Juvenile arthritis (JA) is a broad term for several painful conditions that affect the joints in children. Joint pain that lasts longer than six weeks in a child under age 16 may be diagnosed as some form of arthritis.

Although arthritis is frequently considered a disease of adults, children can develop some form of most kinds of arthritis. Some forms of arthritis that affect adults may even begin in childhood. Almost 300,000 American children have some form of arthritis or other rheumatic disease, according to the Centers for Disease Control and Prevention (CDC).

Most forms of arthritis are rheumatic conditions, meaning they involve some sort of inflammation, usually of the soft tissue (cartilage) or membranes (synovium) surrounding the body’s joints. Other arthritic conditions may primarily involve inflammation of supporting structures, such as muscles, ligaments or tendons. In time, the inflammation may also cause swelling, redness and difficulty moving the joints. The joint may be red, swollen and sore, although the child may not complain of pain.

For adults, the swelling and inflammation of arthritis may mean joint pain and some disability. A complication within JA is that any injury or inflammation in a joint may affect a child’s growth and development of bones, though many children eventually outgrow the symptoms of JA and are not affected by it as adults.

Arthritis develops in many ways. Most forms of JA are autoimmune disorders, in which the body attacks its own tissue in the joints. Children with JA have an abnormal immune response. Normally, the immune system protects the body from outside invaders, such as germs. Immune cells (e.g., white blood cells) attack these invaders and flush them out or make them inactive. Part of this process normally produces some inflammation in tissue.

For someone with an autoimmune response, the immune system misidentifies regular body tissue as an outside invader. It attacks the tissue and tries to destroy it. In JA, certain types of white blood cells attack parts of the synovium, causing the inflammation that characterizes arthritis. The process by which this occurs is not well understood. The synovium thickens, which causes the joint to swell.

JA usually does not develop in infancy, but can develop any other time in childhood. Certain types more commonly develop among children between the ages of 6 and 8, whereas others occur in teenagers.

JA develops in several forms, which may affect a few joints in the body or many joints. Joints commonly affected by JA include:

• Hips, knees and ankles
• Shoulders, elbows, wrists and hands
• Neck
• Lower spine
• Jaw

Many children with JA also may experience inflammations in the eye. Some of the inflammations involve the uveal tract, the middle layer of the eye that includes the iris, ciliary body and choroid. Some of these inflammations may not have symptoms but can cause vision problems if left untreated.

Other forms of JA affect the skin, causing recurrent rashes or scaly patches of skin. The most severe cases of JA affect whole body systems, including the heart, lungs, spleen, liver and lymph nodes.

The course of JA may vary. Some children may have mild joint pain for a few months or a year. For others, the symptoms are recurrent over years and may affect their activity levels and result in frequent absences from school. Children may be reluctant to exercise or participate in activities because of pain.

Researchers have found that juvenile arthritis increases the risk of fractures and possibly osteoporosis later in life. The reasons for this may include inflammation, physical inactivity, weakness, delayed puberty, inadequate nutrition and side effects of corticosteroid therapy.

In addition, even nonarthritic children who suffer athletic injuries or other trauma, such as a knee meniscus injury or a fracture, face increased risk of developing osteoarthritis in adulthood. Osteoarthritis is by far the most common form of arthritis in adults.