Juvenile dermatomyositis (JDM) is a rare autoimmune condition, meaning that the immune system malfunctions and attacks the body's organs and tissues, which in JDM, includes the muscles and skin. Dermatomyositis is defined as "juvenile" when it starts before the age of 16.
In JDM, the small blood vessels in the skin (dermato-) and the muscles (myositis) are affected. This leads to problems such as muscle weakness and/or pain, especially in the muscles of the trunk and those around the hips, shoulders and neck. Most young people have typical skin rashes as well. These rashes can affect several areas of the body, including the face, eyelids, knuckles, knees and elbows. The skin rash does not always occur at the same time as the muscle weakness - it can develop before or after it. In rare cases, small blood vessels in other organs can also be involved.
JDM is a rare disease in children and young people. Approximately 4 in 1 million children will develop JDM each year. It is more common in girls than in boys. It most often starts between the ages of 4 and 10 years, but children of any age can develop JDM.