You list the typical symptoms that accompany myositis diseases. There are 3 types, polymyositis, dermatomyositis and inclusion body myositis. PM attacks the muscle cells directly and DM attacks the vessels in the cells but the pattern of weakness around the hip and shoulder girdles are the same but there are usually skin manifestations with dm and not pm. Both are treatable with prednisone, immunosuppressants, ivig, etc but there is no effective treatment for ibm.
Ibm is a different disease and progresses very, very slowly over a period of years. The pattern of weakness is different as well.
Did your doctors test your cpk, sed rate, or other markers of inflammation? None of these are definitive but combined with your clinical symptoms your doctor can diagnose your disease. Most myositis patients have a biopsy as that is often the only way to definitively diagnose if and which myositis you have.
You might want to go to the community forums on www.myositis.org.
Here are some information sites for you:
http://www.mda.org/publications/fa-myosi-qa.html
http://www.merck.com/mmpe/sec04/ch032/ch032d.html
http://emedicine.medscape.com/article/1172746-overview
You need to make sure you find a rheumy or neurologist who is experienced treating auto immune diseases. Large, teaching hospitals and clinics like Johns Hopkins, Northwestern, Cleveland Clinic are usually the best bets.
Make a complete list of your symptoms even if you don't think they are relative and take all the previous lab tests to your new doctor. You might want to post on the myositis site and see if anyone can recommend a doctor or clinic near you.
I also post on that site (Bill Simeral) since I have lupus, scleroderma and pm. My case was extreme and life threatening but I survived and have come back (not all the way) from being a quadriplegic and not being able to swallow less than 5 years ago. Life if good again but it did a lot of damage. I have never heard of a more severe case and most are eventually treatable and muscle weakness treatable with physical therapy.
These are very rare diseases and NO ONE can tell you exactly how your case will progress or respond to treatment. Every case is unique and that is why it is so important to find an experienced doctor or team of doctors.
Good luck.
Bill