Multiple sclerosis – Wikipedia, the free encyclopedia

Multiple sclerosis (MS), also known as disseminated sclerosis or encephalomyelitis disseminata, is an inflammatory disease in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This damage disrupts the ability of parts of the nervous system to communicate, resulting in a wide range of signs and symptoms,[1][2] including physical, mental,[2] and sometimes psychiatric problems.[3] MS takes several forms, with new symptoms either occurring in isolated attacks (relapsing forms) or building up over time (progressive forms).[4] Between attacks, symptoms may go away completely; however, permanent neurological problems often occur, especially as the disease advances.[4]

While the cause is not clear, the underlying mechanism is thought to be either destruction by the immune system or failure of the myelin-producing cells.[5] Proposed causes for this include genetics and environmental factors such as infections.[2][6] MS is usually diagnosed based on the presenting signs and symptoms and the results of supporting medical tests.

There is no known cure for multiple sclerosis. Treatments attempt to improve function after an attack and prevent new attacks.[2] Medications used to treat MS while modestly effective can have adverse effects and be poorly tolerated. Many people pursue alternative treatments, despite a lack of evidence. The long-term outcome is difficult to predict, with good outcomes more often seen in women; those who develop the disease early in life; those with a relapsing course; and those who initially experienced few attacks.[7]Life expectancy is 5 to 10 years lower than that of an unaffected population.[1]

As of 2008, between 2 and 2.5 million people are affected globally with rates varying widely in different regions of the world and among different populations.[8] The disease usually begins between the ages of 20 and 50 and is twice as common in women as in men.[9] The name multiple sclerosis refers to scars (scleraebetter known as plaques or lesions) particularly in the white matter of the brain and spinal cord.[10] MS was first described in 1868 by Jean-Martin Charcot.[10] A number of new treatments and diagnostic methods are under development.

A person with MS can have almost any neurological symptom or sign; with autonomic, visual, motor, and sensory problems being the most common.[1] The specific symptoms are determined by the locations of the lesions within the nervous system, and may include loss of sensitivity or changes in sensation such as tingling, pins and needles or numbness, muscle weakness, very pronounced reflexes, muscle spasms, or difficulty in moving; difficulties with coordination and balance (ataxia); problems with speech or swallowing, visual problems (nystagmus, optic neuritis or double vision), feeling tired, acute or chronic pain, and bladder and bowel difficulties, among others.[1] Difficulties thinking and emotional problems such as depression or unstable mood are also common.[1]Uhthoff's phenomenon, a worsening of symptoms due to exposure to higher than usual temperatures, and Lhermitte's sign, an electrical sensation that runs down the back when bending the neck, are particularly characteristic of MS.[1] The main measure of disability and severity is the expanded disability status scale (EDSS), with other measures such as the multiple sclerosis functional composite being increasingly used in research.[11][12][13]

The condition begins in 85% of cases as a clinically isolated syndrome over a number of days with 45% having motor or sensory problems, 20% having optic neuritis, and 10% having symptoms related to brainstem dysfunction, while the remaining 25% have more than one of the previous difficulties.[14] The course of symptoms occurs in two main patterns initially; either as episodes of sudden worsening that last a few days to months (called relapses, exacerbations, bouts, attacks, or flare-ups) followed by improvement (85% of cases) or as a gradual worsening over time without periods of recovery (10-15% of cases).[9] A combination of these two patterns may also occur[4] or people may start in a relapsing and remitting course which then becomes progressive later on.[9] Relapses are usually not predictable, occurring without warning.[1] Exacerbations rarely occur more frequently than twice per year.[1] Some relapses, however, are preceded by common triggers and they occur more frequently during spring and summer.[15] Similarly, viral infections such as the common cold, influenza, or gastroenteritis increase their risk.[1]Stress may also trigger an attack.[16] Being pregnant decreases the risk of relapse; however, during the first months after delivery the risk increases.[1] Overall, pregnancy does not seem to influence long-term disability.[1] Many events have not been found to affect relapse rates including vaccination, breast feeding,[1] physical trauma,[17] and Uhthoff's phenomenon.[15]

The cause of MS is unknown; however, it is believed to occur as a result of some combination of environmental factors such as infectious agents and genetics.[1] Theories try to combine the data into likely explanations, but none has proved definitive. While there are a number of environmental risk factors and although some are partly modifiable, further research is needed to determine whether their elimination can prevent MS.[18]

MS is more common in people who live farther from the equator, although exceptions exist.[1][19] These exceptions include ethnic groups that are at low risk far from the equator such as the Samis, Amerindians, Canadian Hutterites, New Zealand Mori,[20] and Canada's Inuit,[9] as well as groups that have a relatively high risk close to the equator such as Sardinians,[9]Palestinians and Parsis.[20] The cause of this geographical pattern is not clear.[9] While the north-south gradient of incidence is decreasing,[19] as of 2010 it is still present.[9]

MS is more common in regions with northern European populations[1] and the geographic variation may simply reflect the global distribution of these high-risk populations.[9] Decreased sunlight exposure resulting in decreased vitamin D production has also been put forward as an explanation.[21][22] A relationship between season of birth and MS lends support to this idea, with fewer people born in the northern hemisphere in November as compared to May being affected later in life.[23] Environmental factors may play a role during childhood, with several studies finding that people who move to a different region of the world before the age of 15 acquire the new region's risk to MS. If migration takes place after age 15, however, the person retains the risk of his home country.[1][18] There is some evidence that the effect of moving may still apply to people older than 15.[1]

MS is not considered a hereditary disease; however, a number of genetic variations have been shown to increase the risk.[24] The probability is higher in relatives of an affected person, with a greater risk among those who are more closely related.[2] In identical twins both are affected about 30% of the time, while around 5% for non-identical twins and 2.5% of siblings are affected with a lower percentage of half-siblings.[1][2][25] If both parents are affected the risk in their children is 10 times that of the general population.[9] MS is also more common in some ethnic groups than others.[26]

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Multiple sclerosis - Wikipedia, the free encyclopedia