Electromyography (EMG) for ALS diagnosis

Electromyography (EMG) is a needle test that records electrical activity in muscles both during contraction and at rest. The test can detect lower motor neuron dysfunction seen in amyotrophic lateral sclerosis (ALS). Doctors usually use EMG for ALS along with other tests, such as nerve conduction studies, to support an ALS diagnosis.

Why is EMG used for ALS?

EMG for ALS helps doctors assess the health of muscles and motor neurons.

Motor neurons are nerve cells that use electrical signals to help control voluntary muscle movements. Upper motor neurons travel from the brain to the spinal cord, while lower motor neurons travel from the spinal cord to muscles throughout the body.

In people with ALS, motor neurons die, leading to muscle weakness, cramps, or persistent twitching. An EMG can detect changes in electrical activity that may indicate motor neuron dysfunction.

If ALS is suspected, a doctor may use an EMG to help make a diagnosis.

Can an EMG diagnose ALS?

No single test can diagnose ALS. Doctors reach a diagnosis by reviewing a person’s medical history, performing a neurological exam, and ordering tests to rule out other conditions that mimic ALS.

EMG is one component of this evaluation. Other tests used during diagnosis include:

• nerve conduction studies
• blood and urine tests
• MRI
• spinal tap
• muscle or nerve biopsy

How should someone prepare for an EMG?

Before an appointment, a person should consult their physician about preparation, and follow these general guidelines:

What happens during an EMG appointment?

A neurologist or lab technician typically performs an EMG on an outpatient basis. An EMG and nerve conduction study usually happen consecutively, with the nerve conduction study occurring first.

Nerve conduction studies

A nerve conduction study measures how fast and how strongly an electrical signal travels along a nerve before reaching a muscle.

During a nerve conduction study, the process usually follows these steps:

1. The patient removes clothing, jewelry, hearing aids, or metal objects that might interfere with signals.
2. The patient sits or lies down comfortably.
3. The healthcare professional places stimulating electrodes and recording electrodes over the targeted nerves.
4. The stimulating electrode sends a brief electrical pulse to activate the nerve, while the recording electrode measures signal strength and speed.
5. The electrodes are removed.

Needle EMG

The neurologist typically performs the needle EMG immediately after the nerve conduction study.

During the needle EMG, the process typically proceeds as follows:

1. The neurologist selects specific muscles and cleans the skin with an antiseptic wipe.
2. The neurologist inserts thin needle electrodes into the muscles.
3. The patient relaxes, then moves the muscle in specific ways, such as lifting or flexing a limb.
4. A device connected to the needles records the muscle’s electrical activity at rest and during contraction.
5. After examining one muscle for a minute or two, the neurologist moves to the next muscle.
6. The neurologist removes the needles.

Why several muscles may be tested

During an EMG for ALS, clinicians commonly test muscles in different areas of the body, even if the patient feels no weakness in those specific spots. This evaluation often includes regions commonly affected in ALS, such as the lower back, torso, arms, neck, and muscles involved in swallowing and speaking.

The test generally takes from 60 to 90 minutes, depending on how many muscles are tested.

Does an EMG hurt?

The person receiving an EMG may feel some slight pain or discomfort when the needles are inserted. Patients should report any pain during testing, as discomfort may affect the results.

After the test, a person’s muscles may feel sore or tender for a couple of days. Complications are rare, but any increasing pain, tenderness, swelling, or pus at the needle site should be reported to their doctor right away.

What does an ALS EMG show?

An ALS EMG test can detect signs of lower motor neuron dysfunction, sometimes before symptoms appear on a physical exam. The test also reveals changes that occur when surviving motor neurons form new connections with muscles that have lost their normal nerve supply. These may be signs of ALS.

EMG abnormalities that suggest ALS include:

• abnormal electrical signals that can indicate muscles are losing their nerve supply
• spontaneous electrical discharges associated with muscle twitching
• changes in motor unit activity, which can reflect the loss of motor neurons

An abnormal EMG alone cannot diagnose ALS, and a normal EMG does not completely rule out ALS, especially early in the disease. EMG results must be considered alongside:

• symptom assessment
• a neurological exam
• the results of other tests

What are the risks of an EMG?

EMG carries minimal risk. The needles are very thin, so most people experience only minor discomfort and slight bruising.

Because there is a small risk of bleeding, patients should inform their healthcare team if they have hemophilia or take blood-thinning medications. Furthermore, the electrode detects electrical signals rather than producing them, so patients do not experience electrical shocks during the test.

Questions to ask before and after an EMG

If a doctor recommends an EMG test, consider asking these questions:

• Why are you recommending an EMG, and what are you looking for?
• Will I also have a nerve conduction study during the same appointment?
• How should I prepare for the EMG, and are there medications I should avoid beforehand?
• What will the EMG feel like, and how long will the test take?
• Which muscles will you test, and why did you choose those muscles?
• What did my EMG results show about my muscles and motor neurons?
• Did the results show signs of lower motor neuron damage that could be associated with ALS?
• Could anything besides ALS explain these findings?
• What other tests or evaluations do I need to determine the cause of my symptoms?
• What are the next steps based on my EMG results?