Multiple sclerosis (MS) – also known as disseminated sclerosis or encephalomyelitis disseminata – is an inflammatory disease in which the insulating covers – the myelin – of nerve cells in the brain and spinal cord are damaged. This disrupts the ability of parts of the nervous system to communicate resulting in a range of signs and symptoms, including impaired muscle control, visual disturbances, balance abnormalities, and impaired sensation as well as psychiatric problems. MS is an autoimmune disorder where the body’s own immune system attacks and destroys the myelin sheath covering nerves of the brain and spinal cord, a process termed demyelination.
MS takes several forms, with new symptoms occurring in isolated attacks (relapsing MS) or building up over time (progressive MS). Between attacks, symptoms may go away completely; however, permanent neurological problems often occur, especially as the disease advances.
MS gets its name from the build-up of scar tissue (sclerosis) in the brain and/or spinal cord. This scar tissue or plaques form when the protective and insulating myelin sheath covering nerves is destroyed, a process called demyelination. Without the myelin, electrical signals transmitted throughout the brain and spinal cord are disrupted or halted. The brain then becomes unable to send and to receive messages and it is this breakdown of communication that causes the symptoms of MS.
Although nerves have the capacity to regain myelin, this process is not sufficiently fast to keep pace with rate of demyelination. The types of symptoms, their severity, and the course of the disease varies widely, partly reflecting the location of the scar tissue and the extent of demyelination.
A 2009 survey suggested that there are about 24,000 MS sufferers in Australia, equivalent to 0.1% of the population. Worldwide, there are between 2 and 2.5 million sufferers, including 400,000 in the the United States alone, making MS the second most frequent cause (after trauma) of neurological disability beginning in early to middle adulthood.
MS is two to three times as common in females as in males and its occurrence is unusual before adolescence.
There is no known cause for MS. MS is up to 10 times more common in individuals who live far from the equator and for MS sufferers, flare-ups occur less frequently in the summer than at the end of winter. This and other evidence suggests a link between MS, latitude and exposure to sunlight via a mechanism that involves vitamin D.