Multiple Sclerosis Health Article

MULTIPLE SCLEROSIS

Multiple sclerosis (MS) is a disorder that affects primarily the myelinated white matter of the central nervous system (CNS), the brain, optic nerves, and spinal cord. There is no known cause. Myelin is the fatty sheath that insulates nerve fibers (axons). Partial or complete loss of myelin due to MS impairs nerve conduction through affected axons, producing symptoms and functional impairment referable to them. Thus, MS may produce mild to severe weakness, lack of coordination, disordered sensations, partial loss of vision, impaired control of bladder and bowel function, impaired cognition, or any combination of these effects.

Early in the course of the disorder, symptoms are often brief and transient—impaired function caused by a particular episode, or relapse, tends to improve, in what is called a "remission." Remissions may be partial or total. However, over the course of years, incomplete recovery from relapses may occur, leading to the accumulation of impaired function and producing some degree of disability in about 70 percent of affected individuals. Among those who become disabled, some do not experience improvement from the beginning. However, it is important to realize that, although it is a common cause of disability among young to middle-aged individuals, MS is very unpredictable in a particular person; it does not necessarily disable and it does not necessarily shorten life span appreciably.

The average age of occurrence of the first symptom(s) is thirty-three, but MS may show itself as early as childhood or as late as age sixty or beyond. It affects almost twice as many women as men, and primarily in men and women of predominantly or mixed Caucasian parentage. Approximately 350,000 people in the United States have MS, and it is estimated to affect about 3 million people worldwide. However, MS is rare among South and East Asians, and among blacks in Africa. These differences suggest that susceptibility to develop MS may be genetically determined. However, among identical twins where one has MS, no more than 50 percent of the unaffected twins will go on to develop MS. This lends support to the concept that an environmental trigger, perhaps a viral infection, acts in concert with the genetic setting to produce MS. Siblings and children of those with MS have a somewhat greater chance of developing MS, but no specific genetic pattern has been identified. It is likely that multiple genes are involved in conferring susceptibility.

The frequency of MS has been studied closely since the 1930s. However, despite improved diagnostic methods (and improved treatment), the incidence (number of new cases per year in the population) does not appear to have increased.

Even after many years of intensive research, the cause of MS remains elusive, and it is a challenging subject for research. The most widely accepted hypothesis at this time is that an infection triggers an autoimmune response in genetically susceptible individuals. Autoimmunity implies that the body's immune-defense system erroneously and inappropriately attacks normal tissues, in this case the myelin and/or the cell that synthesizes and supports myelin, the oligodendrocyte.

Diagnosing MS is often very challenging. To do so involves documenting the occurrence of two or more episodes of impaired function, occurring at different times, that are referable to CNS white matter, while excluding all other possible causes of the problems. The fact that MS affects primarily the CNS white matter makes it possible to visualize very accurately areas of inflammation and demyelination via magnetic resonance imaging (MRI). MRI is an invaluable aid to diagnosis, although the MRI picture alone is not sufficient to be certain of the diagnosis. MRI is also used to identify new relapses, and to quantify the number and size of past episodes. Similarly, the cerebrospinal fluid typically shows alterations that may support a diagnosis, but a diagnosis cannot be made without appropriate clinical history and neurological examination.

Even though its cause is still mysterious, treatments have been developed that have reduced the number of relapses by more than 30 percent. These agents include recombinant interferon beta (IFNß; particular brand names include Avonex, Betaseron, and Rebif) and glatiramer acetate (Copaxone), each of which is widely used. Laboratory and clinical studies of many other possible treatments are underway, which is a very hopeful indicator of more effective therapies to come in the future. In addition to these disease-modifying agents, treatment often includes the use of medications intended for purely symptomatic relief, as well as physical therapy and occupational therapy. The challenges posed by an uncertain clinical course, and by chronic disability among some individuals, makes psychological support a key part of management.

The National Multiple Sclerosis Society (http://nmss.org/), similar organizations in other countries, and the International Federation of Multiple Sclerosis Societies (http://www.who.int/ina-ngo/ngo/ngo076.htm) are excellent sources of further information about the disorder, ongoing research, and treatment.

DONALD H. SILBERBERG

(SEE ALSO: Environmental Determinants of Health; Genes; Genetic Disorders; Genetics and Health)