Dermatomyositis (DM) is a condition in which inflammation causes muscle weakness and a distinctive rash. The symptoms are very variable and can range from mild to severe. Generally speaking, DM responds to treatment with medications such as steroids. DM can affect individuals at any age and usually is not inherited. DM which occurs in childhood – juvenile dermatomyositis – is covered in a separate factsheet.
DM belongs to the group of conditions called inflammatory myopathies (also sometimes called myositis). Another inflammatory myopathy called polymyositis is similar to DM but the skin rash is absent.
In this factsheet:
- Who gets dermatomyositis?
- What are the symptoms?
- What causes dermatomyositis?
- How is dermatomyositis diagnosed?
- How is it treated?
- What research is being done?
- Further information
Who gets dermatomyositis?
In adults, dermatomyositis usually occurs from the late 40s to early 60s. Twice as many women than men are affected. The condition doesn’t generally run in families but there may be genetic factors that could make some people more likely to develop autoimmune conditions such as DM. There are no accurate figures on how many people are affected by DM but it is thought to be very rare with one to two people affected per 10,000.
What are the symptoms?
A red or purplish rash and other skin changes are often the predominant symptom of DM. Sometimes the rash develops before muscle problems occur.
Several types of rash may occur:
- Gottron’s sign – a scaly, patchy redness over the knuckles (and sometimes knees and elbows)
- Shawl sign – a widespread, flat, reddened area that appears on the upper back, shoulders, and back of the neck
- V sign – looks similar to the shawl sign, but appears on the front of the chest in the area of skin exposed by a V-necked t-shirt
- Heliotrope rash –blue/purple rash and swelling on the upper eyelids
- Nail abnormalities –the skin around the fingernails may become reddened
- Mechanic’s hands – a roughening and cracking of the skin of the tips and sides of the fingers
- Scalp – changes in the scalp resembling psoriasis
The rashes are made worse by exposure to ultraviolet light (sunlight) and the skin may be scaly, dry and rough.
Deposits of calcium can occur underneath the skin in hard, painful nodules – known as calcinosis. However, this is more common in juvenile DM.
In rare cases, inflammation of the fat lying just under the skin, called panniculitis, can also occur, causing tender lumps to form under the skin.
Muscle weakness starts with the muscles closest to the trunk of the body such as those in the hips, thighs, back, upper arms, neck and shoulders. The weakness usually develops over several weeks to months. This causes problems with climbing stairs, getting up out of chairs and lifting objects over the head. As the condition progresses some people may notice that muscles such as those in the forearms and ankles and wrists become weaker and there may be difficulty in holding the head up.
Muscle pain, tenderness and fatigue can be a significant problem for people with DM. In severe cases breathing problems and trouble chewing, swallowing and speaking can develop.
Other signs and complications
Rarely, DM can also affect the heart muscle, causing a condition called inflammatory cardiomyopathy. Another rare complication is inflammation of the blood vessels of the intestinal tract, eyes and kidneys, which results in damage to these organs.
People with inflammatory myopathies, especially adults with dermatomyositis have an increased risk of cancer. This risk increases with age and involves the same common cancers that affect the general population, including cancer of the lung, breast, prostate, and ovaries. As a result, people with DM may need more frequent cancer screening, especially in the first five years after diagnosis.
Often DM occurs in isolation but sometimes it is associated with “connective tissue disorders” such as rheumatoid arthritis, systemic lupus erythematosus (SLE), Raynaud’s disease, scleroderma or Sjögren’s syndrome.
What causes dermatomyositis?
The cause of DM is not well understood. It is known that it is an autoimmune condition, in which the body’s immune system mistakenly attacks small blood vessels in the muscles and under the skin. Inflammatory cells surround the blood vessels which eventually leads to degeneration of muscle fibers. What causes this autoimmune reaction is still up for debate. It is thought that in some cases viruses or certain drugs might be a trigger.
Although DM is not considered a genetic disease, there may be some genetic factors that make it more or less likely that the condition will develop.
How is dermatomyositis diagnosed?
The diagnostic process is started by a careful look at your medical history and a thorough physical exam.
Blood tests are usually the next step. Nearly all people with DM will have high levels of creatine kinase (CK) in their blood. This is a protein that normally resides in muscle but leaks out into the blood when the muscles are damaged. Blood tests may also show up antibodies that indicate an autoimmune condition. Antibodies are proteins made by the immune system. However, some people with DM will have no sign of autoimmune antibodies.
DM can easily be confused with many other muscle conditions and is difficult to diagnose, especially in the absence of antibody markers. Other tests that may be done to give extra clues and rule out other conditions include:
- magnetic resonance imaging (MRI) which can detect changes suggesting muscle inflammation
- electromyogram (EMG) which can demonstrate abnormal electrical activity in muscles and help distinguish weakness due to muscle disease from weakness due to nerve problems
- A nerve conduction velocity test measures how fast a nerve impulse travels and how strong it is
A muscle biopsy is often needed to give an accurate, definitive diagnosis. It involves removing a small piece of muscle through an incision in the skin. The specimen is examined under a microscope for evidence of blood vessels in the muscles being attacked by immune cells. Muscle cells also appear smaller than normal around the edges of bundles of muscle fibers, and capillaries are scarce in these regions.
How is it treated?
DM is a highly treatable disease with some people recovering completely, while others are able to keep the symptoms under control for long periods of time. Treatment involves drugs to control the inflammation that is causing the muscle weakness. No one treatment works for everyone and often a trial and error approach is needed to find the best combination of treatments.
Initial treatment involves high-dose corticosteroids such as prednisolone. Although this is usually effective very quickly, taking these drugs at a high dose for a long period of time carries a high risk of serious side effects. For this reason, the dosage is then tapered to reach an appropriate maintenance dose. However, corticosteroids should never be suddenly stopped or the dose reduced without checking with your doctor first.
Other drugs to suppress the immune system are often given to help reduce the dose of corticosteroid needed. These include:
- Mycophenolate mofetil
Other drugs that may help some people include cyclophosphamide and tacrolimus. Although most people tolerate these medications, some may experience side effects so it is important to be aware of the potential risks and benefits of each drug and work with your doctor to find the ideal treatment for you.
In severe cases that do not respond to other treatments, IVIg therapy is considered. This is an infusion of immunoglobulins (antibodies) which are extracted from a large pool of donated blood. It is thought that these extra antibodies confuse and interfere with the body’s immune system.
If none of the treatments mentioned above are effective, the doctor will first reconfirm the diagnosis of DM. Then drugs that have been approved to treat other autoimmune conditions may be tried such as rituximab or alemtuzumab (for more information on these types of drugs please see ‘What research is being done’ below).
Taking steroids can increase the risk of osteoporosis (brittle bones) so it is important to consider supplements of calcium and vitamin D, and hormone replacement therapy (HRT) in post-menopausal women. In some cases a group of drugs called bisphosphonates may be prescribed to help prevent steroid-induced osteoporosis.
Avoidance of sun exposure during peak hours and use of sunblock and protective clothing are recommended to avoid worsening the skin aspects of the disease.
Physiotherapy is recommended to keep the joints supple and physiotherapists can supervise an appropriate exercise program. A gentle exercise program, such as hydrotherapy in a swimming pool, can help to maintain strength and wellbeing. Some people may need a cane, walker or even a wheelchair during acute flare-ups of DM and an occupational therapist and/or physiotherapist can help with arranging these.
Careful attention to a healthy diet can help with the management of the symptoms, especially when taking corticosteroids which can lead to significant weight gain which can put extra strain on the muscles.
Regular monitoring of breathing, swallowing and heart function is recommended to allow any problems to be anticipated and treated.
What research is being done?
Much of the research into DM focuses on understanding precisely why and how the immune system attacks the blood vessels, which will lead to better treatments for the disease.
Several new drugs developed for other autoimmune diseases or for treating people who have had an organ transplant are now being tested for myositis. Some anti-cancer drugs that target cells of the immune system also show promise for inflammatory myopathies. Most of these drugs are so-called “monoclonal antibodies” and have the abbreviation “mab” at the end of their name.
Antibodies are proteins produced by the immune system that target a protein or type of cell in the body and as a result it is destroyed. An antibody preparation that is produced in the laboratory containing identical antibodies is called “monoclonal”. When used as drugs, monoclonal antibodies are designed to target a part of the body that is harmful, for example cancer cells or a component of the immune system that has become overactive in an autoimmune disease.
Tocilizumab is one example of a monoclonal antibody. This drug was developed for rheumatoid arthritis and targets a protein called “interleukin 6 receptor” which plays an important role in immune responses and inflammation. Another is rituximab which was developed to treat blood cancers such as leukemia and works by destroying one type of white blood cell (B cells). Rituximab has also been shown to be effective for a range of autoimmune disorders. The effectiveness of these and other monoclonal antibodies for inflammatory myopathies is currently being tested in clinical trials.
Another drug being tested in clinical trial for myositis is BAF312 (Siponimod). This drug, which was developed by Novartis Pharmaceuticals, acts on the cells of the immune system to inhibit their migration to the location of the inflammation. This, in turn, should lead to reduced inflammation and muscle damage. BAF312 is also clinical trial for multiple sclerosis.
A list of clinical trials for DM can be found on the clinicaltrials.gov website. Note that some of these studies are “observational” which means that no new drug or treatment is given.
For definitions of any terms that you are not familiar with please take a look at our glossary
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Revised 2 July 2018