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What is multiple sclerosis?

Multiple sclerosis (MS) is a chronic disease that affects the central nervous system (CNS), which includes the brain, spinal cord and optic nerves. It causes inflammation and the destruction of myelin. Myelin surrounds nerve fibers and acts like insulation on a wire, preventing “short-circuits” that divert a nerve signal from having its desired effects. The “demyelination” process interferes with nerve impulse transmission, affects muscular control, and causes a variety of sensory, motor, and psychological symptoms. Damage to the myelin usually resolves with time and symptoms subside, but repeated attacks can lead to a continual process of demyelination and remyelination, which produces nerve fiber scarring and progressive disability.

The cause of MS is unknown. It is thought to be an autoimmune process triggered by a virus or environmental factors (such as low vitamin D and cigarette smoking), and genetics are thought to play a significant role.

Typically, MS first appears and is diagnosed when individuals are between 20 and 40 years of age, although it can occur in young children. Two to three times more women are affected than men. It is more common in Northern European Caucasians than other ethnic groups and is seen in greater numbers in people who live in temperate climates rather than warm or cold ones.

According to the National Multiple Sclerosis Society, as of 2019, MS affects about one million adults in the United States, which is 50% more than originally thought. Worldwide, more than 2.3 million have a diagnosis of MS.

The risk of developing this disease is estimated to be about 3.5 in 1,000, or less than half of one percent, in the U.S. In families with an affected member, the risk increased to three to four percent. It is about 31% for the identical twin of an affected person, strengthening the notion of a genetic component to the cause.

There is no single test that can conclusively diagnose MS. Instead, healthcare practitioners look for a combination of factors to determine if a patient has MS. The factors are described in a document called the “McDonald Criteria,” named for the doctor who chaired the 2001 panel of experts charged with establishing criteria for an accurate diagnosis. The document is updated regularly as new research improves our understanding of the disease, speeds the diagnosis, and reduces misdiagnosis. Physicians will consult a patient’s medical history and a variety of clinical and laboratory tests to aid in their diagnosis. In applying the criteria for diagnosing MS, a healthcare practitioner must:

  • Determine the number of attacks
  • Determine that the CNS has been damaged in at least two places
  • Confirm that the damage occurred at separate times, more than one month apart
  • Rule out other conditions that cause a similar set of signs and symptoms

Once diagnosed, an individual may be classified as having one of several types of MS, based on signs and symptoms, frequency of relapses, rate of disease progression, and the number of areas that are damaged in the CNS:

  • Clinically Isolated Syndrome (CIS)
  • Relapsing-Remitting MS (RRMS)
  • Secondary-Progressive MS (SPMS)
  • Primary-Progressive MS (PPMS)


About Multiple Sclerosis

Signs and Symptoms

The onset of MS symptoms is called an attack. Recovery from symptoms is referred to as remission. A return of symptoms is called a relapse.

Because MS can attack any area of the central nervous system, the signs and symptoms of MS are many and varied and may be mild or severe. The types of symptoms experienced depend on the nerves affected and what they are responsible for controlling. Symptoms of MS may come and go, and their duration may last from days to months. Some examples include:

  • Sensory symptoms such as numbness, tingling, pain, burning, itching, facial pain, and visual disturbances
  • Numbness or weakness in one or more limbs that typically occurs on one side of your body at a time, or the legs or trunk
  • Electric-shock sensations that occur with certain neck movements, especially when bending the neck forward
  • Motor symptoms such as speech impediments, muscle stiffness and weakness, tremor, difficulty walking, lack of coordination
  • Problems with sexual, bowel and bladder function
  • Dizziness that doesn’t go away
  • Psychological symptoms such as mood swings, depression, and problems with thinking, learning, and memory
  • Fatigue occurs in up to 80% of those with MS.

According to the National Multiple Sclerosis Society, about 85% of those with multiple sclerosis initially have relapsing-remitting MS. This means they experience periodic attacks or relapses, followed by healing and symptom remission. Later in the course of the disease, about 50% develop secondary-progressive MS. Their symptoms and disabilities worsen as they continue to have relapses but do not fully recover. About 15% develop primary-progressive MS, where symptoms gradually worsen without experiencing remissions.


Although there is no single test or set of tests that can establish a diagnosis of multiple sclerosis (MS), there are three tests that are generally considered useful:

Laboratory tests
There are no laboratory tests that are completely specific for MS, but several laboratory tests are helpful in diagnosing or excluding this disease as the cause of a person’s signs and symptoms. A few involve tests done on cerebrospinal fluid:

  • CSF Electrophoresis and Isoelectric Focusing—these are two methods for separating the proteins in a biological fluid. A patient’s CSF and serum are evaluated side-by-side. Following the separation step, a protein stain is applied to both specimens and the banding patterns that appear in the CSF and serum are compared. The presence of two or more IgG bands in CSF that are not present in serum is a positive test for oligoclonal banding. About 90% of people with MS show oligoclonal banding in their CSF.
  • CSF Immunoglobulin G (IgG) Index—increased levels of CSF IgG can be due to excess production of IgG within the central nervous system, which is seen with MS and several other diseases. It can also be due to leakage of plasma proteins into the CSF, such as might occur with inflammation or trauma. To discriminate between these two possibilities, the IgG index is calculated from IgG and albumin measurements performed in CSF and serum:IgG index = [IgG (CSF) / IgG (serum)] / [Albumin (CSF) /Albumin (serum)]An elevated IgG index indicates increased production of IgG within the central nervous system. It is found in about 90% of MS cases.
  • Myelin basic protein—this is a major component of myelin. Increased concentrations of myelin basic protein in CSF indicate that demyelination is taking place. This process is not specific for MS, as other inflammatory diseases of the central nervous system can also elevate the amount of myelin basic protein in CSF. This test is not widely available; however, it may be used to assess disease activity in cases of established MS.

Healthcare practitioners may also test for diseases that can cause symptoms similar to MS to determine if they may be responsible for a patient’s illness. Examples include:

Non-laboratory tests

  • MRI (magnetic resonance imaging) scans allow healthcare practitioners to examine the brain, spinal cord, and optic nerve. MRI can show both permanent CNS scarring as well as new lesions. These scans are used to help diagnose MS and to track its progression over time. Improvements in MRI technology have significantly improved the ability to accurately diagnose MS at an early stage. Early diagnosis and treatment is key to minimizing the effects of the disease.
    In addition to the standard MRI, there are a variety of specialized techniques that may be performed, such as functional MRI, magnetic resonance spectroscopy, and diffusion-tensor MRI. The National Multiple Sclerosis Society (NMSS) web site has more information on the use of MRI in MS.
  • Visual Evoked Potentials (VEP) are electrical diagnostic tests that measure the speed of nerve transmissions (messages) in various parts of the brain. They record the nervous system’s electrical response to visual stimuli. Damage to myelin can slow nervous system response time and VEP tests can reveal evidence of scarring along nerve pathways associated with vision. The NMSS web page has additional details about this test.
    Two other types of evoked potentials may be used, though less commonly: (1) Brainstem Auditory Evoked Potentials (BAEP) is a test that helps detect lesions in the brainstem causing delays in the transmission of sounds, and (2) Somatosensory Evoked Potentials (SSEP) is a test that applies a brief electrical stimulus to the wrist or ankle. It detects disruptions in the pathways from the arms and legs to the brain at very specific points of the CNS.


There is no cure for multiple sclerosis, but a variety of treatments are available that may be used to manage the condition. The goals of MS treatment are to slow the progression of the disease, relieve symptoms, and minimize the effects of acute attacks.

  • Several medications have been approved by the U.S. Food and Drug Administration (FDA) to help reduce the severity of the disease and slow progression. These are useful for many people with relapsing forms of MS. (For details, see the National Multiple Sclerosis Society webpage on Medications.)
  • Healthcare practitioners may prescribe corticosteroids for short periods of time to help reduce inflammation and shorten the duration of relapses.
  • Other medications may be used to address specific symptoms, such as bladder and bowel problems, tremors, dizziness, pain, and problems walking, to name a few. Fatigue and depression sometimes associated with MS, for example, may be treated with appropriate antidepressants.
  • Physical therapy, exercise, and avoiding heat are also important measures.

For more on specific medications that may be prescribed, see the Treatments page on the National Multiple Sclerosis Society website.

MS does not significantly decrease the lifespan of those who have it, but it can frequently and intermittently affect quality of life. While the vast majority of patients are mildly affected, the worst cases can render a person unable to write, speak, or walk. People with MS usually work with a team of professionals who help support and monitor their condition and address their changing needs. Current MS research is directed toward understanding the cause of MS in hopes of developing better drugs to treat, if not cure or prevent the disease.

View Sources

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