How ALS is diagnosed

Unfortunately, there is no single test that can diagnose ALS, and the symptoms can vary from person to person. A combination of a person’s family history, a physical exam and various tests may be used to make a diagnosis. Read below to learn more about what may be involved in the diagnostic process.

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History and physical exam

ALS symptoms can vary from person to person, so it is important to define exactly what symptoms are occurring. A thorough history is a crucial part of the diagnostic process, as it can provide important information about disease progression, family links, and relevant health issues.

Your doctor will ask questions about your symptoms, health, and family history.

The most common symptom of ALS is slowly worsening muscle weakness, which is usually painless. Other symptoms might include tripping or falling, dropping objects, fatigue in the arms or legs, slurred speech, and uncontrollable periods of laughing or crying.

After taking your medical history, your doctor will perform a physical exam to investigate:

Laboratory tests

To rule out other possible causes of your symptoms, some of the following tests may be performed on an individual basis and at the discretion of your doctor.

Blood, urine, and spinal fluid can be tested to rule out diseases that may cause symptoms similar to those of ALS.

Nerve testing

If the history, physical exam, and laboratory testing indicate that ALS may be the cause of the symptoms, the next step is usually to perform electromyography, or EMG.

This test measures what happens when the nerves within the muscle are stimulated by a small amount of electricity. This response is measured and can be useful to determine whether the nerves are functioning properly.

Imaging tests

Imaging tests may be used to rule out other disorders that may mimic ALS. Following clinical assessment, it may be useful to perform imaging tests on the brain and spinal cord.

After the diagnosis

Historically—once ALS has been confirmed as the cause of your symptoms—your diagnosis could be further categorized, based on family history:

Familial ALS

People with a known family history of ALS are defined as having familial ALS (fALS)

Sporadic ALS

Those with no family history present are defined as having sporadic ALS (sALS)

However, genetic forms of ALS have been identified in those with a family history of ALS as well as in those with no family history.


Genetic testing can help both patients with fALS and sALS to better understand their diagnosis so they can make better informed life choices and potentially take part in clinical trials.

Genetic testing

A genetic test is as simple as providing a blood or saliva sample, but can offer invaluable information such as:

Why ALS has developed

Whether or not family members are at risk, including whether it can be passed on to children

How quickly the disease may progress

Whether the person diagnosed could be eligible for clinical trials exploring new approaches to care

Potential risks of genetic testing

While the physical risks associated with genetic testing may be minimal, there can be an impact to a patient's:

  • Emotional well-being
  • Employment, due to genetic discrimination
  • Disability or life insurance

For these reasons, you may be referred to speak with a genetic counselor before, during, and after receiving genetic testing results. A genetic counselor can further explain to you in detail the benefits, risks, and limitations of genetic testing.