The symptoms of MS depend on which areas of the brain and spinal cord develop MS lesions. For example, if the nerve that is involved in vision (the optic nerve) develops a lesion, blurring of vision occurs. This is referred to as optic neuritis. If a lesion develops in the part of the brain that produces movement on the left side of the body, left-sided weakness develops. In addition to visual blurring and weakness, other common MS symptoms include fatigue, depression, urinary difficulties, walking unsteadiness, stiffness in the arms or legs, tingling, and numbness.

The time course over which MS lesions develop and the number and location of lesions is different for each individual. Consequently, the time frame in which symptoms occur and the specific types of symptoms experienced is unique for each person. Also, as a result of the large variability of lesions between individuals, MS varies greatly in severity. Some people may have rare, mild attacks over their lifetime and may not experience any permanent symptoms, while others may develop severe, permanent symptoms over a relatively short period of time.

MS symptoms may occur episodically or may progress continuously. Episodes of symptoms are known as relapses, attacks, or exacerbations. There usually is improvement in symptoms after an attack; this improvement is referred to as a “remission.” In contrast to these “relapsing-remitting” symptoms, some people have symptoms that develop slowly and then progressively worsen over time with no clear remissions; these symptoms are referred to as “progressive.”