Juvenile inflammatory myopathy is a group of diseases causing inflammation of the muscles and other symptoms. There are three major types: polymyositis, sporadic inclusion body myositis and dermatomyositis (with dermatomyositis being clearly the most common).

The disease typically causes muscle weakness — especially in the muscles nearest to the center of the body, joint pain, fatigue and clumsiness. It can cause a pinkish-purple rash in a mask-like pattern on the face and around the joints. It may also result in irritability, weight loss and ulcers in the mouth. Not all symptoms develop simultaneously, which sometimes making diagnosis difficult.

It is commonly treated with a combination of prednisone and methotrexate, along with topical medications as needed.