What is Electromyography (EMG)?
Electromyography (EMG) is an electro diagnostic medicine technique used to evaluate the electrical activity produced by skeletal muscles. This is done by using an instrument known as electromyograph that produces a record called as electromyogram.
Electromyogram records the electrical potential generated by muscle cells once they are electrically or neurologically activated.
EMG may be ordered by a doctor if there are any signs or symptoms of nerve or muscle disorder. The symptoms may include:
- Muscle weakness
- Muscle pain or cramping
- Pain in limbs
There are number of other conditions where EMG results may be useful:
- Muscle disorders: e.g., muscular dystrophy or poliomyositis (inflammation of many muscles)
- Myasthenia gravis is the commonest disorder of neuromuscular contraction/
- Peripheral nerves disorders: e.g. carpal tunnel syndrome (numbness and tingling in the hand), peripheral neuropathies.
- Amyotrophic lateral sclerosis or Lou Gehring’s disease
- Herniated disk in the spine, where nerve root is affected
While EMG is being conducted, a related test known as nerve conduction study (NCS) may be performed. NCS is done before an EMG if both tests are being conducted and can take from 15 min to 1 hour, depending on how many nerves and muscles are being studied. NCS is used to determine the amount and speed of conduction of electrical impulse through a nerve. Further, it also helps to estimate damage and destruction to the nerve. Both these procedures assist in determining the presence, location and extent of disease that damages the nerve and muscles. Care must be taken to keep the body temperature normal during the NCS test, as low body temperatures slow down the nerve conduction.
Though EMG is a low-risk procedure and without known complications, there could be:
- Small risk of bleeding, infection and nerve injury when an electrode needle is inserted.
- Leakage of air into the area between lungs and chest wall, thereby causing collapse of lung (pneumothorax), when muscles along the chest walls are examined with needle electrode.
- Patients with gross edema and taut skin can have leakage of serous fluid, when their skin is punctured by needle electrodes. This oozing of serous fluid may result in cellulitis. Hence prior risks need to be weighed by the physician.
- No known cases of cellulitis, infection or other risks have been reported in patients with lymphedema. But, still caution has to be observed in doing needle examinations in lymphedematous regions so as to avoid complications.
- In pregnant patients, no known complications have been reported.
Before the procedure
Your doctor (usually a neurologist) will explain to you about the process and give an opportunity to you for asking questions. Generally, there is no need for fasting before the test and in some cases, cigarettes and caffeinated beverages like, tea, coffee and cola have to be restricted for 2-3hours before the test.
- Notify your doctor about the following if:
- Taking any medications and herbal supplements
- Any pacemaker or any other electrical device has been inserted
- Using any blood-thinning medications
- Suffering from hemophilia
- You may be asked:
- To dress in clothes that permit access to the areas to be tested and which are easily removable.
- Avoid using lotions or oils on your skin for a few days before the procedure or refrain from using during the day of testing.
- Taking a bath before the procedure in order to remove oil from your skin.
During the procedure
EMG procedure is done on an outpatient basis or as an inpatient procedure.. The procedure may vary depending on your condition and your doctor’s practices. This process is immediately done after nerve conduction study.
- You will be given a gown to wear and will be asked to remove clothing, jewelry, hairpins, hearing aids, any metallic objects, eyeglasses or any other objects that may interfere with the process.
- You will be made to sit or lie down for the test and your doctor (neurologist) will locate the muscle that needs to be studied.
- The skin would be cleansed with an antiseptic solution and sterile needle will be inserted into the muscle. A ground electrode would then be kept under your arm or leg.
- Usually more than 5 needle insertions may be necessary for the test and therefore you may experience slight pain, but it’s otherwise painless. In case if you feel pain, you must inform your examiner as this may interfere with the test result.
- Relaxation may be needed during the test and you will also be required to do slight or full-strength muscle contractions.
- Electrical impulses from your working muscle will be measured and shown on the oscilloscope.
- During the whole process, an audio amplifier may also be used for evaluating appearance and sound of electrical potentials. Sound of muscle contraction can be heard if recorder is connected to an audio amplifier.
After the procedure
- Electrodes will be removed from the skin and also any paste attached to it.
- You can resume your normal activities, unless differently advised by doctor. Also, additional information may be given after the procedure, but this varies as per individual’s situation.
- There may be slight bruising where the needle electrodes are inserted, which will fade out eventually. If it persists, contact your doctor.
- Clothing: You will be asked to wear a hospital gown for the procedure and lie on examination table.
- Electrodes: Various surface electrodes may be placed at several locations of your skin depending on where the symptoms are experienced, or needle electrodes may be inserted at different sites depending on the symptoms.
- Consciousness: Electrodes inserted or placed will transmit minute electrical current that can give a feeling of twinge or spasm. Pain can also be experienced from needle electrodes on their removal. Any concerns related to pain should be discussed with your neurologist and if possible short break can be taken during the procedure.
- Directions: Any kind of electrical activity in your resting muscle during the needle EMG procedure will be assessed by your neurologist. You will be provided with a specific set of directions for resting and contracting a muscle at appropriate times. Depending on the type of muscles that is being examined, your doctor would ask you to alter your positions during the procedure.
- Physical therapy, particularly stretching is essential in maintaining motion for affected muscles.
- Strengthening other muscles can also compensate for weakness in affected muscles, especially in earlier stages.
- Exercising regularly is necessary for overall maintenance of good health, but strenuous exercise should be avoided as it can lead to muscle damage.
- Electromyography - (https://en.wikipedia.org/wiki/Electromyography)
- Electromyography (EMG) - (http://www.hopkinsmedicine.org/healthlibrary/test_procedures/neurological/electromyography_emg_92,p07656/)
- Diseases & Conditions - (http://my.clevelandclinic.org/health/diseases_conditions/hic_muscular_dystrophy)
Latest Publications and Research on Electromyography (EMG)
- [The diagnostic value of tremor analysis for defining the Parkinson's disease subtype]. - Published by PubMed
- Effect of seat tube angle and crank arm length on metabolic and neuromuscular responses and lower extremity joint kinematics during pedaling with a relatively lower seat height. - Published by PubMed
- Intraoperative nociception-antinociception monitors: A review from the veterinary perspective. - Published by PubMed
- Surface electromyography - A diagnostic and monitoring biomarker for amyotrophic lateral sclerosis? - Published by PubMed
- [Effect of neuromuscular blockade on the bispectral index in critically ill patients]. - Published by PubMed