Tests and diagnosis

By Mayo Clinic Staff

Amyotrophic lateral sclerosis (ALS) is difficult to diagnose early because it may appear similar to several other neurological diseases. Tests to rule out other conditions may include:

  • Electromyogram (EMG). During an EMG, your doctor inserts a needle electrode through your skin into various muscles. The test evaluates the electrical activity of your muscles when they contract and when they're at rest.

    Abnormalities in muscles seen in an electromyogram can help doctors diagnose ALS, or determine if you have a muscle or nerve condition that may be causing your symptoms. It can also help guide your exercise therapy.

  • Nerve conduction study. This study measures your nerves' ability to send impulses to muscles in different areas of your body. This test can determine if you have nerve damage or certain muscle diseases.
  • Magnetic resonance imaging (MRI). Using radio waves and a powerful magnetic field, an MRI can produce detailed images of your brain and spinal cord. An MRI can evaluate if you have spinal cord tumors, herniated disks in your neck or other conditions that may be causing your symptoms.
  • Blood and urine tests. Analyzing samples of your blood and urine in the laboratory may help your doctor eliminate other possible causes of your signs and symptoms.
  • Spinal tap (lumbar puncture). Sometimes a specialist may remove a sample of your spinal fluid for analysis. In this procedure, a specialist inserts a small needle between two vertebrae in your lower back and removes a small amount of cerebrospinal fluid for testing in the laboratory.
  • Muscle biopsy. If your doctor believes you may have a muscle disease rather than ALS, you may undergo a muscle biopsy. In this procedure, while you're under local anesthesia a small portion of your muscle is removed and sent to a lab for analysis.
Apr. 09, 2014