Related To Category: Adult
Nerve conduction study (NCS)
Nerve conduction studies are preformed first. The goal of the test is to study your nerves. This is done by taping small metal disks to the skin over the nerve area to be tested. A small electrical current is then used to stimulate the nerve. This process will be repeated over several areas and may also be done at different sites along the nerve. It should be noted that the electrical current produces a tingling sensation that may be slightly uncomfortable to some.
Nerve conduction studies are used mainly for evaluation of paresthesias (numbness, tingling, burning) and/or weakness of the arms and legs. The type of study required is dependent in part by the symptoms presented. A physical exam and thorough history also help to direct the investigation. Some of the common disorders which can be diagnosed by nerve conduction studies are:
The nerve conduction study consists of the following components:
The second part of the test is an EMG designed to study your muscles. First, a small metal disc (about the size of a fifty-cent piece) will be taped to your skin. The EMG doctor will then insert a small needle into your muscle in order to record your muscle’s electrical activity. EMG testing may be done on several different muscles (but each muscle will be tested on its own). During the test, you will hear a crackling speaker sound. This is the electrical activity from your muscles, changed into sound waves. You do not receive any electrical stimulation for this part of the test. The EMG can be somewhat uncomfortable because of the needle used. For a day or two after the test, you may feel some tenderness or notice a small bruise around the sites where the needle was inserted.
EMG/NCS Can Help Diagnose:
Carpal Tunnel Syndrome
Arm or Leg Numbness/Pain
Amyotrophic Lateral Sclerosis (ALS) or
Lou Gehrig’s Disease
When are NCSs/EMGs used?
A doctor may recommend that you undergo this test. There are a wide variety of conditions that are assessed with this technique. Quite frequently, the examination is requested because the patient is experiencing symptoms that suggest some problem with the nerves (numbness, tingling, weakness or pain) or muscles (weakness or pain), even though the physical examination is normal. Indeed, in many cases, there is no abnormality seen and the test can then be reassuring, but it cannot detect all conditions. In general terms, the test is useful for detecting if there is a significant abnormality, but this is also often easier when there is a definite clinical abnormality. In such cases, the test can help clarify what the problem is, although usually, unless the nerve problem is a common entrapment (site of compression), other tests may be required to ascertain the exact nature of the problem.
What does an NCS/EMG detect?
There are several types of nerves but generally speaking, the two major types aremotor and sensory nerves. Motor nerves carry signals from the brain to the muscle to enable contraction and movement, and sensory nerves relay information to the brain. When the nerve is stimulated with metal electrodes (metallic patch/es that can conduct signals), a response can be measured by surface (on the skin) electrodes some distance away in sensory nerves overlying the nerve itself. For the motor nerves, the response is usually detected over the muscle that is activated by that nerve. In this fashion, results can reveal information about the size and speed of the electrically conducted impulse. The size usually reveals the number of nerve fibres present and the speed, the integrity of the myelin (insulating membrane around the nerve ‘axon’ or cable). This is why the word ‘conduction’ is used.
This can pick up electrical signals in the muscle either in its resting state or with activation of the muscle. As mentioned earlier, it is useful for looking at both the nerve and the muscle but this portion of the test, being invasive, is not always employed.
Preparing for an NCS/EMG
You will be given instructions on how to prepare for the test. You should not use creams or emollients on your hands and feet (the most common sites of your nerve tests) on the day of the test, and preferably since your last shower or bath. Generally speaking, there are no other preparations of note.
Please advise the neurologist performing the test if you have a pacemaker or other similar devices. If you are taking warfarin, heparin or some other medication to thin your blood, and if you are having a needle EMG test, you should advise both your GP and the neurologist. A measurement of how thin your blood is may be important before that test can be performed.
The NCS procedure is usually very safe and is non-invasive. Firstly, you will be told how to position yourself and the skin area will be prepared. Then some electrodes will be attached to your skin and you will be forewarned when to expect the stimulation. Many people are understandably anxious about the intensities of the small safe electrical pulses that are passed via the skin, but usually relax quickly when they know what to expect. It is faily important that you remain relaxed for the recordings to minimise the ‘noise’ (interference) in the recordings from excessive muscular activity.
Here, a small needle is inserted through the skin into a muscle belly. Sterilisation of the skin and a local anaesthetic is not generally required. Usually the consultation and procedure takes about 30-45 minutes in all. More complicated assessments may demand more time.
What happens after an NSC/EMG?
Following the test, you will be allowed to put on your garments and shoes. It should be noted that the final interpretation of the clinical meaning of the test rests with the clinician who ordered the test. This is because they can put together the whole picture. For this reason, the neurologist performing the test can only give you limited information about the meaning of the results, and may not even be able to provide any information on the next step or any possible treatments because they are unaware of all the other clinical information.