Electromyography (EMG) is a specialized diagnostic tool used to assess the health of both muscles and the motor nerves that control them. The procedure is typically ordered when a patient experiences symptoms like muscle weakness, persistent tingling, or unexplained numbness. Concern about discomfort is the most common apprehension people have regarding this test, largely due to the use of electrical stimulation and fine needles. Understanding the process can significantly reduce this anxiety, providing a clear expectation of the sensations involved.
What is an EMG and Why is it Performed?
An EMG is a form of electrodiagnostic testing that measures the electrical activity within muscles and nerves. The EMG procedure helps physicians determine if a patient’s symptoms are caused by a problem with the nerve itself, the muscle tissue, or the communication point between the two, known as the neuromuscular junction. Physicians use the test to diagnose or rule out a wide range of neuromuscular conditions.
These include nerve entrapment syndromes, such as carpal tunnel syndrome, or conditions affecting the peripheral nerves, like peripheral neuropathy. It is also valuable in identifying muscle diseases, such as muscular dystrophy, and disorders that affect nerve roots, like a herniated disk causing nerve root compression. By translating the electrical signals into graphs, sounds, and numerical values, the test provides objective data on the functional integrity of the body’s motor system.
The Two Components and the Sensations Felt
The comprehensive EMG test is typically performed in two distinct stages, each involving different equipment and unique physical sensations. While the overall procedure may cause discomfort, it is generally well-tolerated by most patients. The goal of the procedure is to gather accurate data, which requires the patient to remain as relaxed as possible.
Nerve Conduction Study (NCS)
The Nerve Conduction Study (NCS) assesses the speed and strength of electrical signals traveling along nerve pathways. During this part, surface electrodes, which are essentially stickers, are placed on the skin at various points along the nerve being tested. The technician then delivers a very small, brief electrical impulse to stimulate the nerve.
The sensation during the NCS is often described as a sudden, brief “tingle,” “zap,” or a feeling similar to a mild static electricity shock. This feeling is momentary, lasting only as long as the stimulation is applied, and it may cause the muscle it controls to twitch involuntarily. The intensity of the electrical impulse is controlled by the technician to ensure the nerve is adequately stimulated for measurement.
Needle Examination (Needle EMG)
The Needle Examination focuses on the muscle’s electrical activity directly. For this part, the physician inserts a very fine, sterile needle electrode through the skin and into the specific muscle being examined. The needle itself is a recording device, similar to a microphone, and no electrical stimulation is delivered through it.
When the needle is initially inserted, patients typically feel a brief, sharp prick, followed by a sensation of deep pressure or a dull ache as the needle is moved. The physician first records the muscle’s electrical activity while it is completely at rest, then asks the patient to contract the muscle slightly. Contracting the muscle with the needle inside may produce a cramping or heavy sensation, but the discomfort is typically minor and short in duration for each site.
Preparation, Duration, and Recovery
Preparation for the test helps ensure accurate results and minimizes discomfort. Patients should avoid applying any lotions, oils, or creams to their skin on the day of the test, as these substances can interfere with the adherence and function of the surface electrodes. It is also helpful to wear loose, comfortable clothing that allows easy access to the limbs being tested.
Patients should inform the physician beforehand about any medications they are taking, especially blood thinners, or if they have an implanted electronic device, such as a pacemaker. The entire electrodiagnostic study, including both the NCS and the Needle EMG, generally takes between 30 and 90 minutes. Following the procedure, there is typically no significant recovery period, and most people can immediately resume their normal daily activities. Mild muscle soreness, tenderness, or minor bruising at the needle sites is common but usually resolves within one to two days.