Diagnosis

Amyotrophic lateral sclerosis is difficult to diagnose early because it can mimic other neurological diseases. Tests to rule out other conditions might include:

• Electromyogram (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 EMG can help doctors diagnose or rule out ALS. An EMG 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 or nerve diseases.
• MRI. Using radio waves and a powerful magnetic field, an MRI produces detailed images of your brain and spinal cord. An MRI can reveal spinal cord tumors, herniated disks in your neck or other conditions that might be causing your symptoms.
• Blood and urine tests. Analyzing samples of your blood and urine in the laboratory might help your doctor eliminate other possible causes of your signs and symptoms.
• Spinal tap (lumbar puncture). This involves removing a sample of your spinal fluid for laboratory testing using a small needle inserted between two vertebrae in your lower back.
• Muscle biopsy. If your doctor believes you may have a muscle disease rather than ALS, you might undergo a muscle biopsy. While you're under local anesthesia, a small portion of your muscle is removed and sent to a lab for analysis.