Well if you look it up, which I have done only very very briefly, you will encounter all sorts of horrific pictures and prognostications. But as with anything the actual personal experience is quite different to what one finds on the internet.
Basically it’s an extremely rare autoimmune disorder affecting only a few hundred thousand people. I’ve read that all autoimmune disorders have more in common than not: they are basically your immune system flaring up to attack something it shouldn’t be attacking. In this cause muscles (the myositis) and skin (the derma). Surprisingly, to me, most of the online mentions seem to focus on the skin aspect and mention the muscles secondary. Hello? I’d much rather have skin rash then degenerating muscles! That’s the horrible part. Also the derma part is quite mild for me, it’s basically unnoticeable unless you are looking for it. But muscles degenerating to the point that you can barely get in and out of the car or walk up the stairs: that’s noticeable.