Geo, one of my professors in college has dermatomyositis and hers was diagnosed before she had any muscle weakness or damage. She was put on Prednisone which started to work, but she couldn't handle it and she was switched to Methotrexate. She takes it on Saturday and does great throughout the week. When she tries to go off it, though, her symptoms come back. The myopathies can be chronic and hers apparently is. If yours cleared up with Prednisone, well, I would be running to the neuro and rheumo. So, so, so many rheumos don't know all the "rare" diseases out there and don't test for them. Same with the dermatologists. I am surprised, though, that the neuro didn't pick up on your sympyoms.
Don't let them tell you that your emg and ck levels would have proven the diagnosis because I am living proof that that isn't true. My polymyositis did not show up on my first two emg's or my ck levels, but DID show up on muscle biopsy. Now my third emg was positive for it. That is the same as dermatomyositis minus the rash. I hate to hope this illness on you, but it is better than als. It's still devastating, but better and treatable. Good luck