What is myositis?

Myositis (my-o-SY-tis) is a rare type of autoimmune disease that inflames and weakens muscle fibers. Autoimmune diseases occur when the body's own immune system attacks itself. In the case of myositis, the immune system attacks healthy muscle tissue, which results in inflammation, swelling, pain, and eventual weakness. When there is no skin involvement, it is called polymyositis. When there is skin involvement, it is called dermatomyositis.

The areas of the body affected by myositis may differ from patient to patient. Most often, myositis involves the muscles in the upper arms and thighs, which can cause difficulty raising arms above the head and rising from a chair. Some people may also experience symptoms in their lungs, such as difficulty breathing, while others may have difficulty swallowing. Women are more than twice as likely to be diagnosed as men, with most patients between ages of 30 and 60 when first diagnosed. In patients younger than 20 years old, the disease is referred to as juvenile myositis and may be treated differently.

Over time, myositis symptoms may continue to worsen until everyday tasks, like climbing stairs or carrying groceries, become difficult. These symptoms develop gradually and though there is no cure, treatments are available to retain muscle strength and function. It is important to work with your rheumatologist to delay myositis complications as long as possible. Depending on whether your lungs or esophagus are affected, you may experience some of the following symptoms or physical findings:

  • Breathing difficulty ranges from shortness of breath to respiratory failure.
  • Rashes may develop over the knuckles, around the fingernails, around the nose and cheeks, and on the chest, in addition to other areas. In the presence of a typical myositis related rash, the diagnosis is referred to as dermatomyositis. Skin involvement can sometimes be quite severe.
  • Calcinosis means that over time, calcium deposits form in your muscles, skin, and connective tissues which can be painful and lead to infections.
  • Swallowing difficulty including weight loss and malnutrition or aspirating food or liquids into your lungs can lead to pneumonia.

Myositis frequently occurs with other conditions, which share similar symptoms or affected organs. For example, people with myositis may have other autoimmune conditions like lupus or rheumatoid arthritis. They can also experience Raynaud's disease (this is a blanching of the fingers when exposed to the cold). Depending on how long the myositis symptoms have occurred and which muscles are affected, heart muscle or lung tissue can also become inflamed, leading to poor health consequences like heart arrhythmias and interstitial lung disease.

What causes myositis?

The specific causes of myositis are unknown. There are characteristics in common with other autoimmune disorders that may help researchers determine specific causes. Research has identified some causal pathways, including:

Virus Trigger: Some patients have been exposed to a virus like HTLV-1 or the Coxsackie B virus prior to developing myositis symptoms. This does not mean that either virus causes the disease; the patient was likely to develop an autoimmune disorder anyway, but and the virus may have been the trigger that initiated the symptoms.

Drug Trigger: Some patients with myositis were exposed to drugs such as penicillamine, interferon-alpha, cimetidine, carbimazole, phenytoin, growth hormone, and hepatitis B vaccine. These drugs treat a range of conditions from ulcers to cancer and do not otherwise have anything in common. Whether they truly cause myositis remains unclear.

Genetic Trigger: The specific genes that put a person at risk for myositis have not been identified, but there may be genetic factors that increase the likelihood in some patients for myositis to occur. There is also on-going research into the blood mixing between mother and fetus that could possibly create risk for myositis in either the mother or child later in life.


What are the symptoms of myositis?

You should contact your physician if you experience unexplainable weakness in the muscles closest to the middle of your body (such as your thighs, hips, shoulders, neck, back, or forearms). Specific symptoms include:

  • Gradual, worsening weakness that develops over a period of weeks or months
  • Difficulty rising from a seated position or reaching above your head
  • Difficulty swallowing
  • Joint pain
  • General, unexplained fatigue

How is myositis diagnosed?

A myositis diagnosis involves multiple tests. Your physician will ask you questions about your muscle weakness symptoms. It is worthwhile to take a moment before your appointment and write down when you first noticed your symptoms. Do you notice anything that makes it worse (or better)? Do any of your immediate family members have an autoimmune disease? Your doctor will also ask you for a detailed description of your past medical history and any conditions you currently have or treatments that are in process.

If your physician suspects that your muscle weakness may be myositis, he or she may order tests that could include:

  • Blood test: to determine whether you have elevated muscle enzymes such as creatine kinase (CK) and aldolase, which can indicate muscle damage. Blood tests also indicate specific autoantibodies which are associated with polymyositis. If these autoantibodies are found in your blood, they will help determine which subtype of myositis you have.
  • Electromyography: a test to measure electrical activity in muscles
  • Muscle biopsy: used to look for damage, infection, inflammation, or abnormal changes

How is myositis treated?

There is no cure for myositis, but there are a number of different treatments that improve your muscle strength and function. Starting treatment as soon as you first discover symptoms can minimize the complications you experience and slow or stop the course of the disease. Your rheumatologist will help determine the best treatment or treatment strategy:


Depending on the type and severity of your symptoms, your doctor may prescribe the following therapies:

  • Physical therapy: Strength training exercises help maintain strength and improve flexibility.
  • Speech therapy: Myositis can weaken muscles around your vocal chords and impact speech; a speech therapist can help.
  • Diet changes: Myositis can affect the esophagus as well as jaw muscles. Registered dieticians can advise you on which foods provide the most nutrition with the least difficulty chewing and swallowing.
  • Emotional support: An autoimmune disease support group or counseling can support you and your emotional needs as you manage your health.


Myositis treatments include prescription and over-the-counter medications, such as anti-inflammatories, steroids, and other immunosuppressants.

Other Treatments

After trying other therapies, your rheumatologist may recommend intravenous immunoglobulin (IVIg), an IV treatment that contains healthy antibodies collected from thousands of blood donors. It is an expensive treatment that needs to be repeated regularly to maintain its effects and block the myositis muscle damage from occurring. Another potential treatment is rituximab, an antibody that depletes B cells, which make the antibodies that damage muscles. Clinical trials of other agents are currently in progress.