The underlying process is an inflammation of small blood vessels (vasculitis) which is thought to result from the presence in the blood of circulating immune complexes – combinations of antigen and antibody which are potent stimulators of inflammation.
Juvenile dermatomyositis is very rare. We think that it may arise in children who have a particular genetic predisposition, which may cause problems in clearing certain viruses from the system. However, it is not contagious or catching, and it does not affect other family members.