I also started losing the use of my left leg. My doctor's first MRI was also for MS, which was negative. Then I had MRI's on my back and spine- negative. I then went to a local neurologist and had an EMG, still nothing. After quite a few visits and almost 2 years after the onset I was referred to a neurologist who specializes in dystonia. That's what it is.
I get botox injections to relieve some of the muscle movement. It doesn't go away completely but helps somewhat. However this has affected every area of my life. I also developed drop foot and wear a brace.
The issue is that not too many doctor's even know what dystonia is so they can't diagnoze it. I was really lucky to get this doctor, he's great!