This information has been compiled for people affected by polymyositis. It provides general information to help you understand how you may be affected and what you can do to manage the condition. It also tells you where to find further information and advice from a polymyositis specialist Brisbane that you can trust.

What is Polymyositis?

Polymyositis belongs to a group of diseases known as the autoimmune muscle diseases. These are diseases where the body's protective immune cells make "a mistake" and attack healthy muscle tissue. There are quite a few different types. There's polymyositis, dermatomyositis, Inclusion Body Myositis, Necrotising Autoimmune Myositis (also known as NAM), juvenile myositis and myositis associated with other autoimmune diseases, including mixed connective tissue disease.

Myositis is a rare disorder. We only see a few dozen cases each year, even in the busy rheumatology clinic that we run at arthritisCARE in Brisbane.

Image of a male patient lying down on his back while being examined for leg muscle weakness
What are the symptoms?

The most common symptom of polymyositis, dermatomyositis, Inclusion Body Myositis and Necrotising Myopathy is weakness of the muscles. This symptom can sometimes feel like a bad virus with people finding it hard to get up out of bed or stand from their chairs, move around and climb stairs. Sometimes the muscles ache, but pain is not a big feature initially.

Other targets for auto-immune muscle diseases include the skin.  Rashes are quite common, particularly in dermatomyositis. These rashes can look like unusual sunburn on the chest and a purplish sort of area on the face, with red thick raised areas on the skin sometimes appearing over the knuckles or on the person's hands. Sometimes the lungs are also targeted. This is called interstitial lung disease and is quite a serious complication.

What causes it?

It's not certain what causes polymyositis, but many of the conditions are associated with the presence of autoantibodies and some are triggered by chemicals. One such chemical trigger is the group of drugs called statins (often prescribed to lower cholesterol levels). Very rarely, statins can cause a condition called Necrotising Autoimmune Myopathy (NAM). It is uncommon, but approximately one in every 100,000 patients on a statin might experience this condition.

There are many autoantibodies associated with myositis and these can be investigated through tests that your Rheumatologist can organise for you. Some of these autoantibodies target specific enzymes within the DNA and RNA of the person's cells. These are sometimes referred to as antisynthetase antibodies. There are many other autoantibodies as well, which will sometimes give a clue to the existence of an autoimmune muscle disease like myosotis.

How is it diagnosed?

Polymyositis and the autoimmune muscle diseases can be hard to diagnose initially. Apart from the symptoms of weakness and tiredness, the test that will most likely suggest there is a muscle disease problem is an elevated level of the enzyme called the creatine kinase (CK) in the blood.

This is an enzyme produced by normal muscle function in a range of about 50 to 200 units. However, when the muscles are being attacked by the immune system, the CK level might rise up to 5,000 or 10,000 units. Finding evidence of this very high level of CK will sometimes be the clue that your doctor needs to start the process of further investigating the presence of myositis and formulating a treatment plan for you.

Other conditions can also give you a high CK, including things like thyroid disease; toxins like alcohol and other drugs; acute dehydration; acute fever and illness. With many of these however, the elevated CK level will return to normal once the cause is removed. But with an autoimmune muscle disease like polymyositis, the CK level stays elevated unless it is actually treated.

Other blood tests will sometimes provide clues to the existence of myositis, including tests for autoantibodies and muscle-specific antibodies. The most well-known ones being the antisynthetase antibodies.

An electrical test called an EMG can sometimes show abnormalities of the muscles. And an MRI is often done on arms or legs to investigate muscle injury or muscle oedema (or swelling). An abnormal MRI will identify any area of muscle that is affected. This affected area can then be targeted by a surgeon to get an accurate muscle biopsy. So a muscle biopsy is probably the definitive test for diagnosing polymyositis. Although, if the characteristic rash, symptoms, elevated CK and auto-antibodies are all present and confirming an autoimmune muscle disease, a muscle biopsy is not always required.

How is it treated?

All of these conditions are treatable. Some respond very well to treatment, with others being less responsive. Polymyositis, dermatomyositis, myositis associated with other autoimmune diseases and those triggered off by statins respond well to immunosuppressive drugs like prednisone, steroids and other disease-modifying drugs like azathioprine, mycophenolate, methotrexate and hydroxychloroquine.

For severe disease, particularly if the lungs are involved, other drugs including cyclophosphamide and rituximab may need to be used. Sometimes intravenous immunoglobulin is also used to turn off the disease.

Image from a muscle biopsy showing evidence of polymyositis

Muscle biopsy showing polymyositis

Most cases of polymyositis, including dermatomyositis and necrotising myopathy, can be very successfully treated and patients can go into remission, making a full recovery and go back to having a normal life, including even going back to playing sport. They may, however, need to remain in treatment for several years.

Inclusion Body Myositis is a bit trickier to manage. Medications available to Rheumatologists at present just slow the disease down, but there are trials in progress now exploring better options for management of this condition. It is a much slower form of autoimmune muscle disorder, so many patients have lived with the condition for over 20 years.

Just to complicate things, the genes that make people prone to polymyositis may also make them prone to certain forms of cancer. As a result, most adults with polymyositis and dermatomyositis undergo fairly comprehensive screening tests looking for relatively common forms of cancer like breast cancer, ovarian cancer, bowel cancer, etc.

The rate of cancer in polymyositis and dermatomyositis ranges from about 10 to 15% of patients and these cases can occur some years after diagnosis. Sometimes the cancer seems linked to the activity of the myositis and if the cancer is treated effectively, the myositis will then melt away. But this only applies to a small group of patients and most patients don't develop cancer at all and are treated successfully with conventional immune therapy similar to that used in the treatment of rheumatoid arthritis and lupus etc.

What can I do to help myself?

Seek advice from a Rheumatologist. Any person who feels incredibly weak in their muscles and feels like some acute process is affecting their muscle strength should talk to their doctor about a full examination and perhaps having a blood test for levels of creatine kinase (CK). This will help clarify very quickly whether or not there are any concerns regarding muscle health.  There are many other conditions that cause muscle weakness but myositis is relatively easy to diagnose.

Learn more and gain support for your myositis. Explore the resources, support and networking opportunities for myositis patients and their families available through the Myositis Association Australia.

Recommended further advice is available from:

The Myositis Association Australia website
https://myositis.org.au

Polymyositis Information page
https://myositis.org.au/polymyositis-info/

Dermatomyositis Information Page
https://myositis.org.au/dermatomyositis-info/

Necrotising Myositis (NAM) Information page
http://myositis.org.au/wp-content/uploads/2017/07/Necrotising-Myositis.-2017docx.pdf

Inclusion Body Myositis (IBM) information page
https://myositis.org.au/inclusion-body-myosit-info/

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