Diagnosis Make an Appointment Refer a Patient Ask a Question Reviewed by Liudmila Kastsianok, MD, RhMSUS (October 01, 2018) How is Myositis Diagnosed? Often times it is difficult to diagnose myositis. Most often, 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. A thorough history and physical examination are essential for the diagnosis. There are certain laboratory studies that are helpful when considering the diagnosis of myositis. It is important to know 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, or EMG for short. The EMG involves testing of specific muscle groups. In an EMG test, surface electrodes measure the muscles responses to small needle pricks. A magnetic resonance imaging (MRI) scan of the muscles can be helpful in demonstrating inflammation in the muscles. In addition to specific muscle testing, it may be necessary to perform a biopsy of the involved muscle to confirm the diagnosis of myositis. Symptoms Treatment Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.