What is a Routine EEG?
The Electroencephalogram (EEG) is a recording of electrical activity produced by the brain. We perform routine, sleep-deprived, ambulatory and video telemetry EEGs in adults and routine, sleep-deprived and sedation EEGs in children. Patients are referred for an EEG for a variety of reasons and the outcome may assist the referring doctor in diagnosis and treatment. A routine EEG appointment takes approximately 45 minutes - 1 hour.
The neurophysiological scientist takes measurements of your head with a tape measure. A blue or red pencil will be used to mark these measurements. Electrodes (small metal discs attached to long wires) are then attached to these marks with sticky paste. You will feel the skin on your head being rubbed with a cotton bud before the electrodes are attached. There can be up to 21 electrodes all together and it can take around 20 minutes to set up. The EEG recording is painless and takes around 20-30 minutes. You will also have your heart monitored (ECG) at the same time via sticky pads on your hands or arms. For the majority of the test you will be asked to relax with your eyes closed, either in a lying or sitting position. You will be asked to open and close your eyes at various times during the test and may be asked to carry out some deep breathing (hyperventilation) and look at a flashing light (photic stimulation). When finished, the electrodes are removed from the head (they come off easily and painlessly) and the majority of the paste is removed with warm water. Any remaining paste can be washed out with shampoo on your return home.
Babies and young children 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 EEG reading. This takes a little longer and you may be here for 2 to 3 hours. Very rarely an adult patient may require sedation.
What are the side effects of an EEG?
There are no after effects of this test. We cannot read your mind or thoughts. No electricity or needles are used. We only record the signals produced naturally by the brain. The test is an investigation, not a treatment. In the unlikely event you have a seizure during the test, you will be checked over to make sure that you are well enough to go home. If you hold a driving licence you will be obliged to inform the DVLA (as for all the attacks) as this may affect your ability to drive. Please keep this in mind before you agree to undergo the EEG, particularly when asked to look at a flashing light or perform deep breathing for several minutes, as this can, in a very small number of cases, cause a seizure. Your consent for this may be withdrawn at any time. Very rarely there may be an allergic skin reaction where the sticky paste and discs are applied. If you are sensitive to cosmetics, lotions or sticky tape please inform the scientist at the start. For patients who are in pregnancy, there is no significant risk to mother or unborn baby. The benefits of undergoing the test, including the deep breathing, outweigh the risks.
When will I get my results?
EEG recordings are analysed by the Neurophysiological Scientist and, if necessary, a Neurophysiology doctor. A report is prepared for whoever referred you for the test. This process takes a little time and the result of the investigation will not be available to you on the same day.
What is a Sleep Deprived EEG?
A sleep deprived EEG is an EEG recording of 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. You will be told in advance if you are to have this type of recording. A sleep deprived EEG can sometimes be very helpful as some EEG changes remain hidden when you are awake and can only be seen when you are drowsy or asleep. The complete test takes no longer than 1.5 hours. You are advised not to drive to or from the department, and to have someone accompany you back home afterwards.
What is Ambulatory EEG monitoring?
An ambulatory EEG is the continuous recording of the brains' electrical signals throughout the day and night, for up to 5 days. A small, lightweight, portable recorder is used to record your brain wave signals at home during your normal daytime routine, and in natural sleep. The recorder is placed in a small pouch bag and fastened around the waist.
Like the routine EEG, an ambulatory EEG is painless and you will feel nothing during the recording. However, due to the longer recording time, the electrodes have to be secured onto the scalp with specially designed glue. If you are pregnant, or there is a chance you could be pregnant, please inform the Neurophysiological Scientist prior to the investigation. A small number of patients may experience an allergic skin reaction. If you are sensitive to cosmetics, lotions or sticky tape, please inform the neurophysiological scientist before the test is started.
At the end of the recording the electrodes are removed with a specially designed solution which dissolves the glue. There is a chance that flakes of dried glue will remain on the scalp and hair but this will eventually wash and comb out without damage.
What is Video Telemetry EEG?
Video telemetry is a continuous 5 day EEG with video recording. This investigation requires you to stay in hospital as an in-patient for the duration of the investigation. The test is carried out in a specially adapted side room on the Neurology ward where you are monitored 24/7 whilst the recording takes place. As with other long term EEG monitoring the electrodes are temporarily secured with specially designed glue. During your stay you may be sleep deprived or have your medication reduced.
What are Evoked Potential Recordings?
We perform Visual Evoked Response (VERs), Electroretinograms (ERGs) and occasionally Electro-Oculograms (EOGs), Brain Stem Auditory Evoked Potentials (BAEPs) and Somatosensory Evoked Potentials (SSEPs). These are recordings of electrical signals produced naturally by your brain following repeated stimulation of the eyes, ears, arms or legs. Several electrodes are applied to the scalp as in the EEG recording above. 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 take between 1 and 3.5 hours to complete.
What are Visual Evoked Potentials (VEPs)?
This test investigates the nerve 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, there are no after effects and when finished you will be able to return home or to work/school.
What are Somatosensory Evoked Potentials (SSEPs)?
This test investigates the nerve pathways from the arm or leg through the spinal cord to the brain. An electrical stimulator is used to pass small, brief electrical currents to your nerves. This can be a little uncomfortable but not painful. There are no after effects. Please inform the Clinical Physiologist if you have a pacemaker.
What are Brain Stem Auditory Evoked Potentials (BSAEPs)?
This test investigates the nerve pathway from the ears. Headphones are used to deliver a clicking sound to one ear at a time whilst a continuous noise is delivered to the other ear not being tested. This is a painless test and there are no after effects.
What is an Electroretinogram (ERG)?
This test studies the electrical activity from the eye and requires a very fine fibre to be placed along the lower eyelid. Anaesthetic eye drops are used so that you cannot feel this. You will be placed first in the light and then in the dark for 30 minutes and then asked to look at flashing lights of different brightness in a globe. Some special eye drops will be needed to dilate your pupils and 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 once you have left the department. You must not drive home and preferably come accompanied. There are no other side effects to the test.
What are nerve conduction studies (NCS) ?
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 carried out during your visit. The tests are used to investigate a number of different muscle and nerve problems and it will assist your consultant in the diagnosis and management of your complaint or condition. The scientist and /or doctor performing the test will explain the procedure before starting.
What do NCS and EMG tests involve?
NCS (nerve conduction studies) involves a number of sticky tabs (electrodes) which are placed on the skins' surface of the hands or feet. A small electrical pulse is given to the skin and a measurement is taken. This is repeated at 2 or 3 points along the arm or leg.
EMG (Electromyography) involves a very fine needle 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 these tests?
A neurophysiological scientist or a consultant neurophysiologist will perform NCS. The consultant neurophysiologists perform EMG.
Will I feel anything?
For NCS, most people say that the electric pulse is not painful but that they feel an unusual sensation such as tingling or pulsing. EMG testing involves a very fine needle and although a brief 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 takes approximately 30- 45 minutes . EMG testing takes approximately 20-30 minutes but very occasionally longer can last about 1 hour. If you require both NCS and EMG the test may take up to 1.5 hours.
Are there any after-effects following the test?
There are no after effects from NCS. After EMG the muscles which were 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 telephone us, when you receive your appointment letter, if you have a heart pacemaker. Also tell the doctor when you arrive for your appointment. You may require cardiac monitoring during the investigation; however this is not often required and there are no reported risks. During 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. Please inform the consultant if you are taking any anti-coagulant medication; e.g. Warfarin, Aspirin, Clopidogrel and Apixaban.
When will my Consultant get the results?
Your consultant should have the results as soon as possible.
