“Multiple sclerosis (MS) happens when your immune system attacks myelin, the sheath around your nerve cells. Without this outer shell, your nerves become damaged and cause communication problems between your brain and the rest of your body.

MS is a chronic, or long-lasting, disease that can affect your brain, spinal cord, and the optic nerves in your eyes. It can cause problems with vision, balance, muscle control, and other basic body functions. 

The effects of MS vary from person to person. Some people have mild symptoms and don’t need treatment, while others have trouble getting around and doing daily tasks.”

WebMD (https://www.webmd.com/multiple-sclerosis/what-is-multiple-sclerosis)