Diagnostics
Electromyography (EMG)
Electromyography (EMG) is a diagnostic test that measures the electrical activity of muscles and the nerves controlling them. This test helps detect issues with motor nerves, muscles, or the connection between them.
Other names for the test are electrodiagnostic study, EMG test, or electromyogram.
Who conducts EMG?
Neurologists often combine an EMG with a nerve conduction study (NCS) to assess nerve function. The NCS measures the electrical current flowing through a nerve before it reaches a muscle, while the EMG measures how muscles respond to electrical activity.
The test can be done in an outpatient setting or during a hospital stay, depending on the specific situation.
Why is EMG performed?
The doctors may recommend an EMG if the patient experiences symptoms like muscle weakness, numbness, or tingling.
EMG results are vital in diagnosing or ruling out various conditions, including:
- Muscle disorders like muscular dystrophy or polymyositis.
- Diseases that impact the connection between nerves and muscles, such as myasthenia gravis.
- Disorders affecting peripheral nerves outside the spinal cord, like carpal tunnel syndrome or peripheral neuropathies.
- Conditions that affect motor neurons in the brain or spinal cord, such as amyotrophic lateral sclerosis or polio.
- Disorders that affect nerve roots, such as a herniated disc in the spine.
How is EMG conducted?
Before the EMG procedure
- Take a bath or shower and wear comfortable, loose-fitting clothing.
- Avoid applying cream, lotion, or perfume on the skin, as it can affect the accuracy of the test.
- The patient should inform the doctor if they are taking blood thinners such as warfarin. These medications may increase the risk of bleeding after the test. However, do not stop taking medication without consulting a doctor who prescribed the medication.
- Inform the doctor if there is a pacemaker or any other electrical medical device in place.
- Adhere to any specific instructions provided by the doctor, which may include avoiding smoking cigarettes or consuming caffeinated beverages like coffee or tea for a period of two to three hours before the test, as these substances can potentially disrupt the test results.
During the EMG procedure
- The patient will be positioned sitting or lying on a table or bed.
- The technician will clean the skin over the muscle that will be tested.
- A needle electrode with a mild electric current will be inserted into the muscle. The patient may feel slight pain or discomfort during this process.
- The machine will record the muscle activity while the muscle is at rest.
- The patient will be instructed to slowly and steadily contract the muscle. The machine will record this activity as well.
- The electrode may be repositioned to record activity in different muscles.
- The electrical activity will be displayed as wavy and spiky lines on a video screen. It may also be recorded and played through an audio speaker.
The EMG test can last for 60 to 90 minutes, depending on the number of muscles tested. After the test, the patient may experience muscle soreness or tenderness, usually mild and improving within a week. Observing some bruising at the needle insertion sites on the skin is also possible. However, this is temporary and should fade over time.
The patient will receive the results of the EMG test within 24 to 48 hours after the completion of the testing. The neurologist will analyze the results and generate a report. The doctor who recommended the EMG test will discuss the report with the patient during a follow-up appointment.
References
- Electromyography (EMG) and Nerve Conduction Studies. Available from: https://medlineplus.gov/lab-tests/electromyography-emg-and-nerve-conduction-studies
- Cleveland Clinic. EMG (electromyography). Available from: https://my.clevelandclinic.org/health/diagnostics/4825-emg-electromyography
- Electromyography (EMG). Available from: https://www.mayoclinic.org/tests-procedures/emg/about/pac-20393913#:~:text=Electromyography%20(EMG)%20is%20a%20diagnostic,%2Dto%2Dmuscle%20signal%20transmission
