Juvenile dermatomyositis (JDM) is a kind of arthritis that happens in kids. It's a rare disease that causes inflammation and swelling of the muscles and blood vessels under the skin. It may also be called inflammatory myopathy.
About 3,000 to 5,000 children in the United States have JDM. It most often affects kids ages 5 to 10. (In adults, it's called dermatomyositis.)
Scientists aren't sure what causes this type of arthritis. It's thought of as an autoimmune disorder -- that means the immune system mistakenly attacks muscle cells and blood vessels in the skin.
Symptoms
The most common signs of JDM are muscle pain, weakness, and a rash. About half the kids with the condition have weak muscles, especially in the muscles closer to the torso, hips, thighs, shoulder, and neck. This affects both sides of the body and tends to get worse over time
Your child may not tell you their muscles feel weak. Here are some signs to watch for:
- They have a hard time getting out of a chair.
- They can't lift their arms above their head (if they're brushing their hair, for example).
- They turn over in bed slowly.
- They have trouble climbing stairs.
- They fall sometimes for no reason.
A skin rash may show up with the muscle weakness, or it may appear months later. The symptoms may be mild to severe. The rash may look like:
- A red, purple rash on their cheeks and eyelids
- A patchy rash on the skin around the nails, elbows, chest, back, and knees
- Redness or swelling near their fingernails
- Skin ulcers (open wounds on their skin)
Sometimes, the rash may look like eczema.
Other symptoms of JDM depend on the area of your child's body that's affected. They may include:
- Hard lumps of calcium under their skin (calcinosis)
- Joints that are strangely bent (contractures)
- Weak voice
- Hard time swallowing
- Fatigue, fever, and weight loss
- Problems breathing (which can be life threatening)
- Stomach aches
Diagnosis
If your child has a skin rash or muscle weakness, make an appointment with their pediatrician. Early diagnosis of JDM is important to prevent permanent muscle damage.
Your child's doctor will ask questions about their symptoms and medical history. Certain tests can help diagnose JDM or rule out other conditions. They include:
- Blood tests to check for proteins linked to inflammation or things called autoantibodies that are related to JDM.
- Electromyography, or EMG, to measure the electric activity of your child's muscles and find the location of the disease. Small patches are put on your child's skin, and wires connect them to the machine that records the activity.
- Magnetic resonance imaging (MRI) to spot early signs of muscle inflammation and swelling. This uses powerful magnets and radio waves to make a detailed image of the affected areas of your child's body.
- Muscle biopsy to check for signs of inflammation or infection. A small piece of muscle tissue is taken to be looked at under a microscope.
- A close look at nails and cuticles with a lighted magnifying glass (nailfold capillaroscopy) to spot active signs of the disease.
Treatment
There's no known cure for JDM. But early treatment can help prevent permanent health issues. Treatment involves medication, physical therapy, and speech therapy, depending on your child's symptoms.
- Medications: Powerful anti-inflammatory drugs called corticosteroids, usually prednisone, are tried first to help with symptoms. Your child will take these for a long time (sometimes for years). They can work quickly but often have side effects, some serious. Long-term use of corticosteroids may affect your child's bone growth and eyesight. Another drug, called methotrexate, is often given along with prednisone. Sometimes, non-steroid medications may be prescribed. They include IV immunoglobulin, cyclosporine, azathioprine, tacrolimus, hydroxychloroquine, and mycophenolate mofetil. For very severe symptoms, anti-tumor necrosis factor (anti-TNF) drugs or rituximab may be used. Always ask your child's doctor about the expected side effects.
- Physical therapy (PT): Your child's therapist will teach them stretches and exercises to strengthen muscles and prevent weakness.
- Speech therapy: JDM can damage the muscles your child uses to talk. Speech therapy can help.
- Dietary help: Muscle weakness in your child's tongue, throat, and neck can make it difficult for them to chew and swallow food. Soft foods can be easier to eat. A registered dietician can show you how to make a proper, balanced food plan. More protein may be recommended to make up for muscle damage. If eating is especially difficult, your child may need a feeding tube.
With proper treatment, signs of the disease can go away (go into remission). But some children have long-lasting symptoms that don't get better with treatment.
How Else Can I Help My Child?
Juvenile dermatomyositis is a lifelong disease. It's important to make sure your child sticks to their treatment plan and remains in the best possible health. Here are some ways you can help them do that:
- Make sure your child gets plenty of exercise. Physical activity keeps muscles strong and joints healthy. Exercise also helps keep a healthy body weight.
- Use sunscreen. Ultraviolet rays from the sun can make your child's skin rash worse. Choose one that protects against UVA and UVB light. Wide-brimmed hats and photo-protective clothing are also helpful.
- Tell your child's teachers and school leaders about their disease. This is especially important because they may not appear sick.
