Related concepts:

Juvenile rheumatoid arthritis, JRA

Introduction to arthritis:

When most people think of arthritis, they think of a disease common in old people, but Juvenile Rheumatoid Arthritis (JRA) is a group of diseases that strikes the young.

What is arthritis?

JRA refers to a grab bag of at least five distinct arthritis diseases with at least seven patterns of illness. They can range from relatively mild conditions that disappear at puberty, to relentlessly progressive, crippling arthritis.

The exact cause of the arthritides in JRA remains unknown. The two leading theories are that the diseases are caused by infections with as-yet-unidentified microorganisms, or that the diseases are the result of an over-exuberant autoimmune reaction -- one's own immune system turning against oneself.

Who gets arthritis?

Some children inherit a genetic predisposition to JRA.

As stated earlier, there are at least five major subtypes of rheumatic disease that fall under the name JRA. Two forms of the disease are considered polyarticular (many-joint) rheumatoid arthritis. The great majority of children affected by this sub-type of JRA are girls.

The polyarticular diseases account for about 35 percent of children with JRA. The two forms of the polyarticular disease are differentiated by a blood test for an immune compound called the rheumatoid factor. Rheumatoid Factor Positive Polyarticular Disease tends to appear in late childhood. Rheumatoid Factor Negative Polyarticular JRA may begin at any time in childhood.

The next group of diseases are called pauciarticular (few-joints) diseases. There are two pauciarticular types of JRA. Pauciarticular Disease Type 1 is the single most common form of JRA; it accounts for 30 to 40 percent of children with JRA. Pauciarticular Type 1 appears typically in girls and usually begins before the fourth birthday. Pauciarticular Type 2 accounts for 10 to 15 percent of patients with JRA and appears predominantly in boys. It usually begins after the age of eight.

The fifth type of JRA is called Systemic JRA. This accounts for 10 to 20 percent of children with JRA and affects boys and girls equally.

What are the symptoms of arthritis?

All forms of rheumatoid arthritis are characterized by chronic swelling and inflammation of the synovial membrane that lines the joints. If this chronic inflammation continues over many years, the joint cartilage and joint bone become eroded and are gradually destroyed. The amount of time the chronic inflammation can last before the damage becomes permanent varies a great deal, but it is a much longer period in Juvenile Rheumatoid Arthritis compared to Adult Rheumatoid Arthritis. Many children with JRA outgrow the disease and never develop permanent joint damage.

The polyarticular diseases are characterized by involvement of multiple joints, typically including the small joints of the hands. Rheumatoid Factor Positive Polyarticular Disease tends to be the more severe of the two polyarticular diseases. Rheumatoid nodules often appear at the joints. Rheumatoid Factor Negative Polyarticular JRA is typically mild. It is rarely associated with rheumatoid nodules at the joint spaces.