Welcome to the board, animallover4727. Sorry it is under such worrisome circumstances.
We've had members in the past whose dogs have had this disease--but I'm not sure if any of them are still current.
That being said, there are other reasons for the head muscles to atrophy, and maybe your dog has something other than MMM. I'll cross my fingers that the vets find something other than MMM that's easily treated.
Please let us know what the vets say?