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Electromyogram
(EMG) / Nerve Conduction Velocity (NCV) Studies
Here are some common Questions and Answers commonly asked about EMG and
NCV studies:
1. What Can be Learned From an EMG?
The electromyogram studies the electrical characteristics of nerves and
muscles. This information can show injury or disease of the nerves
and muscles. For example, if you have back pain because a
"slipped disc is pinching a nerve," the EMG can tell which
nerve it is, how bad it is, and sometimes even how long it has been
pinched. This helps your physician in managing your problem either
medically or surgically.
2. How is an EMG Done?
The EMG is done with tiny needle electrodes. These are inserted
into selected muscles, depending on your particular problem. The
pins (electrodes) are so tiny that they are not very
uncomfortable. Some patients can't even feel them, but the amount
of discomfort associated with them is different in each patient.
(Everyone has a different level of pain feeling and tolerance).
Any discomfort you may experience during the EMG is temporary, and the
EMG will not make your pain problem worse.
3. What are Nerve Conduction
Velocity Studies? Nerve conduction is done by
giving a very small amount of electrical current to a nerve and it
measures how fast the current travels in the nerve. If the nerve
is sick or injured the current travels slowly and this helps figure out
which nerves are affected. This test is not painful.
4. What Side Effects Can I Expect?
One of the reasons why an EMG is so frequently ordered by physicians is
that it gives a lot of helpful information with a very small risk of
side effects. The most common side effect is a bruise which can
occur if the physician happens to bump a vein in the skin with the
pin. Infections due to bacteria or viruses being carried by the
pin into the body are possible, but exceedingly rare. The EMG will
not make you drowsy or cause reactions since nothing is injected
through the pin.
5. Can I Have This Done if I am
Pregnant? Yes.
6. Do Drugs Interfere with the EMG?
Almost never. Please tell the doctor what drugs you are on at the
time of the examination.
7. Can I drive After an EMG?
It does not affect your ability to drive.
8. Does the EMG Have a Therapeutic
Value? Some patients do report that their pain is
less afterwards, but EMG is not a treatment and should not be confused
with acupuncture.
9. Can I go Back to Work After an
EMG? The EMG does not affect your work status.
Chemodenervation
Procedure
Chemodenervation procedure is done to decrease muscle spasms,
and twitching including facial twitching. A small amount of
medicine (Botox or Myobloc) is injected, usually under EMG control, into
specific muscles. The effect of the procedure lasts for about
three to four months. The procedure is usually very well tolerated
and has minimal side effects.
Tensilon Test
A Tensilon Test is one of the tests done to diagnose Myasthenia
Gravis. A small amount of Tensilon (Edrophonium) is injected
intraveniously under controlled environment and improvement in the
muscle strength is noted.
Another test done to diagnose Myasthenia Gravis is with a repetitive
nerve stimulation test. In this test, a nerve is stimulated at
specified intervals and decremental response is measured.
Blink Reflex Study
This study is done to find out the cause of facial weakness and
pain. It can also be used to find out the prognosis in Bells
Palsy. It is also used for evaluation of more generalized nerve
disorders.
Visual
Evoked Potential (VEP) Study
VEP's evaluate the visual nervous system from the eyes to the occipital
(visual) cortex of the brain. Electrodes are applied to the scalp,
and the patient is usually asked to stare at a pattern on a video screen
while remaining fully alert. Each eye is tested separately.
It is most commonly done to diagnose Optic Neuritis and Multiple
Sclerosis.
Somatosensory
Evoked Potential (SSEP) Study
SSEP's assess pathways from nerves in the arms or legs, through the
spinal cord to the brainstem or cerebral cortex. Electrodes are placed
on the scalp and along the spinal cord, and a small electrical current
is then applied to the skin overlying nerves on the arms or legs.
The current creates a tingling sensation but is not painful. Each
leg or arm is tested separately. It is most commonly done to study
spinal cord function.
Brainstem
Auditory Evoked Potential (BAEP) Study
The BAEP assists in evaluating the auditory nerve pathways from the ears
through the brainstem. Electrodes are attached to the scalp and
earlobes, and earphones are placed over the ears. The phones
deliver a series of clicks or tones to each ear separately. It is
most commonly done to study hearing, brainstem tumors and dizziness.
Electroencephalogram
(EEG) Study
An EEG records the electrical activity of the brain. Highly
sensitive monitoring equipment records the activity through electrodes
that are placed at measured intervals on a patient's scalp.
For the patient, the test is not painful. The head is measured and
the electrodes are placed on the scalp with a paste-like
substance. The test itself usually takes about 90 minutes, and the
principal role of the patient is simply to remain still, relaxed and
comfortable. During the test, the patient may be asked to take
repeated deep breaths (hyperventilate) and may be shown a strobe light
that flashes at different speeds. Both activities can help reveal
different brain patterns that are useful for diagnosis. Sometimes,
physicians also want to observe brain patterns that occur during
sleep. For sleep tests, the patient may be asked to stay awake
most of the night prior to the EEG appointment or in some cases may be
given a mild sedative.
EEG's assist physicians in the diagnosis of a variety of neurological
problems, from common headaches and dizziness to seizure disorders,
strokes, and degenerative brain disease. The EEG is also used to
look for organic causes of psychiatric symptoms and disabilities in
children, and can assist physicians in determining irreversible brain
death.
Ambulatory EEG
Ambulatory EEG is done to study seizure activity which is difficult to
record during normal EEG. The electrodes are placed o head and secured
with a special procedure. A portable unit records EEG activity
continuously for 24 hours.
Non-Invasive
Carotid (NICS) Study
NICS is an ultrasound that provides a method by which anatomy can be
imaged and blood flow detected and measured for diagnostic
purposes. This is accomplished by sending ultrasound into the
tissues and receiving the echoes returning from the tissues, a two
dimensional cross-sectional image and blood flow displays. It is
most commonly done to study blood flow to brain in stroke.
Transcrannial
Doppler (TCD) Study
TCD is an ultrasound that provides a method by which intracranial flow
velocity and flow direction measurements can be sampled. It is most
commonly done to study blood supply to brainstem and back part of brain.
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