Juvenile dermatomyositis (JDM) is a disease in children that causes skin rash (dermato) and muscle inflammation (myositis) resulting in weak muscles. JDM is a type of autoimmune disease, where cells fight the body's own tissues and cells, resulting in inflammation and tissue damage.
JDM occurs in children under the age of 16 and affects 3,000-5,000 children in North America. JDM occurs twice as often in girls as in boys. The average age of onset is 7 years and rarely occurs under the age of 2. JDM is found worldwide, but it is more frequently seen in North America and it may be more common in the African-American population. There seems to be a clustering of new cases in the spring and summer.
The cause of JDM is unknown. One view commonly held by researchers in this area (but not scientifically proven) is that myositis requires the combination of two factors - infection and genetics. In this theory, the body has an abnormal response to a virus infection. The immune system attacks and clears the virus, but does not stop this process and begins attacking the body's own tissue(s). There is some evidence to show that some people are more likely to have this type of abnormal immune response and that this tendency for the immune system to act this way is at least partially inherited. This is not a simple genetic inheritance we see in other types of muscle disease like muscular dystrophy. It is very, very rare for other family members to develop JDM. In some people there appear to be genes, or groups of genes, which either allow the immune system to cause the illness to occur or fail to protect the person from developing it.
JDM is not contagious.
JDM is different from adult dermatomyositis. In JDM, there is no increased risk of cancer. However, blood vessel involvement is frequent and often severe. Also, calcium deposits (calcinosis) are common, especially in the recovery phase.
In most children, the onset of JDM is characterized by fever in the range of 101-104º and easy fatigue. Almost all children with JDM have less energy and do fewer activities or just refuse to do certain tasks because they know they cannot do them successfully. Weight loss and poor appetite may occur.
The following is a list of the most common symptoms seen in JDM patients. If any of these occur in your child you need to contact your doctor immediately.
Skin Rash - the first sign of JDM is often slow development of a skin rash. You may notice your child's eyelids and cheeks become red or purplish, and the eyelids may become puffy. Red patches that look like dry skin appear over the knuckles, elbows, and knees. The rash gets worse in sunlight.
Muscle Weakness - the muscles closer to the trunk (neck, shoulders, hips) will slowly become very weak. Common movements like climbing stairs and getting up from the floor or chair may become difficult. Your child may complain that their muscles are sore and that they have less energy. In very severe cases of JDM, the muscles used for swallowing can be affected. This can result in choking on food. Your child's voice may also sound faint.
Stiff and swollen joints - the joints, or the muscles around them, may become inflamed. The inflammation doesn't usually last long or cause joint damage.
Contractures - a contracture is a shortened muscle that causes a joint to remain in a bent position. This can happen during the healing process (as the muscle heals, it may scar) or through lack of exercise. Contractures can be avoided by daily exercises and physical therapy.
Ulcers - ulcers are caused by breakdown of the tissue surrounding an involved blood vessel that is not providing enough circulation to the tissue. These ulcers most commonly occur in the skin and gastrointestinal tract. When they occur in the skin, they are sores that have a crater like appearance with an obvious border to the ulcer. These ulcers are very slow to heal and do not scab easily. They vary in severity of pain from painless to very painful. JDM related ulcers can occur in any part of the gastrointestinal tract (from the esophagus to the rectum). Your child may complain of pain with swallowing, severe abdominal pain, or bloody stools. In some cases there is very little pain but just dark or bloody stools.
Calcium deposits - Some children with JDM develop calcium deposits under the skin or in the muscle. The calcium deposits vary in size but are always firm feeling - like little rocks under the skin. Deposits in the muscle can impair muscle movement. In some cases these calcium deposits will break through the skin and drain. These draining areas may become infected.
JDM is a treatable disease. Most children go into remission within two years and may have their medications eliminated. However, some children may have active disease longer than two years, and some may have more severe symptoms than others. Some children with JDM can have repeat episodes of the disease or may have the type of disease that does not easily respond to medications. Despite the challenges children with JDM and their families face, the majority of children grow up to lead an active, productive life.
There is no cure for JDM. However, there are effective treatments that can reduce or eliminate the symptoms and allow people with JDM to lead active, healthy lives. The goals of any treatment program for JDM are to:
To reach these goals, doctors work with families to find a treatment plan that works best for them. Treatment usually includes medication, physical therapy, and education. As your child's symptoms change, the treatment plan may also be changed.