Though often associated with aging, certain types of arthritis can actually occur as early as infancy. In children, the most common form is called juvenile rheumatoid arthritis (JRA), which, in some cases, is quite different from adult RA.

Although the term JRA brings to mind a single disease similar to "adult" rheumatoid arthritis, it is actually an umbrella term for three forms of childhood arthritis (two of which have further subtypes), each with a different pattern and prognosis.

Systemic Onset JRA (also called Still's disease)

As the name suggests, systemic onset JRA affects many bodily systems. It often begins with a fever and chills that appear off and on for weeks and may be accompanied by a rash on the thighs and chest. In addition to inflamed joints, a child may experience enlargement of the spleen and lymph nodes; inflammation of the liver, heart and surrounding tissues; and anemia.

Polyarticular JRA

Meaning many joints, this type of JRA affects more than four joints. Joints most commonly affected are the small joints of the hands as well as the knees, ankles, hips and feet. Joint involvement is usually symmetrical, meaning if a joint on the left side is affected, its counterpart on the right side is affected as well.

Polyarticular JRA has two subtypes. The first is characterized by the presence of rheumatoid factor, a type of autoantibody found in the blood of adults with RA, and the DR4 genetic type, also common in adults with RA. The pattern of this subtype resembles adult RA and has the potential to severely damage joints.The second subtype is characterized only by joint involvement. Children with this subtype do not have a positive rheumatoid factor and the arthritis is potentially less severe.

Pauciarticular JRA

Meaning few joints, pauciarticular JRA generally affects four or fewer joints in an asymmetrical fashion. (That is, if one elbow or knee is affected, the opposite elbow or knee isn't.) The joints most likely to be affected are the knees, elbows, wrist and ankles. Pauciarticular JRA has three subtypes.

In the first subtype of pauciarticular JRA, children test positive for antinuclear antibodies and have a high risk of iridocyclitis, a potentially dangerous inflammation of the eye.

In the second subtype, arthritis affects the spine as well as other joints, although spinal involvement may not occur until the child reaches his late teens. Children with this subtype may test positive for the HLA-B27 gene, which is common in adults with ankylosing spondylitis. In fact, some doctors refer to this subtype of JRA as juvenile ankylosing spondylitis.

In the third subtype, joint involvement is the extent of the disease.

What Causes JRA?

The cause is not known; it's likely there are probably many causes, including genetics and environmental factors such as a virus or bacterium, that trigger the disease in children with a genetic predisposition.

Who Gets It?

JRA can occur in boys or girls of any age, but it most commonly begins during the toddler or early teenage years. Certain types and subtypes are more prevalent in boys than girls and vice versa. In general, it affects more girls than boys. Certain subtypes are more likely to occur in children of a particular age.

How Is It Diagnosed?

Diagnosing JRA involves a medical history, physical exam and possibly laboratory tests, including blood tests to measure inflammation and to detect antinuclear antibodies, rheumatoid factor or sometimes HLA-B27.

How Is It Treated?

In many ways, JRA is treated similarly to adult RA, although many drugs used to treat RA are not approved for children. Aspirin, in large doses, is generally the first line of defense in treating JRA. If the disease is progressive, your child's doctor may prescribe disease-modifying antirheumatic drugs, such as methotrexate, injectable gold or the new biologic agent etanercept (Enbrel), which was recently approved for treating JRA. Glucocorticoids, such as prednisone, are usually reserved for children with internal organ or eye inflammation because of the drugs' potential, at high doses, to stunt growth.

How Common Is It?

Juvenile rheumatoid arthritis affects an estimated 30,000 to 50,000 children in the United States. By type, 50 percent have pauciarticular JRA, 40 percent have polyarticular JRA and 10 percent have systemic onset JRA.

Other Forms Of Childhood Arthritis

Many forms of arthritis that affect adults occur less frequently in children. These include lupus, dermatomyositis and scleroderma.

A Message from the Arthritis Foundation

Juvenile arthritis awareness week is March 6-12. For more information contact your local Arthritis Foundation office. For a complimentary issue of the Kids Get Arthritis Too newsletter call 800/268-6942