Juvenile dermatomyositis

Muscle is a tissue made up of fibers that join together to form bundles. There are 3 types of muscle: striated, smooth and cardiac.

• Striated muscle: it is attached to the bone through tendons. Its contraction is necessary for the movement of the locomotor apparatus. They are covered by a membrane called fascia. Their contraction is voluntary (they receive an order from our central nervous system to contract).
• Smooth muscle: forms part of some internal organs such as the gastrointestinal tract and blood vessels. Its contraction is not voluntary (it depends on the autonomic nervous system).   
• Cardiac muscle: also called myocardium. It is responsible for pumping blood to reach our organs through the circulatory system.

In JDM the most frequently affected muscle is the striated muscle. Sometimes there is inflammation of the fascia (fasciitis) or of the myocardium (myocarditis).