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Information // Guide to Juvenile Dermatomyositis

What is JDM?
Juvenile Dermatomyositis (JDM) is an autoimmune disease affecting approximately 3 children in every million per year. Muscles weakness and skin rash are the main symptoms of JDM and it affects every child differently with some children experiencing a mild form of the disease while others display a more severe disease progression.

What is the origin of the disease?
The immune system is a group of cells that normally protects the body from infection. In autoimmune diseases like JDM, these cells appear to react against the body itself. This process damages the body instead of protecting it. In JDM sufferers, the skin rash and weak muscles are caused by inflammation in the skin and in the muscles, and may affect blood vessels and other systems such as the lungs and gut.

What causes JDM?
Many researchers worldwide are looking into the cause of JDM and some believe that there is a genetic predisposition to autoimmune diseases. Children afflicted with JDM may have a relative who suffers from another autoimmune disease such as diabetes or arthritis. The autoimmune disease usually presents itself when a "trigger" causes the body's immune system to overreact. Although research has not identified any one specific trigger it is believed triggers could include viruses, or an environmental hazard.

What are the symptoms of JDM?
The main symptoms of JDM are weak painful muscles, rashes, tiredness, irritability and fever. Some children can also have joint pains.

Weak muscles
The muscles that are affected the most are those near the trunk of the body: the upper arms, the thighs, the neck and the trunk itself. Other muscles can become weak and children can have difficulty swallowing, or develop changes in their voice. Occasionally there is inflammation in the gut, which can cause bowel problems. Children with JDM can have difficulty getting up from bed, climbing stairs and getting up from the floor or from a chair. Walking and running can become challenging and exhausting. Musscle weakness can be assessed by doctors using specific outcome measures such as the Childhood Muscle Assessment Score (CMAS.pdf) and the MMT8 (MMT8.pdf)

Skin rash
The skin rash in JDM usually occurs on the face, knuckles, elbows, knees and ankles. The rash may appear before, after or at the same time as the muscle weakness. Sometimes the rash is so faint that it is not noticeable. The rash appears as a red purplish colour on the eyelids and cheeks; whereas the rash looks like red dry skin patches over the knuckles, elbows and knees. The fingernails and the nailbeds may take on a pinkish colour as well. Sometimes, the children develop Gottron's Papules, which are small bumps that appear over the finger joints. They can look like small blisters. 

With JDM, children can tire easily and sometimes can only walk short distances. Children may need to rest often and lack the energy for normal activities. It can become difficult for children to keep up with friends.
You may notice your child seems quite irritable and their behaviour may become more difficult than normal.

Sometimes, children with JDM run low-grade fevers, which can be at night.

What are other possible symptoms?
The following symptoms of JDM are less common, but important to understand:

Ulcers can occur in the skin, and can look like sores within the skin rash. They can be deep or on top of the skin and they also range in size. The ulcers can be painful, but will usually go away with treatment.

Contractures are shortened muscles that cause a joint to stay in a bent position. These can occur due to lack of movement or due to muscle inflammation.

Some children with JDM can develop calcinosis, which are small lumps of calcium that form under the skin or in the muscle. They may feel like little rocks under the skin and can range in size from a dot to a large pebble.
Other symptoms
Some children with JDM have problems with joints, tightness of the skin, and painful fingers in the cold ; some of theseproblems can happen in other diseases as well like a condition called lupus.

What tests are used to diagnose JDM?
If JDM is suspected, blood tests are the first step to confirm there is a problem. Muscle enzymes are measured, including CK – creatine kinase and LDH – lactate dehydrogenase, which are enzymes that leak from inflamed or damaged muscles into the bloodstream. Blood tests also show if the child's body is producing antibodies (like Antinuclear antibodies, or ANA) against its own cells.

The next step is generally an MRI (Magnetic Resonance Imaging), which can also detect muscle inflammation, and sometimes other types of  xray.

A muscle biopsy may be performed (usually under general anaesthetic) to confirm the diagnosis. A small amount of muscle (from the thigh) may be removed for examination to determine if and how much the muscles and blood vessels have been affected by the disease.

What is the treatment for JDM?
There is no cure for JDM yet, but there are treatment options to help manage the symptoms. Early treatment is usually the best predictor of a better outcome of this disease. See the Treatment page that gives more information on the different types of treatment available.

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