Dermatomyositis: What to Know About This Autoimmune Condition

Dermatomyositis — what a mouthful! But the name tells us exactly what it is. “Dermato” means skin. “Myo” means muscle. “Itis” means inflammation. So, dermatomyositis is a condition that causes inflammation in the skin and muscles. This inflammation leads to rashes, muscle weakness, and other symptoms.

Dermatomyositis is part of a family of autoimmune diseases called the “inflammatory myopathies.” Polymyositis — a similar condition that causes muscle weakness without the rashes — is in this family too.

Dermatomyositis is rare; it affects only 1 in 100,000 people per year. It occurs in both children and adults, and it’s more common in women than men. It’s a lifelong condition that can have severe complications. But treatments like immunosuppressants, steroids, and exercise can help you manage this condition.

What causes dermatomyositis?

The immune system is the body’s army. It helps protect you against things that don’t belong, like bacteria. But sometimes the immune system gets confused and attacks your own body instead. This is an autoimmune disease (“auto” means self).

Experts aren’t exactly sure what causes autoimmune diseases like dermatomyositis. Certain genes can make a person more likely to develop dermatomyositis one day. Then, a trigger from the environment gets the immune system’s attention, but it goes a bit too far. And the end result is dermatomyositis.

Let’s say you get the flu. The immune system wakes up to fight the virus, but it doesn’t stop there. It accidentally attacks the skin and muscles, too. Cancer can also trigger the immune system. That’s why healthcare providers screen for cancer after diagnosing dermatomyositis.

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What are the symptoms of dermatomyositis?

Dermatomyositis is more than just a skin and muscle disease. It can affect many different parts of the body, and the symptoms depend on the organs it affects. 

Every person has their own version of dermatomyositis with their own unique mix of symptoms. Some symptoms are present at diagnosis, but others may appear later. Some symptoms may never occur at all. And symptoms can wax and wane.

Skin

Dermatomyositis rashes are reddish-purple, flaky, and itchy. They may discolor the skin after they heal (like a scar). The rashes can affect any part of the skin, but they particularly like these areas:

• Scalp

• Chest

• Upper back and shoulders

• Sides of thighs

• Knuckles

• Knees and elbows

• Eyelids (purple discoloration and swelling)

Dermatomyositis can also cause skin ulcers and calcinosis (hard, white lesions underneath the skin due to calcium buildup).

Muscles

Dermatomyositis affects the muscles closest to the trunk of the body, like the neck, shoulder, and thigh muscles. Inflammation in these muscles causes weakness, but it usually isn’t painful. 

For example, it may be difficult to stand up from a chair without help from your arms to push you up. It might be difficult to hold your arms overhead while blow-drying your hair or talking on the phone. Or it might be hard to hold your head upright.

Sometimes dermatomyositis affects the muscles of the throat. This can cause difficulty swallowing and/or choking on food and liquids. This is an emergency that requires care in a hospital.

Here’s the good news: With treatment, muscle strength returns to normal for most people.

Heart and lungs

Dermatomyositis can cause inflammation in the heart and lungs. When this occurs, symptoms include shortness of breath, cough, and/or swelling of the legs. 

Other

Dermatomyositis can also cause these symptoms:

• Joint pain and swelling

• Color changes of the fingers and toes when exposed to cold temperatures (Raynaud’s phenomenon)

• Fever

• Weight loss and lack of appetite

• Fatigue

How do you diagnose dermatomyositis?

Dermatomyositis is a clinical diagnosis. That means there’s no single test to diagnose it. Healthcare providers use clues from your symptoms and physical exam to arrive at the diagnosis. 

Sometimes they can make the diagnosis based on the rash and muscle weakness alone. But if the diagnosis isn’t clear, they may order additional tests to help diagnose dermatomyositis. These tests may include: 

• Blood tests: These may include creatine kinase (a muscle test) and autoantibodies (autoimmune tests).

• Biopsies of skin or muscle: These are minor procedures where your provider takes a small piece of tissue and studies it under a microscope.

• Electromyography (EMG): This tests how nerves communicate with muscles.

• MRI (magnetic resonance imaging): An MRI of the shoulder or thigh muscles can look for inflammation.

• CT (computed tomography) scan: A CT scan of the chest looks for inflammation in lungs.

Dermatomyositis is typically diagnosed by a dermatologist (skin specialist), rheumatologist (autoimmune disease specialist), or neurologist (brain and spinal cord specialist).

How do you treat dermatomyositis?

Since dermatomyositis is different for every person who has it, there’s no one-size-fits-all approach to treatment. But treatment often follows these general steps:

• Stop inflammation quickly with steroids (prednisone). 

• Use immunosuppressants (like mycophenolate mofetil) to turn off the immune system’s attack on the body, so steroids are no longer necessary. This is important because steroids have many long-term side effects, like high blood sugar, bone loss, and high blood pressure. Of note, most immunosuppressants for dermatomyositis are used “off-label.” This means that they aren’t FDA approved, but scientific studies show they’re safe and effective. 

• Get exercise and physical therapy. Exercise is great for muscles affected by dermatomyositis. It’s natural to worry that working your muscles when they’re weak could make them worse. But the opposite is true. Exercise reduces inflammation, improves fatigue, and helps regain normal muscle strength sooner.

Is there a cure for dermatomyositis?

No. Dermatomyositis is a chronic condition, but that doesn’t mean there isn’t hope. There are many treatments that control symptoms. It may take a bit of trial and error to find the medication or combination of medications that work for you. But there’s a regimen out there that can get you feeling better soon.

What happens if you don’t treat dermatomyositis?

Left untreated, dermatomyositis is progressive and can be life-threatening. Complications depend on which organs are involved. For example, severe lung inflammation requires treatment with strong immunosuppressants (like cyclophosphamide, a chemotherapy). If inflammation doesn’t respond to these medications, lung transplant may be necessary.

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Written by:

Samantha C. Shapiro, MD

Samantha Shapiro, MD, is a board-certified rheumatologist and internist with expertise in autoimmune and inflammatory conditions. She founded the division of rheumatology at Dell Medical School at The University of Texas at Austin.

Edited by:

Mandy Armitage, MD

Mandy Armitage, MD, has combined her interests in clinical medicine with her passion for education and content development for many years. She served as medical director for the health technology companies HealthLoop (now Get Well) and Doximity.

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