Before a person develops multiple sclerosis, he or she may experience what's known as a clinically isolated syndrome, or CIS. This is a single event that indicates dymelination is taking place in certain nerves. Examples of a CIS include an attack of optic neuritis (leading to vision problems in one eye), or an episode of numbness on one side of the body. When a CIS occurs, there are no other clinical signs or symptoms present.

Those who experience a clinically isolated syndrome may or may not go on to develop multiple sclerosis. When MS does develop, it can progress in a variety of ways.

Multiple sclerosis progresses differently for each person, and there's no way to predict which course the disease will take. But MS generally follows one of three basic patterns:

* Relapsing-remitting

* Primary-progressive

* And secondary-progressive

Another form of the disease, known as benign MS, can also occur. Let's take a look at each of these patterns.

In relapsing-remitting MS, you have unpredictable attacks, called "exacerbations," where your symptoms suddenly get worse. These attacks take place over several days to weeks. After each attack, it can take weeks to months to recover all (or even just part) of your previous abilities. Relapsing-remitting MS usually occurs early in the course of the disease for most people. About 85% of people with MS have this form of the disease.

In primary-progressive MS, there is a gradual but steady worsening of your symptoms. There are no obvious exacerbations or periods of remission. Only 10-15% of all people with MS have this form of the disease. However, it's the most common type of multiple sclerosis in people who get the disease after age 40.

Secondary-progressive MS begins with a relapsing-remitting pattern, but later turns into a progressive version of the disease -- with the symptoms gradually getting worse. The progressive part of the disease can start shortly after the MS begins, or it can happen years or even decades later.

In addition to the main patterns of MS, 20% of the people with multiple sclerosis have a benign form of the disease. In benign MS, a person's symptoms do not get any worse after the initial attack, or only get a little worse. People with benign MS remain fully functional.