Difference Between Multiple Sclerosis and Myasthenia Gravis

by Joanne Marie, Demand Media Google

Multiple sclerosis, or MS, and myasthenia gravis are two neuromuscular disorders that are believed to have an autoimmune cause. In both MS and myasthenia gravis, an error in a person's immune system can cause the body to attack certain tissues, a situation that leads to symptoms involving muscle function. However, in spite of this similarity, the two disorders are also different in several ways.


Myasthenia gravis is caused by a problem at microscopic spots called neuromuscular junctions, where nerves end on the surface of muscle cells. Normally, a muscle contracts when a nerve releases a neurotransmitter called acetylcholine at this site, where muscle binding sites, or receptors, take up the neurotransmitter. In this disorder, immune cells make substances called antibodies that alter these binding sites, rendering them nonfunctional. Although the exact cause is not well understood, researchers suspect that an error in the thymus gland, an important immune organ, may be the culprit.
Although MS is also believed to be an autoimmune disorder, the underlying mechanisms are less well understood. In MS, the body's immune cells attack and gradually destroy a substance called myelin, an insulating material that covers nerve processes that transmit impulses to muscles. A paper published in June 2005 in the "Journal of Neuroscience Research" reviews the evidence for immune system involvement and lists several types of immune cells probably involved in MS.


Although any muscle may be affected by myasthenia gravis, those that control eye movements, facial expressions or swallowing are often affected. Sometimes, weak muscles cause swallowing problems or slurring of speech, a drooping eyelid, blurred or double vision, or a change in facial appearance. Symptoms vary greatly among people with this disorder, but may also involve weakness in the limbs that can cause unstable gait. In MS, some of the same symptoms may appear, including double vision or weakness in the arms and legs. But MS often causes other types of symptoms in addition to weakness, including paresthesias, which are feelings of numbness and prickling, or "pins and needles." People with MS can also feel pain in their muscles and sometimes have tremors or dizziness. Although symptoms of MS and myasthenia gravis overlap somewhat, diagnostic tests can usually distinguish between the two disorders.


In both myasthenia gravis and MS, symptoms often appear gradually over several months to a year or two, making diagnosis a challenge in some cases. For a person with new onset of weakness, a doctor will assess whether it's accompanied by changes in sensation, which doesn't usually occur in myasthenia gravis but often appears in MS. Several blood tests can help diagnose myasthenia gravis, including detecting antibodies against the acetylcholine receptor or another antibody called anti-MuSK, although in some cases, patients don't produce these. Other testing, including an electrical measurement of muscle-nerve interaction or testing after use of a drug to enhance acetylcholine can help make the diagnosis. For MS, a doctor uses several criteria to diagnose the disorder, including a detailed neurological exam, a careful medical history, spinal fluid analysis and magnetic resonance imaging, or MRI, of the brain and spinal cord. However, unlike myasthenia gravis, no blood test is currently available to definitively diagnose MS.


A great deal of research has been focused on both disorders. For MS, areas of exploration include finding new ways to diagnose the disorder by identifying specific changes in patients' MRIs, research reviewed in 2012 in "Expert Opinion in Medical Diagnostics." Other MS research includes development of new treatment approaches, such as use of specially designed antibodies to slow or stop progress of the disorder, as reviewed in depth in the March 2013 issue of "Expert Reviews in Neurotherapy."
For myasthenia gravis, a great deal of research is aimed at identifying effective new treatments. Although use of steroids and other medications that affect the immune system can be helpful, research such as that published in the January 2013 issue of "Drug Design, Development and Therapy" is focused on new drugs that block an enzyme that degrades acetylcholine, helping the neurotransmitter last longer and strengthening muscle contractions.
If you have questions about either MS or myasthenia gravis, discuss them with your physician, who is the best source of information about these disorders.

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