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Dermatomyositis is a rare disease marked by increasing muscle weakness, skin rash and inflammation, and swelling of the eyelids.  

Dermatomyositis is one of a group of muscle diseases that cause muscle swelling, or inflammatory myopathies (myos comes from the Greek word for muscle). It's different from other muscle diseases because it also causes skin changes. Some people with the disease also have a connective tissue disorder such as rheumatoid arthritis.

Dermatomyositis can occur at any age, but the average age at the time of diagnosis is 40. Women are twice as likely as men to be diagnosed with this disease.

Causes of dermatomyositis

The exact cause is not known, but possible causes include:

  • Abnormal genes you are born with

  • Cancer, especially in older people

  • Autoimmune disease; this is a disease that causes your body's immune system, or natural defense system, to turn against you

  • An infection, medication, or another exposure in your environment that triggers the disease

Signs and symptoms of dermatomyositis

The signs and symptoms of dermatomyositis are caused by swelling and inflammation in the blood vessels that supply your skin and muscles.

Anatomy of the skin

Inflammation of blood vessels is called vasculitis. Some people have muscle symptoms without skin symptoms, and this is called polymyositis. Others have skin symptoms without muscle symptoms, a condition called amyopathic dermatomyositis.

You could have any of these signs and symptoms if you have dermatomyositis:

  • Red to purple rash on sun-exposed areas that may be painful or itchy

  • Red to purple swelling of the upper eyelids

  • Red to purple spots on the knuckles, elbows, or knees

  • Scaly, rough, dry skin

  • Swollen, red areas around the fingernails

  • Hard lumps under the skin caused by calcium deposits

  • Muscle weakness in the neck, hip, back, and shoulders

  • Difficulty swallowing and voice changes

  • Tiredness, fever, and weight loss

  • Muscle aches

  • Trouble rising from a chair or getting out of bed because of muscle weakness

Seventy percent of people with dermatomyositis have spots on the knuckles, elbows, or knees. Thirty to 60 percent have discoloration and swelling of the eyelids. Sometimes the muscle weakness also spreads to the heart, GI tract, and lungs and can cause breathing difficulties and coughing. Adults may develop a low-grade fever, along with lung inflammation and sensitivity to light.

Diagnosis and treatment of dermatomyositis

Here are some common diagnostic tests for dermatomyositis:

  • Blood tests may be done to look for signs of muscle inflammation and abnormal proteins, called antibodies, which form in autoimmune disease.

  • Electromyelogram, or EMG, may be done to detect abnormal electrical activity in affected muscles.

  • MRI scan may be done to look for inflammation.

  • Skin or muscle biopsy may be done to look for tissue changes caused by dermatomyositis.

Dermatomyositis can't be cured, but treatment helps control the signs and symptoms of the disease for most people. There is no single best treatment for dermatomyositis—you may need more than one kind of treatment, and your treatment may need to be changed over time.

Common treatments include:

  • Physical therapy. You may need special exercises to stretch and strengthen your muscles.

  • Skin treatment. You may need to avoid sun exposure and wear sunscreen to help prevent skin rashes. Your doctor can treat itchy skin rashes with antihistamine drugs or with anti-inflammatory steroid creams that are applied to the skin.

  • Anti-inflammatory medications. Steroid drugs, or corticosteroids, that block inflammation may be given by mouth or directly into the bloodstream.

  • Immunosuppressive drugs. If steroid drugs are not working for you, other options include drugs that block or slow down, or suppress, your body's immune system. These include the drugs azathioprine, methotrexate, cyclosporine, cyclophosphamide, and tacrolimus.

  • Immunoglobulin. If you have not responded to other treatments, these drugs may be given directly into your bloodstream. Immunoglobulins are donated blood products that may boost your body's immune system.

If you have dermatomyositis, you may need to be treated for the rest of your life. It's important to learn as much as you can about your disease and work closely with your doctor. Researchers are actively studying causes and treatments for dermatomyositis. It is likely that early diagnosis and treatment for this disease will continue to improve over time.