Electromyography (EMG) Laboratory

• Jun Kimura, MD (Director)
• Edward Aul, MD (Co-Director)
• James Worrell, MD

Fellows:

• Robert Gilbert, MD

Technologists:

• Sheila Mennen, RNCST (Chief Technologist)
• Leigha Rios, RNCST, REEGT
• Wendy Sebetka, RNCST, REEGT

Services:

• Nerve Conduction Studies (NCS)
• Electromyography (EMG)
• Repetitive Nerve Stimulation (RNS)
• Intra-Operative Monitoring (IOM)

Additional Information:

• The EMG: Electromyography Test

I. Background

The EMG Laboratory of the University of Iowa Heath Care system performs a variety of electrodiagnostic studies, including nerve conduction, electromyography and special procedures, such as repetitive nerve stimulation and intraoperative monitoring. These techniques are used as an adjunct to the clinical neurologic examination and are valuable in the evaluation of disorders of peripheral nerve and muscle, i.e. neuromuscular diseases. These studies can be performed to assess individuals with muscular weakness, numbness, tingling, pain or loss of balance, either to confirm or establish the diagnosis of neuromuscular disease. Conditions regularly encountered in the University of Iowa Heath Care EMG Laboratory include: carpal tunnel syndrome and other compressive or traumatic nerve injuries; degenerative, inflammatory, or hereditary disorders of nerve (neuropathy) or muscle (myopathy); spinal nerve injuries; and less common disorders, such as myasthenia gravis and amyotrophic lateral sclerosis (Lou Gehrig’s Disease). In addition to aiding diagnosis, these tests can help determine prognosis and guide therapy.

II. Nerve Conduction Studies (NCS)

Nerve conduction studies are used to evaluate the function of peripheral nerves. Brief, low intensity electric shocks are applied to individual nerves with a stimulating electrode, and electrical responses are measured from recording electrodes placed on the skin surface over another site on that nerve or over a muscle supplied by the nerve. Response size (amplitude) and delay (latency) are recorded. Nerve conduction velocities are calculated. The number and location of nerves examined is dictated by the clinical history and examination. The pattern of abnormalities helps localize and define disorders of peripheral nerve.

III. Electromyography (EMG)

Electromyography is used to assess muscle. A thin needle electrode is inserted into muscle to record electrical activity while the muscle is at rest and with muscle contraction. No electric shocks are applied, though there is some degree of pain associated with needle placement. The distribution and type of recorded abnormalities helps to differentiate disorders of nerve and muscle and provides important information regarding pathology or the basis of these disorders. Most needle electrodes are disposable and are discarded after each study. Non-disposable needles are sterilized before each use.

IV. Repetitive Nerve Stimulation (RNS)

Repetitive nerve stimulation tests are a special type of nerve conduction study. Rather than a single electric shock, a brief series of shocks is applied to a motor nerve and responses are recorded from a muscle supplied by that nerve. The study is generally performed before and after brief exercise of the muscle. Serial response amplitudes are recorded. Repetitive nerve stimulation is useful for evaluating myasthenia gravis and other disorders of neuromuscular transmission.

V. Intra-Operative Monitoring (IOM)

The same techniques used to evaluate patients in the EMG laboratory can be used in the operating room. Intraoperative monitoring facilitates the differentiation of neurologic from non-neurologic structures in the surgical field, the identification of specific nerves or nerve roots, and the prevention of nerve injuries. These studies are frequently performed during surgeries of the spine, peripheral nerves or areas adjacent to vital nerve structures.

VI. Preparing for Studies

Routine studies usually consist of some combination of nerve conduction studies and electromyography, depending on the patient’s symptoms and the request of the ordering health care provider. Patients may participate in normal activities before and after they are done. Although there may be some discomfort during shock or needle insertion, there are no lasting side effects. Patients should bathe or shower before the procedure to remove excess skin oil. Body lotion should not be used prior to examination. Because needle electrodes are used during electromyography, it is imperative that patients inform the testing physician if they are taking blood thinners or have a disorder of blood coagulation. Testing physicians should also be informed of cardiac pacemakers, medication pumps, or other electrical devices, which may produce recordable signals during evaluation. Some medications may interfere with accurate study interpretation. Patients should check with their health care providers to determine whether any medications should be temporarily discontinued for the procedure. The studies usually take 30 to 90 minutes. Results are available immediately after completion.