What are the other types of myositis?
Post-infectious reactive myositis can occur after some viral infections. After killing the virus, your immune system may cause inflammation in some parts of your body for a few months. If the inflammation occurs in muscles, it causes myositis.
The symptoms are similar to those of polymyositis (muscle pain and weakness) and you may get positive results in some of the test used for polymyositis. But post-infectious reactive myositis is usually mild and settles without treatment. If you have this you may also get positive results for some tests that diagnose polymyositis.
Inclusion body myositis (IBM) causes muscle weakness. Tests to diagnose IBM show similar results as tests for polymyositis and dermatomyositis. In IBM the weakness usually affects muscles in your hands, forearms or calves.
The key difference in IBM is the abnormal lumps of protein (inclusion bodies) found in muscle cells. These lumps are so tiny that they can only be seen with special microscopes.
IBM doesn’t respond well to steroids, so if you’re diagnosed with polymyositis and steroids aren’t working you may need further tests for IBM.
IBM only rarely causes muscle pain and it generally affects people over 50.