How Amyotrophic Lateral Sclerosis (ALS) Is Diagnosed

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Diagnosing amyotrophic lateral sclerosis (ALS) is not straightforward. There is no single test to confirm ALS. A healthcare provider, such as a neurologist, will take a full medical history, conduct a physical exam, and order more specific muscle and imaging tests.

This article discusses the different tests and procedures used to diagnose ALS, as well as symptoms and other diseases that may be mistaken for ALS.

Man in a wheelchair

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ALS is a progressive disease that causes the nerve cells in the brain and spinal cord that send messages to the muscles of the body to deteriorate. It affects basic voluntary movements, such as walking, talking, and chewing.

Over time, the brain can no longer initiate or control movement. The muscles of the body atrophy, or waste away, causing more severe symptoms.

Self-Checks/At-Home Testing

There is no way to test for ALS at home. However, knowing the symptoms can help you recognize when you should to talk to a healthcare provider. Understanding the signs of ALS and knowing how they affect your body can help you communicate any changes you notice in your body’s function.

Early ALS symptoms are usually subtle, but eventually become more noticeable as the muscles weaken.

Some signs to look for in the early presentation of ALS include:

  • Muscle twitches in the arms, legs, shoulders, or tongue
  • Muscle cramps
  • Spasticity (tight and stiff muscles)
  • Muscle weakness in an arm or leg
  • Slurred speech
  • Difficulty chewing

The first signs of ALS typically appear in one arm or leg. You may notice that simple tasks such as buttoning a shirt or typing at the computer become more difficult. If your leg is affected, you may trip or stumble more often.

Though the arms and legs are typically affected first, for some, the first ALS symptoms may appear as difficulty swallowing or trouble speaking.

Tracking Symptoms

If you experience any of these symptoms, it's important to take note of how long they have been occurring and if they have progressed so that you can discuss them with your healthcare provider.

Physical Examination

If you experience signs of ALS, your healthcare provider will likely conduct a physical examination, as well as ask questions about the history of your symptoms. They may also ask if anyone in your family has ALS or other diseases that affect the brain or spinal cord.

During the physical exam, your healthcare provider will test you for tight and stiff muscles, twitching muscles, muscle weakness, and loss of muscle mass or atrophy. They will also examine your reflexes to see if they respond faster than normal.

A provider will also look for another sign known as Babinski reflex. With this reflex, the big toe moves upward when the bottom of the foot is stroked.

This reflex typically disappears after the age of two unless there is neurological damage, like the kind that occurs with ALS.

Labs and Tests

After a physical exam, your healthcare provider may order several tests that can help with the diagnosis. Blood work will most likely be done to help exclude other causes of symptoms, such as thyroid disorders or low vitamin B12 levels.

The most common test used for suspected ALS is an electromyography (EMG). This test involves sensors and an electric current placed through a needle into the muscle that looks at the signals that run between nerves and muscles.

In ALS, there is a distinct pattern of electrical activity in the muscles and nerves. If this pattern is seen, your provider will order other tests to confirm the diagnosis.

In some cases, a muscle biopsy may also provide information that can lead to or exclude an ALS diagnosis. Genetic testing can also be performed.

Sometimes your provider may order a spinal tap (lumbar puncture), which removes a sample of fluid surrounding the spinal cord for examination in a lab.


An MRI (magnetic resonance imaging) of the brain and spinal cord can also be used in the diagnosis of ALS.

While MRI images of the brain or spinal cord are not reliable enough to diagnose ALS, they are helpful in ruling out other diseases, such as multiple sclerosis (MS) or a brain tumor.

Differential Diagnosis

Since there is not one specific test for ALS, diagnosing ALS is often a diagnosis of exclusion. This means that if your healthcare provider suspects you have ALS, they will conduct tests to rule out all possible causes of your symptoms before officially diagnosing you with ALS.

Other diseases that cause similar symptoms to ALS include, but are not limited to:

  • Cervical spine disease
  • Brain or spinal cord tumor
  • Vitamin B12 deficiency
  • Multiple sclerosis (potentially disabling autoimmune disease causing nerve damage between the brain and body)
  • Myasthenia gravis (autoimmune disease destroying nerve and muscle communication)
  • Lead poisoning
  • Thyroid disorders
  • Cervical spondylosis (age-related wear and tear of the neck’s spinal disks)

Testing for these other diseases and syndromes will help your healthcare provider pinpoint a precise diagnosis.


Since an ALS diagnosis is a diagnosis of exclusion, experiencing one or more of the symptoms does not necessarily mean you have ALS. However, it is important to know the signs and symptoms of the disease so that you can note them and talk to your healthcare provider about your concerns. If ALS is suspected, your provider will conduct a physical exam and order other specific tests, such as an EMG, muscle biopsy, or MRI.

A Word From Verywell

Diagnosing ALS is not always straightforward and can take some time. Experiencing symptoms of ALS will naturally cause some fear and concern. Talking to your healthcare provider about these concerns can help you work through it. If a diagnosis of ALS is confirmed, seeking the aid of a qualified mental health provider—or finding a support group in your area—can help you adjust to your life with ALS.

Receiving the news of an incurable disease is never easy, but keeping the lines of communication open with your healthcare team, friends, and family can ease some of the fear and anxiety that may come with an ALS diagnosis.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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