is repeated at 2 or 3 points along the arm or leg.
EMG: A fine needle is inserted into a muscle. Recordings are taken with the muscle relaxed and when the muscle is tensed. This takes a few minutes for each muscle.
Who will perform the test?
A Clinical Physiologist or a doctor will perform NCS. A doctor performs EMG.
Will I feel anything?
NCS: Most people say that the electric pulse is not painful, but that they feel an unusual sensation such as tingling or pulsing.
EMG: A fine needle is used for this test, and, although a sharp scratch is felt as the needle is inserted, the majority of our patients do not consider this test to be unduly uncomfortable.
How long will the test take?
NCS: Approximately 30 minutes.
EMG: Approximately 20-30 minutes but very occasionally longer.
If you require both NCS and EMG the test may take up to 1 hour.
Are there any after-effects following the test?
NCS: No.
EMG: The muscles tested may feel sore for a short time after the examination.
After both tests you will be able to continue your daily activities as normal.
These tests are not a treatment but will help the doctor to understand the reasons for your symptoms.
Are there any risks?
Please tell the doctor if you have a heart pacemaker but it is usually still safe to have the test.
NCS: There are no reported risks.
EMG: The small size of the needle means that it should not be too uncomfortable. The needle may cause a small amount of bleeding, some bruising and soreness.
When will my consultant get the results?
Your consultant should have the results as soon as possible.