You can have a normal electromyography (EMG) test result and have amyotrophic lateral sclerosis (ALS). It depends on the stage of your ALS and the type of ALS you have.

Most of the time, the results of an EMG will be abnormal in individuals with ALS because the test measures specific aspects of nerve and muscle function. ALS affects your voluntary muscle movements, making things like walking, talking, and swallowing progressively difficult.

EMG is an electrical test that examines the muscle activity, usually in the limbs. During this test, a needle is inserted into the muscle, and the muscle’s reaction to stimulation is assessed. ALS causes degeneration of nerves in the lateral (side) region of the spinal cord that stimulate voluntary muscles.

The lack of nerve stimulation makes the muscles weak, and eventually, the muscles atrophy (shrink). In addition to weakness, spontaneous muscle twitches are a specific feature of ALS.

The muscle weakness is seen in EMG testing. The EMG result pattern consistent with weakness is not necessarily unexpected in the context of the symptoms and is not specific to ALS. There are also certain EMG patterns that are more specific to ALS – something called fibrillation, which are spontaneous electrical signals detected with EMG that correlate with the muscle twitches.

ALS doesn’t affect muscles in a symmetrical or equal fashion on both sides of your body, especially in the early stages, and that’s why an EMG test might be normal even if you have ALS.

It’s rare, but sometimes if you are in the very early stages of ALS, you will not have muscle weakness or other measurable symptoms yet.

For example, if you have a type of ALS called Bulbar-onset ALS, it affects the face and mouth before affecting the arms and legs. This is another reason an EMG test may be normal.

Having a normal EMG may mean you do not have ALS, but there’s no single test that diagnoses or rules out ALS. Diagnosing ALS involves several tests and exams, including:

While rare, you may have a normal EMG test and have ALS. It can happen if you are in the very early stage of the disease.

If you are being tested to see if you have ALS, talk with your doctor or healthcare team about any questions or concerns you have. They can explain what tests you are having, why you need them, and what the results mean.