How is the condition diagnosed?
Polymyositis is often suspected after a history and physical exam are done. Blood tests are commonly done to help make the diagnosis. When a person has this condition, the immune system often makes certain antibodies. These can be measured with a test called an antibody titer. Certain muscle proteins often increase in the blood due to muscle damage. For example, creatine phosphokinase and aldolase levels commonly rise. Another blood test, called an erythrocyte sedimentation rate, is also usually abnormal.
When these blood tests are abnormal, two other tests are commonly done to confirm the diagnosis:
Electromyography (EMG) involves attaching wires to the skin and measuring the electrical activity in the muscles. The response of the muscles to small shocks is also measured.
A muscle biopsy involves using a special tool to remove a small piece of muscle. The muscle tissue can then be sent to the lab for examination and testing.