An electromyography (EMG) is one of the key tests in diagnosing amyotrophic lateral sclerosis (ALS). It is also referred to as “needle EMG” and is normally performed alongside nerve conduction studies.
Muscle movement is controlled by electrical signals passed from motor neurons (a type of nerve cell). In most cases of ALS, these neurons no longer work correctly, leading to a decrease in the patient’s ability to use certain muscles. An EMG is used to assess the health of the muscles and the motor neurons that control them.
What happens during the test?
During an EMG, a small needle electrode (a device to deliver or detect electrical signals) is inserted into the muscle. The electrode is connected to a device which records the electrical activity of the muscle at rest and when it contracts.
The patient is asked to move in a certain way to test how the muscles react. When diagnosing ALS, it is common for muscles in different areas of the body to be tested regardless of whether the patient has experienced symptoms such as muscle weakness in that area. This can include muscle regions commonly affected in ALS such as the lower back, torso, arms, and neck, as well as muscles associated with eating, swallowing, and speaking.
The procedure generally takes from 30-60 minutes.
What do the results mean?
Patients with ALS tend to show abnormal EMG results, especially if there are significant signs of lower motor neuron (LMN, in the spinal cord) involvement. The test can identify the onset of LMN involvement before symptoms are obvious. A common abnormal result in ALS patients is spontaneous electrical activity when the muscle is at rest. A normal EMG result will often result in a diagnosis of primary lateral sclerosis (PLS), but does not rule out the possibility of ALS developing later.
Risks associated with the test
There is very little risk associated with an EMG, although patients should inform EMG personnel if they have a pacemaker, hemophilia, or are taking blood-thinning medications. Patients who have had an EMG generally do not report any pain. The needle is very fine, so the patient generally only experiences minor discomfort and slight bruising in the affected area. During the EMG, the electrode is used only to detect electrical signals so the patients do not experience any electrical shocks.
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