fewer symptoms and slower progression of m.s. than patients with lower levels, especially in the early stages of the disease. over the years, this broadcast has been to a lot of places, but never to where dr. jon lapook is taking us tonight. we're going inside the trial and approval process for an experimental treatment for m.s.. >> reporter: 11 years ago, megan quinn had just got married and was the picture of health. >> i used to run five miles a day. all of a sudden on my third mile i started dragging my foot. i didn't understand, i thought okay, i'm getting old and tired. i was 27 years old. but nothing ever occurred to me something was wrong. >> reporter: the diagnosis was multiple sclerosis. the multiple sclerosis-- or m.s. is an autoimmune disease where the body attacks itself and damages myelin, the protective covering surrounding nerve cells. with that insulation compromises the nerves deteriorate and can cause a wide range of symptoms including visual problems,