I think there is IS (unknown origin) and neuromuscular. I was classified in the IS group until I was diagnosed with dystonia and muscle disease. I think there are more dystonia patients out there like me. They see uneven shoulders and chalk it up to the scoliosis without looking at the musculature. Although, they did do an EMG study on my left arm when I was 16. I remember some very fine needles around my shoulder area, but they didn't get into my neck where all the pain was. They were looking for nerve damage instead of tight muscles that compressed those nerves. I was relaxed and put in a position where I was not in pain. They just missed it... They needed to look and my upper traps and neck more.