Amyotrophic lateral sclerosis (ALS), commonly called Lou Gehrig's disease, causes progressive degeneration of the nerve cells in the brain and spinal cord. Patients suffering from ALS lose the ability to control muscle movements, including involuntary muscles needed for swallowing and breathing. Because the ALS Association reports that the life expectancy for patients with ALS is only two to five years, obtaining a diagnosis early can be critical to starting treatments that can help to prolong life. There is no one test to diagnose ALS, but many tests can help to rule out other diseases that may cause similar symptoms.
Electromyography
Electromyography is a test performed to help determine if the cause of muscle weakness is due to a primary muscle condition or a neurological disorder. This test is done by inserting a thin needle electrode hooked up to an oscilloscope into the muscle. When the patient contracts the muscle the electrode will read the electrical activity in the muscle and transmit it to the oscilloscope where it can be displayed.
At rest, normal muscle cells are silent; when contracted, electrical impulses are fired between nerves and muscle cells. A patient with ALS may have muscle spasms or twitching even at rest, sending electrical impulses that can be detected by the electromyography. In addition, because the nerves of ALS patients deteriorate, the muscles atrophy, or waste, from a lack of stimulation causing them to produce abnormally small impulses.
Nerve Conduction Velocity
A nerve conduction velocity test (NCV) involves placing electrodes on the skin over the nerve. Small electrical shocks are then delivered to the nerve through the electrode to induce a response. The speed and strength of the response provides information on the health of the nerve. The strength of the nerve response is directly proportional to the number of nerve fibers, according to the Muscular Dystrophy Association. Sine ALS causes nerves to degenerate, or break down, resulting in fewer nerve fibers, the nerve's electrical response is much smaller.
Magnetic Resonance Imaging
A magnetic resonance imaging (MRI) test is a non-invasive procedure that uses magnetic fields and radio waves to produce an image of the area of the body in question. Patients with ALS may not show any abnormalities on an MRI, but performing an MRI can detect other conditions such as a spinal cord tumor or cervical spondylosis which can produce symptoms similar to ALS. Ruling out these conditions help lead doctors to their diagnosis.
