I don't understand Myositis

Source:  I don't understand Myositis    Tag:  inclusion body myositis
Is it an inflammatory myopathy?
Is it a muscular dystrophy?
Is it an autoimmune condition?
I don't know and I don't know why one day the pain in the shoulders is SOOOO bad and 3 days later it is the wrists or the thighs. The frustrating thing is accepting that treatment is limited to pain management and expensive physical interventions.  The pain is so bad it makes you want to...