Immune-mediated myositis
Immune-mediated myositis is a group of rare autoimmune muscle diseases where the body’s defense system mistakenly attacks its own muscle tissue, causing inflammation, weakness, and pain that can significantly affect daily life.
Table of contents
- What is immune-mediated myositis?
- Types of immune-mediated myositis
- Who gets immune-mediated myositis?
- Signs and symptoms
- What causes immune-mediated myositis?
- How is it diagnosed?
- Treatment and management
- Living with immune-mediated myositis
What is immune-mediated myositis?
Immune-mediated myositis, also called idiopathic inflammatory myopathy (idiopathic means the exact cause is unknown, and myopathy means a muscle disease), is a chronic disease marked by muscle inflammation[3][5]. In this condition, your immune system—which normally protects your body from infections—mistakenly attacks your own healthy muscle fibers and can injure or destroy them[5].
The muscle inflammation in myositis is caused by white blood cells of the immune system. These cells are normally supposed to protect the body from infections like bacteria and viruses. However, in people with myositis, these cells mistakenly attack healthy muscle tissue, which affects muscle function and can lead to fatigue and weakness[5].
Myositis can affect the whole body, not just the muscles. Some patients can have other symptoms such as joint problems, lung inflammation that causes coughing or shortness of breath, and skin inflammation or rashes[5].
Types of immune-mediated myositis
There are several different forms of immune-mediated myositis. Each type has different characteristics, affects different muscle groups, and may require different treatment approaches[3][5].
Polymyositis
Polymyositis affects multiple muscles at the same time. It usually causes symptoms in muscles on or near the center of your body, such as shoulders, hips, and thighs. Polymyositis develops gradually over time and typically affects adults. Women are twice as likely to develop polymyositis than men[5].
If you have polymyositis, you might have trouble performing movements you usually can, including standing up after sitting, climbing stairs, lifting objects, and reaching over your head[5].
Dermatomyositis
Dermatomyositis is a form of myositis that affects your skin in addition to your muscles[5]. It is characterized by distinctive skin changes along with muscle weakness. The rash often appears on the face, eyelids, knuckles, elbows, knees, chest, and back[14].
The average age of diagnosis is bimodal—meaning there are two peak times when people are diagnosed. Juvenile dermatomyositis is most commonly diagnosed between 4 and 14 years of age, while adult dermatomyositis is diagnosed between 40 and 60 years of age[7]. Dermatomyositis affects both genders with a two-to-one female-to-male ratio[7].
Inclusion body myositis
Inclusion body myositis is a degenerative muscle disease that usually affects people older than 50. It causes muscle weakness in your hands and your legs below your knees. It can also affect the muscles in your throat that help you swallow[5]. Men are affected about one-and-a-half to two times more often than women[5].
If you have inclusion body myositis, it might be hard to use your hands and fingers to do precise tasks like buttoning a shirt, grip something small, walk or stand, or swallow[5].
Immune-mediated necrotizing myopathy
Immune-mediated necrotizing myopathy (IMNM), also called necrotizing autoimmune myopathy, is characterized by severe muscle weakness in the muscles closest to the center of the body, usually with little effect on other parts of the body[2][6]. The condition involves necrosis, or cell death, in the muscles[2].
Onset is relatively quick, happening over days, weeks, or months, and usually occurs in adults between the ages of 40 and 60[2]. IMNM is characterized by highly elevated levels of a muscle enzyme called creatine kinase in the blood, severe muscle weakness, and muscle tissue that shows cell death with minimal inflammatory cells when examined under a microscope[3].
Antisynthetase syndrome
Antisynthetase syndrome is another form of myositis that often includes muscle inflammation, lung disease, joint inflammation, and specific skin changes[5].
Who gets immune-mediated 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[5].
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)[5].
Gender
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[5].
Ethnicity
People of predominantly Sub-Saharan African descent are three times more likely to get myositis than people with little or no such ancestry[5].
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[5]. The exact number of people affected by myositis is unknown, but estimates show about 50,000 in the US living with the disease[5].
Signs and symptoms
Symptoms of myositis include muscle inflammation, weakness, fatigue and, in some people, muscle pain. Each patient’s disease experience and mix of symptoms is unique. Some cases are very mild, while others are severe[5].
Muscle weakness
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[5]. 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[5].
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[5].
Sometimes, in the most severe cases, the muscles of the throat or diaphragm can weaken, leading to trouble swallowing or shortness of breath[5].
Symptoms specific to immune-mediated necrotizing myopathy
Those with necrotizing myopathy may experience weakness in the muscles closest to the center of the body, like the shoulders, forearms, hips, thighs, neck, and back. Common difficulties include climbing stairs and standing up from a chair, lifting arms over the head, falling and difficulty getting up from a fall, shortness of breath and chronic dry cough, and difficulty swallowing[2].
Skin and other symptoms
In dermatomyositis, characteristic skin changes appear along with muscle symptoms. Some patients can have other symptoms such as joint problems that resemble those in rheumatoid arthritis, lung inflammation that causes coughing or shortness of breath, and skin inflammation or rashes[5].
What causes immune-mediated myositis?
It is not clear why these conditions develop, or what sets it off for most people, though there are clues in some cases[5]. In most cases, the cause of an idiopathic inflammatory myopathy is unclear. For some reason, the body’s immune system turns against its own tissues in an autoimmune process[6].
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[5].
Risk factors for immune-mediated necrotizing myopathy
Causes of immune-mediated necrotizing myopathy can be associated with certain medications, especially statins used to manage cholesterol, specific autoantibodies (proteins made by the immune system) including anti-HMGCR and anti-SRP, cancer, viral infections, or other connective tissue diseases[20].
There are different categories of necrotizing myopathies characterized by distinct risk factors and disease course. These categories are mainly differentiated based on autoantibodies measured in the patient’s blood[2].
How is it diagnosed?
Since necrotizing myopathy is a rare disease, many physicians may not be familiar with the signs and symptoms. If you are struggling to find an accurate diagnosis, visiting a specialist can help[2].
Diagnosing typically starts with a detailed history, physician examination, breathing tests and imaging, such as a CT scan of the lungs. Blood tests are performed to measure markers of inflammation and muscle damage, and to check for the presence of autoantibodies. Additional tests such as muscle imaging, electromyography (a test that measures muscle electrical activity), or biopsies (taking small tissue samples) of the lung, muscle or skin might be needed[8].
A diagnosis of myositis-related disease should be based on the combination of the patient’s clinical profile, imaging results and results of autoantibodies. There is not one specific test that is relied on for the diagnosis—it’s a combination of several different things[8].
If you are experiencing muscle symptoms involving weakness or fatigue, talk to your doctor to begin the diagnosis process, which includes a muscle biopsy to detect cell death and various blood tests to detect the presence of autoantibodies[2].
Treatment and management
As with other types of myositis, there is no known cure for immune-mediated myositis. However, treatments are available that can successfully manage symptoms[2].
Immunosuppressive therapy
Though there is no cure for immune-mediated necrotizing myopathy, early and intensive treatment with drugs that suppress the immune system (immunosuppressive drugs) can sometimes help to manage the disease and avoid long-term disability[11].
Glucocorticoids, particularly prednisone, are often the first-line treatment. These medications help to reduce inflammation and swelling, and suppress damaging autoimmune responses. Long-term use of high-dose glucocorticoid therapy, however, may produce unwanted side effects, such as steroid myopathy (weakness from high dose steroids), decreased bone density, increased tissue swelling, and weight gain[11].
Therapy with other immunosuppressive drugs, such as azathioprine, methotrexate, mycophenolate mofetil, tacrolimus, or cyclosporine may be beneficial. Additional treatment options used alone or in combination may include intravenous immunoglobulin (IVIG) or the monoclonal antibody rituximab[11].
Treatment plans are typically individualized to meet the needs of the affected person and ongoing monitoring is required to optimize the treatment protocol[11].
Treatment approach based on disease subtype
Autoantibody status in immune-mediated necrotizing myopathy has considerable correlation with clinical characteristics, outlook, and recommended choice of immunosuppressive treatment. Patients with anti-HMGCR IMNM tend to respond well to intravenous immunoglobulin, and IVIG therapy alone may be sufficient treatment for certain patients. In anti-SRP IMNM, early rituximab is commonly favored[9].
Prompt initiation of aggressive treatment with immunosuppressive drugs is often indicated, as both anti-SRP and anti-HMGCR IMNM can potentially cause debilitating weakness, and muscle shrinkage and irreversible fatty replacement happen early in the disease course. Patients with IMNM frequently require combination therapy to achieve disease control, and have a high rate of relapse when tapering immunosuppression. Young age of onset is a poor prognostic factor[9].
Supportive care
Multidisciplinary care can improve the overall health of people living with immune-mediated myositis, and may include recommendations from a variety of specialists[11].
Physical therapy may be recommended to help improve muscle strength and avoid development of contractures (muscle shortening and tightening)[11]. A tailored exercise program can help maintain and improve muscle strength and flexibility. Physical therapists work with patients to create a safe and effective regimen[18].
Occupational therapists help patients adapt their daily activities and use assistive devices to maintain independence and quality of life. For patients experiencing difficulty swallowing or speaking, specialized therapy can help improve these functions[18].
A balanced diet rich in foods that help reduce inflammation can support overall health and well-being. A nutritionist can provide personalized dietary recommendations[18].
Living with immune-mediated myositis
Living with myositis requires adjustments and ongoing management. Life after diagnosis will likely be very different than what you’re used to. The first year is the hardest, but it’s important not to give up[15].
Self-care strategies
Conserve your energy by cutting corners where you can, at home and at work. Consider using helpful kitchen tools and appliances for easier meal preparation. Ask for help—consider using apps or community support to get others to assist with laundry, shopping, transportation to appointments, or bringing meals[15].
Keep moving as much as you can. Exercise is considered medicine for myositis. Start slowly and increase as tolerated. Ask for physical therapy or occupational therapy if you need help with moving and managing at home[15].
Managing information and medical care
Learn as much as you can from reliable sources. Consider getting a second opinion at a myositis specialty center, as myositis is a rare disease and many local doctors are not experts in treating it[15].
Create a medical binder where you collect all the information about your condition, including visit summaries, test results, and questions you have for your next visit. This information is also essential for family and doctors if you are unable to speak at some point. Keep printed records of abnormal tests[15].
Keep a list of all your medications, including those prescribed by non-myositis providers, over-the-counter drugs, and supplements. Also include drugs you did not tolerate and why, so providers do not try to prescribe them again[15].
Working with your healthcare team
The complexity of diagnosis and treatment is one reason multidisciplinary care is key. Specialists in pulmonology (lung medicine), rheumatology (autoimmune disease), neurology (nerve and muscle), dermatology (skin), and other areas may be involved in helping manage the disease[8].
Treatment can include a combination of steroids, drugs that suppress the immune system, medications that slow tissue scarring, pulmonary rehabilitation, or in severe cases, lung transplantation. The intensity of treatment depends on the disease severity and rate of progression[8].
It’s important to know that treatment is available and can be effective. Myositis-related disease often responds to treatment, especially when caught early[8].
