It is often difficult to diagnose myositis. Usually a specialist in autoimmune diseases, known as a rheumatologist, is required to establish the diagnosis.
The diagnosis of myositis is based on the careful analysis of many factors, including a thorough history and physical examination, which are essential. There are also certain laboratory studies that are helpful when considering the disease's diagnosis. It is important to note that the diagnosis cannot be made based on any specific blood test.
To help in the evaluation, it is often necessary to perform specific muscle testing. One such test is called an electromyogram (EMG). In an EMG test, surface electrodes measure the muscles' responses to small needle pricks. In addition to specific muscle testing, it may be necessary to perform a biopsy of the involved muscle to confirm the diagnosis of myositis.