What defining difference exists between polymyositis and inclusion body myositis?

Different diseases: Both are muscle diseases that are difficult to treat, polymyositis tending to affect shoulders and hips, inclusion body mysoitis the forearms. Polymyositis is the more treatable, but the more likely to become very serious, we know something of its cause unlike inclusion body myositis. Under the microscope they look different. Both are difficult and i wish you good luck and courage.