Inflammatory myopathies (muscle disorders) are chronic diseases primarily marked by muscle inflammation and weakness. The most common form of this disease is myositis.

What is myositis?

Myositis means inflammation of the muscles, regardless of the underlying cause. However, the term “myositis” is frequently used as shorthand to refer to common causes of inflammatory muscle disorders or idiopathic inflammatory myopathies.

What causes myositis?

There are many causes of muscle inflammation, including infections, drug or medication side effects, trauma, cancer and, especially. autoimmune disease, in which the immune system mistakenly injures muscle tissue, causing muscle weakness and other related conditions.

In autoimmune-related myositis, the muscle inflammation is caused by white blood cells called lymphocytes, which are normally supposed to protect the body from infections. In people with inflammatory myopathies such as myositis, however, these lymphocytes infiltrate and attack a person’s own healthy muscle fibers as well as foreign infectious bodies. After a period of inflammation, muscle fibers are destroyed. This affects the functionality of muscle tissue and leads to fatigue and immobility.

It is not clear why autoimmune conditions develop, or what triggers them in most people, although there are clues in some cases.

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, scleroderma or vasculitis.

Different forms of primary myositis include:

• polymyositis
• dermatomyositis
• inclusion body myositis
• autoimmune necrotizing myopathy

Who gets myositis?

Although anyone can get myositis, there are numerous risk factors by age, sex and ethnicity.

People with African descent are three times more likely to get it than those whose ancestry is predominantly from other racial or ethnic groups. Polymyositis and dermatomyositis affect women 2 to 3 times more than men, while inclusion body myositis affects men about 1.5 to 2 times more than women.

Regarding age, 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).

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?

The most common symptom of myositis is muscle weakness. The weakness often develops slowly and can be subtle at first. The symptoms of weakness depend on the group of muscles affected – most often, myositis affects the muscles closest to the trunk, at the shoulders and hips. The weakness in myositis is generally not associated with pain, but some muscle pain can be seen in about a third of patients. It can be hard to distinguish fatigue from weakness, and the two often go together.

People often notice difficulty with certain tasks. When the arms are affected, people can have trouble washing, brushing, or blow drying their hair, reaching things on high shelves, or hanging up an overcoat. When their legs are affected, they can have trouble getting up from a low chair, getting out of a car, or climbing steps. Patients may trip and then be unable to catch themselves before falling. Sometimes, in severe cases, the muscles of the throat or diaphragm can weaken, leading to trouble swallowing or shortness of breath.

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.

Beyond weakness, there are many other symptoms and comorbidities that can occur in people with myositis. For some patients, one or more of these may even be the main symptom or consequence of their disease. 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: Inflammatory lung disease, leading to cough 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: An abrupt, episodic decrease in blood flow to one, several or many fingers at a time, associated with a 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 can be very different from person to person and can make the diagnosis hard to pin down initially.

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 tests results showing increased muscle enzymes like creatine kinase (CK)
• shortness of breath or cough in myositis patients with lung involvement
• new or worsening rash in patients with dermatomyositis

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 is myositis diagnosed?

Myositis is a disease that can present in a variety of different forms and can affect the whole body – not only the muscle. This can make it hard to diagnose, but comprehensive assessment using all the tools available can make this possible.

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.

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.

Your doctor may order an MRI or ultrasound to look for evidence of inflammation in the muscle. Another test called an electromyograph (EMG) can provide information about muscle injury. The gold standard to diagnosis myositis is to perform a muscle biopsy which can demonstrate inflammatory changes in the muscle tissue.

Blood markers

A very important advance for myositis has been the identification of blood markers, called antibodies, which appear only in myositis. There are many of these markers that have been identified, and the list continues to grow. Some markers have clear clinical associations, such as an increased risk of lung disease or arthritis. They can reveal subgroups of patients with similar symptoms, and potentially help doctors and researchers understand the differences between those patients better.

They can also be useful in patients whose symptoms are in the early stages, not neatly defined, or when the main initial symptom is something other than muscle weakness, like lung disease. When present, these tests can shine a light on the underlying condition, and lead to a faster diagnosis. While it is not fully clear if, or how, these can guide treatment at this point, there are some signs that they may be helpful soon.

Other diagnostic tests

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

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. There is a pattern of changes that develop when patients have myositis, so seeing this pattern can help confirm the diagnosis in a patient who has weakness.

Biopsies: A muscle biopsy can show cellular and molecular evidence of muscle damage by the immune system, or rule out other causes of muscle injury, and is an important part of confirming the diagnosis of myositis. In patients with dermatomyositis, a skin biopsy can help as well, for similar reasons.

Ultrasound or magnetic resonance imaging (MRI) can be helpful to look at muscle in a less invasive fashion. 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 that pattern is evident, that is another sign that myositis may be present.

How is a diagnosis of polymyositis versus dermatomyositis made?

This can be difficult, as both types of myositis can look like other diseases. A biopsy is usually the most reliable method to diagnose. In people with dermatomyositis, there may be more skin involvement, such as a rash.

What are the effects of myositis?

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.

What is the treatment for myositis?

While there is no cure for myositis, there are a variety of treatments that can help patients manage their symptoms successfully. Polymyositis and dermatomyositis are treated with medications to suppress the immune system in order to stop inflammation. Treatment for any form of myositis, however, should always include regular exercise and physical therapy. Exercise may seem counterintuitive to recommend to someone whose muscle is already injured by their immune system but 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 medicines used in other forms of myositis generally do not work well. Of course, every patient’s situation is unique, and their personal course of therapy should be discussed with a physician before starting.

No specific diet or food has been proven to help with myositis, but a healthy diet is important for general well-being, and in particular in patients with a chronic illness.

Medication for myositis

Polymyositis and dermatomyositis are treated with medications that suppress the immune system in order to halt inflammation. Corticosteroids, like prednisone, are often prescribed at first because they can act quickly to quell the inflammation. Depending on symptoms, disease severity, and other organs involved, additional immunosuppressive medications either in pill or intravenous form may be recommended. Physical therapy or a structured exercise program can be very helpful too in order to regain muscle strength.

The medicines used to treat myositis most often work by blocking the white blood cells of the immune system in some way, since these are causing the underlying damage to muscle tissue. Steroids, like prednisone, are the most common treatment. They work very quickly and can be very effective but have a number of side effects that accumulate 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, tacrolimus, or rituximab have all been used. Importantly, 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.