What is Electromyography (EMG)?
Muscles need electric signals in order to contract and produce movement. Electromyography (also called EMG) is a diagnostic procedure done to evaluate the health of muscles which are under voluntary control (skeletal muscles) and record its electrical activity based on how nerves control them.
Electromyography uses a electromyograph, a machine that allows the physician to see a graphical form of electrical signals to observe and interpret trends of electricity generated by the muscles in response to stimulation and movement.
Why is EMG Performed?
A EMG is prescribed usually when patients experience muscle weakness, muscle pain, cramps, tingling sensation, numbness and all other symptoms related to muscular discomfort. EMG will help physicians get a definite diagnosis and rule out other disease conditions.
The following conditions are common indications for EMG:
- To establish presence of muscle disorders (e.g muscular dystrophy or polymyositis)
- To identify diseases which affects connection between the nerve and the muscle (e.g. myasthenia gravis)
- To establish presence of nerve disorders outside the spinal cord (peripheral nerves), such as carpal tunnel syndrome or peripheral neuropathies
- To establish and diagnose disorders affecting neurons inside the brain and spinal cord that are mainly responsible for bodily movement (e.g. amyotrophic lateral sclerosis or poliomyelitis)
- To identify nerve root disorders (e.g. herniated disk of the spine)
Types of EMG Tests
There are several types of EMGs which may vary, depending on the purpose of the procedure.
- Needle EMG (Intramuscular EMG): Needle EMG is performed by inserting a small, thin disposable needle through a group of muscles that are suspected to cause discomfort. As the needle is inserted, the patient might feel a small amount of pain. The needle will pick up electric signals generated by the muscles, and then send it to the EMG machine so that the doctor could observe its trend.
- Nerve Conduction Studies: Nerve conduction studies help to understand how effective the flow of electricity through nerves. The physician applies a small amount mild, tingling electrical shock to the nerve. Nerve conduction tests could be helpful in diagnosing carpal tunnel syndrome, Guillain-Barre syndrome and spinal disc herniation.
- Evoked potentials: Also known as ‘evoked response’, Evoked potentials is a method of EMG testing which checks the nerve pathways and evaluate the amount of time it takes for nerves to respond to stimulation. This test works by stimulating senses such as vision (Visual-evoked response), hearing (auditory brainstem evoked response), or by stimulating the arms and the legs through electrical pulse (somatosensory evoked response).
What are the Diseases/Conditions EMG is typically indicated for?
EMGs are commonly performed to aid in the diagnosis of these diseases:
- Carpal tunnel syndrome
- Cubital Tunnel Syndrome
- Guillain-Barre syndrome
- Guyon’s canal syndrome
- Peripheral neuropathy
- Peroneal neuropathy
- Spinal disc herniation
- Tarsal Tunnel Syndrome
- Ulnar neuropathy
- Neuromuscular Junction Disorders
- Multiple Sclerosis
- Myasthenia Gravis
How is EMG performed?
Before the procedure, you will be asked to wear loose clothing to allow easy access to site where electrodes/needles will be placed. You should also refrain from applying lotions and oils to the skin. People with pacemaker, a medical implant which keeps the heart beat in the proper rhythm, should inform the operator before EMG is done.
During the procedure, you will be asked to remove all jewelries, hair accessories and all other metal objects. The patient may be asked to lie down or to sit during the test. An antiseptic solution will be used to clean the skin before the sterile disposable needle is inserted to the muscle. There will be slight pain as the needle is inserted but in In general, EMGa are a painless procedure.
For nerve conduction tests, a special lubricant may be applied to the skin before patches of electrodes are attached. You may feel brief period of shock as small amount of electricity flows through the electrode.
What to expect after the procedure? Are there any risks?
Muscle soreness may be felt in the site of injection after the procedure. If you notice bleeding, or pain that is increasing, accompanied by swelling and pus in the injection site, notify your physician.