Multiple sclerosis (MS) is a chronic neurological disease that involves the central nervous system—specifically the brain, spinal cord, and optic nerves. MS can cause problems with muscle control and strength, vision, balance, sensation, and mental functions.

The brain, spinal cord, and optic nerves are connected to one another by nerves and nerve fibers. A protein coating called myelin surrounds and protects the nerve fibers. When myelin becomes inflamed or is destroyed—this is called demyelination—the result is an interruption in the normal flow of nerve impulses through the central nervous system. The process of demyelination and subsequent disruption of nerve impulse flow is the disease known as MS.

Injured tissue called lesions or plaques form in areas of demyelination. In many cases, the cells (oligodendrocytes) that create myelin are destroyed, as are the nerve fibers (axons). The body is then not able to heal the myelin or nerve fibers, which further contributes to disability.

Generally, MS follows one of four courses, which are called: 1

    * Relapsing-remitting, where symptoms may fade and then recur at random for many years.
    * Secondary progressive, which initially follows a relapsing-remitting course. Later on, it becomes steadily progressive.
    * Primary progressive, where the disease is progressive from the start.
    * Progressive relapsing, where steady deterioration of nerve function begins when symptoms first appear. Symptoms appear and disappear, but nerve damage continues.

What causes multiple sclerosis?

The cause of MS is unknown. There may be a genetic link because a person's risk of MS is higher when a parent has MS. 2

Geographic location also may play a role. MS is more prevalent in colder regions that are further away from the equator. 3 Researchers have made a connection between a person's geographic location during childhood and the risk of MS later in life, suggesting that a childhood viral illness or other environmental factors may make a person more likely to develop the disease.

Some evidence suggests that people who move from a high-risk area to a low-risk area, or the reverse, before the age of 15 take on the risk associated with their new area. If they are older than 15, they retain the risk associated with their old area.

A problem with the immune system occurring early in life may trigger the onset of MS in some people. The "trigger" may be a viral infection. In susceptible people, the viral infection may start an autoimmune reaction in which the immune system attacks its own myelin.
What are the symptoms of MS?

Symptoms vary according to which parts of the central nervous system—including the brain, spinal cord or optic nerves—are damaged by inflammation and the destruction of myelin. Symptoms similar to those of MS can occur with other conditions and do not necessarily mean you have MS.

The most common early symptoms of MS include:

    * Muscle symptoms—muscle weakness, leg dragging, stiffness, a tendency to drop things, a feeling of heaviness, clumsiness, or a lack of coordination.
    * Visual symptoms—blurred, foggy, or hazy vision, eyeball pain (especially with movement), blindness, or double vision. Optic neuritis (a sudden loss of vision and eye pain) is a fairly common initial symptom, occurring in up to 23% of those who develop MS. 2

Less common early symptoms include:

    * Sensory symptoms—tingling, a pins-and-needles sensation, numbness, a bandlike tightness around the trunk or limbs, or electrical sensations moving down the back and limbs.
    * Balance symptoms—lightheadedness or dizziness, and a spinning feeling (vertigo).

As MS progresses, symptoms may include stiff movement (spasticity), tremors, pain, difficulty controlling urination, depression, and difficulty thinking clearly (cognitive impairment).
How is multiple sclerosis diagnosed?

MS is diagnosed when lesions (injured tissue from demyelination) occur in more than one area of the central nervous system at different times—meaning a neurologist can verify that you had at least two episodes of MS. Each episode must have lasted at least 24 hours, and be confirmed by neurological examination or neurological tests. Symptoms alone do not necessarily mean you have MS. 4

If you have MS, a magnetic resonance image (MRI) test usually shows changes in more than one area of the central nervous system that have developed at more than one point in time. Not all changes seen on an MRI scan indicate MS, but criteria have been developed for diagnosing MS with MRI.

The diagnosis can be difficult to make because early symptoms are usually vague.