Polymyositis is usually accompanied with significant muscle weakness. Symptoms are difficulty getting out of chairs/off the toilet, raising your hands over your head, general fatigue, and/or swallowing difficulties. Doctors usually measure your sed rate as a sign of general inflammation and your cpk numbers which indicate muscle breakdown. PM usually hits the proximal muscles the hardest. Those are the muscles around your hip and shoulder girdles.
As with lupus diagnosis is often difficult and elusive. Further diagnostic tests include emg, mri, and usually a muscle biopsy. chronic myopathy is not a disease but a generic term and myositis diseases are some of the inflammatory muscle diseases under that category.
PM can vary from mild to extreme and onset can be fairly sudden to drawn out. There is no real consistent pattern. My case was very extreme and I lost 40 lbs of muscle mass in a week and was left a quadriplegic who could not swallow. My docs found a treatment (ivig) that worked (I was resistant to prednisone) but i have gone through 2.5 years of physical, occupational and speech therapies as well as working out on my own for the past 2 years. While not 100% I have returned to an active life but still have significant muscle weakness and fatigue.
Most cases are not like mine (not as extreme or as sudden) and there are many other causes of muscle problems. Lupus itself can cause similar symptoms and weakness.
PM attacks the muscle cells directly and dermatomyositis attacks the capilaries feeding muscle cells. DM tends to have skin rashes. Both can exhibit similar symptoms otherwise.
There is a third type of myositis called inclusion body myositis. There is debate whether this is really related to pm/dm or if it is an entirely different disease. It is very slow to develop and is not treatable at this time.
Here are links to more information on myositis diseases.
Hope this helps. You have a whole list of problems that could be part of a connective tissue disease like I have...mixed connective tissue disease. MCTD is a specific diagnosis but undifferentiated connective tissue disease (UCTD) is diagnosed when symptoms and tests are not conclusive to diagnose anything more specific. Frustrating but quite common.
Mixed connective tissue disease (systemic lupus, scleroderma, polymyositis), Raynauds phenomena, Hypertension, Barrett's esophagus.
Meds: prednisone 5mg, 50mg imuran, Lotrel 40/5mg, maxide 37.5/25mg, folic acid, potassium, aciphex 20mg, multi vitamins.
Maintain your optimism and you can beat the odds.
"Although the world is full of suffering, it is also full of the overcoming of it." Helen Keller