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Dermatomyositis (dur-muh-toe-my-uh-SY-tis) is an uncommon inflammatory disease marked by muscle weakness and a distinctive skin rash.

The condition can affect adults and children. In adults, dermatomyositis usually occurs in the late 40s to early 60s. In children, it most often appears between 5 and 15 years of age. Dermatomyositis affects more females than males.

There's no cure for dermatomyositis, but periods of symptom improvement can occur. Treatment can help clear the skin rash and help you regain muscle strength and function.

The signs and symptoms of dermatomyositis can appear suddenly or develop gradually over time. The most common signs and symptoms include:

• Skin changes. A violet-colored or dusky red rash develops, most commonly on your face and eyelids and on your knuckles, elbows, knees, chest and back. The rash, which can be itchy and painful, is often the first sign of dermatomyositis.
• Muscle weakness. Progressive muscle weakness involves the muscles closest to the trunk, such as those in your hips, thighs, shoulders, upper arms and neck. The weakness affects both the left and right sides of your body, and tends to gradually worsen.

Seek medical attention if you develop muscle weakness or an unexplained rash.

The cause of dermatomyositis is unknown, but the disease has much in common with autoimmune disorders, in which your immune system mistakenly attacks your body tissues.

Genetic and environmental factors also might play a role. Environmental factors could include viral infections, sun exposure, certain medications and smoking.

While anyone can develop dermatomyositis, it is more common in people assigned female at birth. Genetics and environmental factors including viral infections and sun exposure also may increase the risk of developing dermatomyositis.

Possible complications of dermatomyositis include:

• Difficulty swallowing. If the muscles in your esophagus are affected, you can have problems swallowing, which can cause weight loss and malnutrition.
• Aspiration pneumonia. Difficulty swallowing can also cause you to breathe food or liquids, including saliva, into your lungs.
• Breathing problems. If the condition affects your chest muscles, you might have breathing problems, such as shortness of breath.
• Calcium deposits. These can occur in your muscles, skin and connective tissues as the disease progresses. These deposits are more common in children with dermatomyositis and develop earlier in the course of the disease.

Associated conditions

Dermatomyositis might cause other conditions or put you at higher risk of developing them, including:

• Raynaud's phenomenon. This condition causes your fingers, toes, cheeks, nose and ears to turn pale when exposed to cold temperatures.
• Other connective tissue diseases. Other conditions — such as lupus, rheumatoid arthritis, scleroderma and Sjogren's syndrome — can occur with dermatomyositis.
• Cardiovascular disease. Dermatomyositis can cause heart muscle inflammation. In a small number of people who have dermatomyositis, congestive heart failure and heart rhythm problems develop.
• Lung disease. Interstitial lung disease can occur with dermatomyositis. Interstitial lung disease refers to a group of disorders that cause scarring of lung tissue, making the lungs stiff and inelastic. Signs include a dry cough and shortness of breath.
• Cancer. Dermatomyositis in adults has been linked to an increased likelihood of developing cancer, particularly ovarian cancer in women. Risk of cancer appears to level off three years or so after a diagnosis of dermatomyositis.

If your doctor suspects that you have dermatomyositis, he or she might suggest some of the following tests:

• Blood analysis. A blood test will let your doctor know if you have elevated levels of muscle enzymes that can indicate muscle damage. A blood test can also detect autoantibodies associated with different symptoms of dermatomyositis, which can help in determining the best medication and treatment.
• Chest X-ray. This simple test can check for signs of the type of lung damage that sometimes occurs with dermatomyositis.
• Electromyography. A doctor with specialized training inserts a thin needle electrode through the skin into the muscle to be tested. Electrical activity is measured as you relax or tighten the muscle, and changes in the pattern of electrical activity can confirm a muscle disease. The doctor can determine which muscles are affected.
• MRI. A scanner creates cross-sectional images of your muscles from data generated by a powerful magnetic field and radio waves. Unlike a muscle biopsy, an MRI can assess inflammation over a large area of muscle.
• Skin or muscle biopsy. A small piece of skin or muscle is removed for laboratory analysis. A skin sample can help confirm the diagnosis of dermatomyositis. A muscle biopsy might reveal inflammation in your muscles or other problems, such as damage or infection. If the skin biopsy confirms the diagnosis, a muscle biopsy might not be necessary.

There's no cure for dermatomyositis, but treatment can improve your skin and your muscle strength and function.

Medications

Medications used to treat dermatomyositis include:

• Corticosteroids. Drugs such as prednisone (Rayos) can control dermatomyositis symptoms quickly. But prolonged use can have serious side effects. So your doctor, after prescribing a relatively high dose to control your symptoms, might gradually reduce the dose as your symptoms improve.
• Corticosteroid-sparing agents. When used with a corticosteroid, these drugs can decrease the dose and side effects of the corticosteroid. The two most common medications for dermatomyositis are azathioprine (Azasan, Imuran) and methotrexate (Trexall). Mycophenolate mofetil (Cellcept) is another medication used to treat dermatomyositis, particularly if the lungs are involved.
• Rituximab (Rituxan). More commonly used to treat rheumatoid arthritis, rituximab is an option if initial therapies don't control your symptoms.
• Antimalarial medications. For a persistent rash, your doctor might prescribe an antimalarial medication, such as hydroxychloroquine (Plaquenil).
• Sunscreens. Protecting your skin from sun exposure by applying sunscreen and wearing protective clothing and hats is important for managing the rash of dermatomyositis.

Therapy

Depending on the severity of your symptoms, your doctor might suggest:

• Physical therapy. A physical therapist can show you exercises to help maintain and improve your strength and flexibility and advise you about an appropriate level of activity.
• Speech therapy. If your swallowing muscles are affected, speech therapy can help you learn how to compensate for those changes.
• Dietetic assessment. Later in the course of dermatomyositis, chewing and swallowing can become more difficult. A registered dietitian can teach you how to prepare easy-to-eat foods.

Surgical and other procedures

• Intravenous immunoglobulin (IVIg).  IVIg is a purified blood product that contains healthy antibodies from thousands of blood donors. These antibodies can block the damaging antibodies that attack muscle and skin in dermatomyositis. Given as an infusion through a vein, IVIg treatments are expensive and might need to be repeated regularly for the effects to continue.
• Surgery. Surgery might be an option to remove painful calcium deposits and prevent recurrent skin infections.

With dermatomyositis, areas affected by your rash are more sensitive to the sun. Wear protective clothing or high-protection sunscreen when you go outside.

Living with a chronic autoimmune disease can make you wonder whether you're up to the challenge. To help you cope, try the following:

• Know your illness. Read all you can about dermatomyositis and other muscle and autoimmune disorders. Talk to people who have a similar condition. Don't be afraid to ask your doctor questions concerning your illness, diagnosis or treatment plan.
• Be a part of your medical team. Consider yourself, your doctor and other medical experts involved in your care as a united front in the management of your disease. Following the treatment plan you agreed to is vital. Keep your doctor updated on any new signs or symptoms you develop.
• Get active. A regular exercise routine can help you maintain and build your muscle strength. Be sure to get a detailed plan and recommendations from your doctor or physical therapist before starting an exercise program.
• Rest when you're tired. Don't wait until you're exhausted. This will only set you back further as your body tries to recuperate. Learning to pace yourself can help you maintain a consistent level of energy, accomplish just as much and feel better emotionally.
• Acknowledge your emotions. Denial, anger and frustration are normal when dealing with dermatomyositis. Feelings of fear and isolation are common, so stay close to your family and friends. Try to maintain your daily routine as best you can and don't neglect doing things you enjoy. Many people find support groups helpful.

You're likely to first see your family doctor, who might refer you to a doctor who specializes in the treatment of arthritis and other diseases of the joints, muscles and bones (rheumatologist) and to a doctor who specializes skin diseases (dermatologist).

What you can do

Make a list that includes:

• Detailed descriptions of your symptoms and when they began
• Information about medical problems you've had, and those of your parents or siblings
• All the medications and dietary supplements you take and their doses
• Questions to ask the doctor

Take a family member or friend along, if possible, to help you remember the information you're given.

For dermatomyositis, questions to ask your doctor include:

• What is likely causing my symptoms?
• What are other possible causes?
• Are my symptoms likely to change over time?
• What tests might I need? Are special preparations required?
• Are treatments available for my condition? What treatments do you recommend?
• I have other medical conditions. How can I best manage them together?
• Do you have brochures or other printed material I can have? What websites do you recommend?

Don't hesitate to ask other questions.

What to expect from your doctor

Your doctor will likely ask you questions, such as:

• Did your condition develop gradually or come on suddenly?
• Are you easily fatigued during waking hours?
• Does your condition limit your activities?
• Has anyone in your family been diagnosed with a condition that affects the muscles?
• What, if anything, seems to improve your symptoms?
• What, if anything, appears to worsen your symptoms?