DEAR MAYO CLINIC: My sister's doctor recently told her he suspects she may have MS, but she hasn't been definitively diagnosed with the disease. Isn't there a test that can tell if someone has MS? What are the common symptoms? Are some people at higher risk for getting MS than others?
ANSWER: Unfortunately, no one specific test can diagnose multiple sclerosis, or MS. Instead, the disease is diagnosed using a combination of exams and tests to identify MS and to rule out other conditions that may have similar signs and symptoms.
MS is a central nervous system disease. Your body's nervous system can be divided into two categories: central and peripheral. The central nervous system includes your brain, your spinal cord and your optic nerve. The peripheral nervous system includes all the nerves outside your central nervous system. MS affects the central nervous system. It does not affect the peripheral nervous system.
It's not exactly clear what causes this disease. But it appears that in people who have MS, the body's immune system attacks and strips away the fatty substance that coats and protects the nerve fibers. When this substance, called myelin, is destroyed and the nerve fiber is exposed, the nerve cannot work correctly.
In general, MS is more common in people of northwestern European descent. Women are much more likely than men to get MS; the ratio of women to men affected by MS is about 3 to 1. Some research suggests exposure to Epstein-Barr virus, the virus that causes mononucleosis, raises a person's risk for MS, as well.
The symptoms caused by MS depend on where the damaged nerves are located. For example, if the optic nerve is affected -- that's the bundle of nerve fibers that carry information from your eye to your brain -- it may cause blurred vision. Other common symptoms include numbness or weakness in an arm or leg, tingling or pain in one part of the body, lack of coordination, slurred speech and dizziness. For many people with MS, particularly in the early stages of the disease, symptoms are not consistent. They appear for some time, and then go away for a period of time.
Diagnosing MS can be challenging because its symptoms are similar to those of other nervous system diseases. In addition, no specific marker for MS has been identified. That means diagnosis is based on the combination of a physical exam, a person's medical history and symptoms, and a variety of tests.
Tests to diagnose MS may include blood tests and a spinal tap. These tests allow doctors to rule out other conditions, such as a viral infection or other inflammatory diseases. Magnetic resonance imaging, or MRI, also is needed in helping to identify MS.
MRI can show lesions that appear to be due to myelin loss. However, these types of lesions also can be caused by other conditions, such as lupus, migraine headaches and diabetes. So the presence of these lesions alone cannot be considered definitive proof of multiple sclerosis.
Another test used to diagnose MS measures the electrical signals sent by the brain in response to a stimulus. This test, called an evoked potential test, can help detect lesions or nerve damage in the optic nerve, brainstem or spinal cord even when there are no obvious symptoms of nerve damage.
MS behaves somewhat differently in every person. That makes it very important for the spectrum of tests used to diagnose MS to be tailored to an individual's situation. The results also need to be carefully considered along with findings from a physical exam and information gathered in the medical history. In most cases, it is only with this type of thorough evaluation that a health care team can confidently arrive at a diagnosis of MS. --Orhun Kantarci, M.D., Neurology,Mayo Clinic,Rochester, Minn.
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