The term Juvenile Myositis (JM) refers to a group of rare conditions belonging to the group Idiopathic Inflammatory Myositis (IMM). The common feature of all IMM is the presence of myositis, which means inflammation in the muscles. "Idiopathic" means that we do not know exactly the causes of these diseases. “Juvenile” refers to the symptoms of disease appearing before the age of 16 years.
Among JM we mainly recognize two different conditions, named Juvenile Dermatomyositis (JDM) and Juvenile Polymyositis (JPM). Because of the fact that JDM is the most common type of IIM in children, most research has been done on this disease and the information you will find in the following paragraphs refer specifically to JDM. Therefore, not all the information you will find below will apply to your child if their diagnosis is different from JDM. Because of the rarity of the other conditions belonging to the group named JM, we don’t have so much evidence, and details; these kinds of JM are still the subject of extensive research.
Dermatomyositis is a disease which mainly affects the skin (dermato) and the muscles (myositis). Some children/young people may have muscle inflammation without a rash or skin problems. In some cases, a rash can occur later but a small number of children/young people never have skin problems and their disease is called Polymyositis. Not having a skin rash can make it hard to know if your child has the illness. Your child’s hospital doctor will carry out tests to make sure that there are no other reasons for the muscle weakness and that your child does have JDM or JPM.