An electromyography (EMG) test is a diagnostic procedure utilized to assess the health of muscles and the nerve cells that control them. These nerve cells, known as motor neurons, transmit electrical signals that cause muscles to contract. An EMG translates these electrical signals into graphs, sounds, or numerical values, aiding in the diagnosis of conditions affecting muscles, nerves, or the junction where nerves meet muscles, which can manifest as weakness, tingling, or numbness.
Preparing for the Test
Before an EMG test, patients often receive specific instructions to ensure accurate results. It is important to discuss all medications, especially blood thinners, with the healthcare provider beforehand, as some may need temporary adjustment. Patients are advised to avoid applying lotions, creams, or oils to their skin on the day of the test, as these substances can interfere with the electrical readings. Wearing loose-fitting clothing is also recommended to allow easy access to the areas that will be tested.
Patients should inform the technician if they have a pacemaker, implanted defibrillator, or any other implanted medical devices. These devices might require special precautions during the test. The healthcare provider administering the test will provide precise instructions tailored to the individual’s situation. Following these instructions carefully helps ensure a smooth and effective diagnostic procedure.
The Nerve Conduction Study
The nerve conduction study (NCS) is the first part of an EMG examination, measuring how quickly and well the body’s electrical signals travel along nerves. During this procedure, surface electrodes are placed on the skin over specific nerves and muscles. A mild, brief electrical impulse is then delivered through a stimulating electrode placed at one point along the nerve. This impulse causes a brief, mild tingling sensation or a muscle twitch.
Another recording electrode, positioned further down the nerve or over the muscle it supplies, detects the electrical activity generated by this stimulation. The technician measures the time it takes for the electrical signal to travel from the stimulating electrode to the recording electrode. This measurement helps determine the nerve conduction velocity. The strength of the nerve’s signal, or amplitude, is also recorded. Multiple nerves in different areas of the body may be tested to provide a comprehensive assessment of nerve function.
The Needle Examination
Following the nerve conduction study, a needle examination is performed, which directly assesses the electrical activity of muscles. For this part of the test, a thin, sterile needle electrode is inserted into various muscles. This needle is not used to inject any substances but rather acts as a recording device. The healthcare professional will move the needle slightly within the muscle to assess electrical activity in different areas.
The electrical signals are observed on a monitor and can also be heard through a speaker. The muscle’s electrical activity is first recorded while it is at rest. Normally, healthy muscles show no electrical activity at rest.
The patient is then asked to slightly contract the muscle. This allows the doctor to observe the patterns of electrical activity during voluntary muscle contraction. The process may cause a sensation of muscle soreness or pressure, but it is well-tolerated.
After the Test
After an EMG test, patients can resume normal activities without significant restrictions. Some individuals may experience minor muscle soreness, tenderness, or slight bruising at the sites where the needle electrodes were inserted. Applying an ice pack to these areas can help alleviate any discomfort. These mild after-effects subside within a day or two.
The findings from both the nerve conduction study and the needle examination are then analyzed by a healthcare professional, often a neurologist. This specialist interprets the electrical patterns and measurements to determine if there are any abnormalities in nerve or muscle function. The results are communicated to the patient either during a follow-up appointment or through a phone call. This allows for a detailed discussion of the findings and any next steps for diagnosis or treatment.