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Idiopathic inflammatory myopathies (IIM), commonly referred to as “myositis,” are chronic diseases marked by muscle inflammation. The exact number of people affected by myositis is unknown, but estimates show about 50,000 in the US living with the disease.

A middle-aged man getting physical therapy for the upper arm muscles.

What is myositis?

Myositis is an autoimmune disease characterized by inflammation of muscle. The disease can present in a variety of different forms, and people who have lupus, scleroderma or vasculitis may also have muscle inflammation as a secondary feature. Myositis can affect the whole body, not only the muscle.

What are the types of myositis?

Autoimmune inflammatory myopathies may be primary – occurring on their own – or secondary, occurring in patients who have other rheumatic diseases, such as, such as, scleroderma or vasculitis.

Different forms of primary myositis include:

What causes myositis?

The muscle inflammation in myositis is caused by white blood cells of the immune system, which are normally supposed to protect the body from infections. In people with myositis, however, these cells mistakenly attack a person’s own healthy muscle fibers and can injure or destroy muscle fibers. This affects muscle function and can lead to fatigue and weakness.

The white blood cells of the immune system generally protect us from things in the environment, like bacteria and viruses. In myositis, the immune system mistakenly injures muscles and other tissues, causing muscle weakness and other related conditions. It is not clear why these conditions develop, or what sets it off for most people, though there are clues in some cases.

Who gets myositis?

Although anyone can get myositis, there are numerous risk factors by age, sex, and ethnicity. People in their middle age, women, and those with Sub-Saharan African descent are at higher risk.


A peak incidence of idiopathic inflammatory myopathies takes place in people between the ages of 45 and 64 (about 8 to 10 new cases per 100,000 people per year). People in younger (25 to 44) or older (65+) age groups get myositis less often (about 3 to 5 new cases per 100,000 people per year).


Polymyositis and dermatomyositis affect women two to three times more than men, while inclusion body myositis affects men about one-and-a-half to two times more than women.


People of predominantly Sub-Saharan African descent are three times more likely to get myositis than people with little or no such ancestry. It is estimated that approximately 7,000 people are diagnosed with myositis every year, and there are upwards of 50,000 people in the United States who have it. There is no special geographic area where myositis is more common.

What are the symptoms of myositis?

Symptoms of myositis include muscle inflammation, weakness, fatigue and, in some people, muscle pain. But it can affect the whole body: Some patients can have other symptoms such as arthritis in the hands that resembles those in rheumatoid arthritis, lung inflammation that causes coughing or shortness of breath, and skin inflammation or rashes. Each patient’s disease experience and mix of symptoms is unique. Some cases are very mild, while others are severe.

Muscle weakness in myositis

The most common symptom of myositis is muscle weakness. The weakness often develops slowly, and can be subtle at first, influencing patients’ ability to do certain activities. They can have trouble doing tasks that require having their arms held above their head – things like washing, brushing, or blow drying their hair, reaching items on high shelves, or hanging up an overcoat can be hard. Additionally, they can have trouble getting up from low chairs, getting out of a car, or climbing steps. Patients can trip and be unable to catch themselves or be unable to get up from the floor after falling. Sometimes, in the most severe cases, the muscles of the throat or diaphragm can weaken, leading to trouble swallowing or shortness of breath.

In addition to impacts on muscle strength, muscle endurance can be affected, and patients often report significant fatigue and difficulty sustaining physical efforts. Muscle pain is not present in most cases, however, about a third of the time, significant muscle pain can be present.

Patients with inclusion body myositis have a slightly different pattern of weakness, and they may have more involvement of their hands – they may report dropping things or having difficulty carrying heavy items like bags of groceries or pots and pans.

Myositis symptoms in other parts of the body

There are many other possible symptoms, and these may even be the main feature of disease in some people, as opposed to muscle weakness. These include:

  • Inflammatory arthritis: Pain and swelling of joints, generally worse with inactivity and early in the morning, associated with prolonged stiffness. The arthritis can resemble or overlap with rheumatoid arthritis.
  • Interstitial lung disease: This is an inflammatory lung disease that causes cough and/or shortness of breath.
  • Rash: There are several characteristic rashes in dermatomyositis, often with a dark red or purple hue. These commonly are itchy, and can affect the scalp, around the eyes, the chest, and the hands.
  • Mechanic’s hands: This is a thickening of skin on the sides of the fingers, often associated with uncomfortable cracking/splitting of the skin.
  • Raynaud’s phenomenon: This is an abrupt, episodic decrease in blood flow to one or several fingers at a time, which presents with a visible change in skin color to blue or white. It typically occurs after exposure to cold and can be uncomfortable.
  • Nail bed/cuticle inflammation: There can be redness or pain along the nailbeds.

The particular mix of symptoms varies by patient, and since individual symptoms often mimic those of other conditions. This can make a diagnosis hard to pin down initially and a correct diagnosis may be delayed. It is important to note that there are other causes of muscle weakness and pain such as drug toxicities and viral infections, these possibilities must often be ruled out first.

How is myositis diagnosed?

Myositis can be hard to diagnose, but comprehensive assessment using all the tools available can make this possible. A diagnosis is made by taking the patient’s history, conducting a physical exam, and performing diagnostic tests, including. These may include blood tests, imaging exams (MRI and/or ultrasound), electromyography and nerve conduction studies, and biopsies of the muscle and/or skin.

Symptom history and physical exam

Patients with myositis usually complain of muscle weakness, particularly in the proximal muscle groups like the deltoids in the arms and the quadriceps in the upper legs. A doctor can often detect and quantify the degree of muscle weakness with a simple physical exam. It is important to note that there are other causes of muscle weakness and pain such as drug toxicities and viral infections, so these possibilities must be considered as well.

Blood tests for myositis

Diagnostic blood tests will usually show high levels of muscle enzymes in the circulation, which is a sign of muscle breakdown and damage. There are also some specific blood tests for autoantibodies that may be present in patients with inflammatory myopathies.

When cells are damaged, they leak out some proteins, which can be found in the blood. Different parts of the body have different proteins – when there is an infection or some other injury to one particular type of cell in the body, there can be a spike in the proteins from that particular cell in the blood.

The most common blood tests for muscle proteins are:

  • creatine kinase or creatine phosphokinase (CK or CPK)
  • aldolase
  • lactate dehydrogenase (LDH)
  • myoglobin

Anything that causes muscle injury, even vigorous exercise, can make the blood levels of these proteins go up. In most patients with myositis, the levels of these proteins go up when the disease is out of control and improve with treatment. However, some patients with severe disease only have slight increases in muscle proteins, and can even have normal levels, so the tests must be interpreted by a doctor in the context of all the patient’s signs and symptoms.

There are nonspecific indicators for inflammation, called the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). These studies are often elevated in myositis patients, but a significant number of patients never have any elevation in these markers, despite having active disease.

Blood markers (autoantibodies) in myositis

A very important advance for myositis has been the identification of markers of specific abnormal immune responses, called autoantibodies. These are found in many, but not all, myositis patients. Some autoantibodies have clear clinical associations, such as an increased risk of lung disease, arthritis, or cancer, and help guide the use of tests to monitor patients. The tests have been used to identify subgroups of patients with different sets of symptoms.

For example, ASyS is defined in part by patients testing positive for one of a set of autoantibodies against proteins called tRNA synthetases, such as anti-Jo-1, anti-PL-7, anti-PL-12, or anti-OJ. These patients can have muscle weakness, but also commonly have lung disease, arthritis, Raynaud’s phenomenon, and “mechanic’s hands” – thickening of the skin on the palm of the hands and fingers. Other tests, like anti-SRP and anti-HMGCR, are associated with necrotizing autoimmune myopathy (NAM), also known as immune-mediated necrotizing myopathy (IMNM), where the symptoms tend to be limited to the muscle, and the levels of muscle enzymes in blood are often very high.

In approximately 15% to 20% of cases of dermatomyositis, and less often in other forms of myositis, myositis occurs in the setting of cancer. For this reason, when any myositis patient is newly diagnosed, their physician should screen them for cancers. In that case, the dermatomyositis is believed to represent an effort by the immune system to eliminate the cancer, but because the cancer has some similar proteins to skin and muscle, that immune response causes injury to those other tissues as well. Some autoantibodies are seen more commonly in patients whose myositis is associated with cancer, such as anti-TIF-1γ and anti-NXP-2. Only about ¼ of patients with anti-TIF-1γ and anti-NXP-2 will also have cancer. Nonetheless, the autoantibody test helps identify which patients should have more cancer screening than others.

Myositis autoantibodies can also be useful in patients whose symptoms are in the early stages, not fully defined, or when the main initial symptom is something other than muscle weakness, like lung disease. When a myositis autoantibody is present, it can shine a light on the underlying condition, and lead to a faster diagnosis.

Additional tests: Imaging, electromyography and biopsies

Additional tests to confirm the diagnosis include electrodiagnostics, biopsies and radiological imaging.

Your doctor may order an ultrasound or MRI to look for evidence of inflammation in the muscle. When muscle is injured, the muscle swells up slightly and holds on to water. This pattern of muscle swelling can be seen with an MRI. When such pattern is demonstrated on an MRI, this is another sign that myositis may be present.

Electrodiagnostics are specialized tests done performed by neurologists to examine the function of nerves, muscles, and the ability of nerves to communicate with muscles using small electrical signals. An electrodiagnostic test called an electromyograph (EMG test) can provide information about muscle injury can detect the specific pattern of changes that develop in muscle tissue in a person who has myositis. It is often performed in conjunction with a nerve conduction study (NCS), which sends electrical signals to specific nerves. The NCS measures the strength of and speed with which the pulses travel through the nerve to determine whether they are damaged.

A muscle biopsy is the gold standard to diagnosis myositis. It can demonstrate inflammatory changes in the muscle tissue – that is, cellular- and molecular-level evidence of muscle damage caused by the immune system. It can also rule out other causes of injury to the muscle. Similarly, a skin biopsy is helpful to determine whether a person has dermatomyositis.

How is a diagnosis of polymyositis versus dermatomyositis made?

This can be difficult, as both types of myositis can look like other diseases. A muscle biopsy is a common method to diagnose the condition. In people with dermatomyositis, there may be more skin involvement, such as a rash, and a skin biopsy can be done. Blood tests, magnetic resonance imaging (MRI), and other specialized neurologic tests, such as EMG testing, can be helpful as well.

(Find a doctor at HSS who treats myositis.)

What is the treatment for myositis?

There is no cure for myositis, but most patients can manage their symptoms. It can be a frustrating, mysterious disease, but there are many treatments and social services available to those who live with this oft-misunderstood condition. Treatment of myositis should always include regular exercise and physical therapy, but may also include immunosuppressive medications like steroids, methotrexate, azathioprine, or mycophenolate. Intravenous infusions of immune globulin or rituximab can be used in some cases. New and promising medications are being studied in clinical trials.

The pace of research in this area continues to accelerate, hopefully leading to more therapies and better outcomes for myositis patients.

Exercise and physical therapy for myositis

It is somewhat counterintuitive to recommend exercise to myositis patients, whose muscle is already injured by their immune system. However, recent research has shown that physical therapy can help maintain and improve muscle function in myositis patients, without significant risk of harm. Physical therapy is especially important in inclusion body myositis, since patients with this form of myositis do not generally respond well to medicines used in the other forms of myositis. Of course, every patient’s situation is unique, and their personal course of therapy should be discussed with a physician before starting. There is no specific diet or food that is proven to help with myositis, but a healthy diet is important for general well-being, and especially in people who have a chronic illness.

Myositis medications

The medicines used to treat myositis most often work by blocking or suppressing the white blood cells of the immune system, since these are causing the underlying damage to muscle tissue. This is helpful for controlling the disease, but it also can affect the normal functioning of the immune system and requires careful monitoring by a physician.

Steroids, like prednisone, are the most common treatment. They work very quickly and can be very effective but have many side effects that can build the longer patients are on treatment, especially with high doses. Since myositis treatment is mostly long-term, there is a need for additional medications for “steroid sparing,” to allow for less use of steroids, or to use in place of steroids.

While immunosuppressive medications like methotrexate or azathioprine are not approved by the FDA for use in myositis, they have been frequently incorporated into treatment of myositis for many years. If additional agents are required, mycophenolate mofetil, intravenous immune globulin (IVIG), tacrolimus, hydroxychloroquine, or rituximab have all been used and can be helpful. IVIG was recently shown in a large clinical trial to improve disease control in dermatomyositis patients who have not achieved disease control with steroids and other medicines alone and is now formally FDA-approved for treatment of this condition. Unfortunately, physicians treating the disease do not currently know up front which patients are most likely to tolerate one medicine versus another, or experience side effects, so patients may have to try several medicines to find the right mix.

Regardless of the specific treatment employed in most cases of myositis, substantial improvement can and should be seen. This can be rapid, in some cases manifesting over a period of weeks to months. A lack of response to therapy, or need for ongoing high doses of steroids, should prompt consideration of other medicines, combinations of medicines, or re-evaluation of the diagnosis.

An exception to this is that immunosuppressive therapy does not work well in inclusion body myositis, and so the risks of therapy do not exceed the benefits in most patients. Choosing the right therapy is a complex decision and must be done by a patient in conjunction with their doctor after discussing the risks and benefits of each option.

There are several clinical trials for myositis patients that are evaluating different, promising medicines in these diseases. Hopefully, this will lead to more options for patients who continue to struggle with the conventional medicines currently available. Visit the HSS Scleroderma, Vasculitis & Myositis Center of Excellence to learn more about myositis clinical trials.

What are some signs and symptoms of a myositis flare?

There are many signs and symptoms of a flare for myositis patients. The most common is muscle weakness. Others include:

  • fatigue, fevers or weight loss
  • blood test results showing increased muscle enzymes like creatine kinase (CK)
  • new or worsening rashes in patients with dermatomyositis
  • shortness of breath or cough in myositis patients with lung involvement
  • arthritis (pain or swelling in the hands)

Are there flare “patterns” in myositis?

Yes. It is estimated that 15% of people with myositis may experience only one flare. A larger group experiences flares that are separated by periods of complete inactivity of their disease. The largest group, however, experiences flares, separated by periods of relatively mild disease activity.

How does someone with myositis know if they are losing muscle strength?

This can be difficult to assess, but patients can notice more difficulty with day-to-day tasks, like exercising, climbing stairs, getting up from chairs, lifting things, or washing their hair. A physical exam by the doctor can be helpful. Blood tests such as creatine kinase (CK) levels can reveal muscle damage.

What happens if myositis goes untreated?

If left untreated, the muscle inflammation in myositis can lead to permanent muscle damage and loss of muscle mass. Myositis can be associated with problems in other organs like the joints and the lungs. In dermatomyositis, there is usually a rash or skin inflammation in addition to the muscle inflammation.

Myositis care at Hospital for Special Surgery

Hospital for Special Surgery provides exceptional clinical care and social support for people with myositis. Care is provided by our world-class Division of Rheumatology (ranked #2 in the United States by U.S.News & World Report) and the Scleroderma, Vasculitis & Myositis Center of Excellence. In addition, our Myositis Education and Support Program gives patients the opportunity to communicate with one another as well as with HSS and guest clinicians, social workers and other experts. Many of the articles below are adapted from presentations given to this group.

Video: Three HSS myositis patients share their experiences

Learn more about myositis from the content below or find a doctor at HSS who treats myositis.

Myositis overview articles

Myositis treatment articles

Myositis tips and calculators

More content from the HSS myositis support program

Myositis Patient Stories


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Reviewed and updated by David R. Fernandez, MD

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