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.

Therefore, your doctor will perform a physical exam to investigate:

Muscle weakness
Muscle twitching
Unusual responses to reflex testing
Muscle loss, tightness or a decrease in muscle size
Slurred or slow speech, and other signs of weakness around the mouth and tongue
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 tests

Blood, urine and spinal fluid can be tested to rule out diseases that may cause similar symptoms to 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 categorized further based on family history:
Familial ALS

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

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

However, the categorization into fALS and sALS may be an oversimplification. 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; they may be able to participate in clinical research trials and may be more informed about longer-term life choices.

Genetic testing

If another family member has been diagnosed with ALS in the past, a small blood or saliva sample is usually taken to perform a genetic test. Genetic testing can provide a deeper understanding of your ALS.

In particular:

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 emotional, social, or financial consequences of obtaining a genetic test.

  • The possibility of genetic discrimination in employment, as well as for disability or life insurance, can also be a concern for someone living with ALS.

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 in detail the benefits, risks, and limitations of genetic testing to you.