Diagnosing any disease is a bit like solving a mystery. The physician will collect a variety of information and fit this all together to form an understanding about what is causing your symptoms. For those with myositis, this process can be challenging for a number of reasons.
- Myositis diseases are rare, which means that clinicians may not be immediately aware of what to look for.
- Myositis often starts out looking like a number of different autoimmune diseases.
- Myositis takes a number of different forms, each of which is also very diverse.
- Myositis can occur in combination with other overlapping autoimmune diseases.
- Myositis symptoms are different in every patient.
The first step in any diagnosis is a medical history. The doctor will ask questions about your health in general, including detailed personal and family health histories. Then they will want to know about your symptoms: when you first saw signs of the skin rash, what made you first notice muscle weakness, whether you did anything to treat these symptoms yourself, whether there are certain things (foods, activities, weather) that make the symptoms better or worse, whether you had an infection or other illness around the time the symptoms started.
The next step will be a physical examination. The doctor will examine your skin symptoms and test your muscle strength. They may ask you to demonstrate activities that are difficult because of the weakness, such as walking up steps, lifting your arms over your head, squeezing something with your hands.
The history and physical will give the doctor some idea about a diagnosis. They may then use one or more of the following tests to help confirm a specific diagnosis:
Blood tests, especially the levels of certain muscle enzymes in the blood, can offer important clues, not only about what may be causing symptoms. However, muscle enzymes can be normal even when there is muscle involvement.
Diagnostic tests are typically ordered after blood tests are done to gather additional information. These tests may include a magnetic resonance imaging (MRI) scan and/or an electromyogram (EMG) and nerve conduction velocity (NCV) studies.
Muscle and skin biopsy are often the most definitive way to diagnose myositis diseases. Small samples of muscle tissue show abnormalities in muscles, including inflammation, damage, and abnormal proteins. For those with skin symptoms, doctors often biopsy a bit of skin to examine for characteristic abnormalities. A biopsy of muscle may not be necessary if the skin biopsy shows changes of dermatomyositis in the context of typical skin findings.
Other diagnostic tests may be done to further clarify the diagnosis or to rule out another disease or condition that has symptoms similar to myositis. In addition, it is recommended that doctors routinely screen newly diagnosed patients for cancer or lung disease (see complications). If you have questions about any of these tests, be sure to talk with your doctor or lab technician.
Questioning your diagnosis. Many myositis patients are diagnosed only after visiting many health professionals. If you or your physician believe your disease is not progressing or responding as expected, the next step may be a consultation with another physician, especially one who specializes in myositis.
Our Find a Doctor tool can help you find a list of health care professionals who have a special interest in myositis. The members of TMA’s Medical Advisory Board are also available to consult with your local physician.
Revised April 2025 by Victoria Werth, MD – dermatologist, research scientist, and TMA medical advisor
Disclaimer: Information provided on this website is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with any questions you may have regarding a medical condition.