Juvenile Rheumatoid Arthritis Health Article

Definition

Juvenile rheumatoid arthritis (JRA) refers to a number of different conditions, all of which strike children, and all of which have immune-mediated joint inflammation as their major manifestation. JRA is also known as juvenile idiopathic arthritis or JIA. The European League Against Rheumatism, or EULAR, refers to the disorder as juvenile chronic arthritis, or JCA.

Description

The skeletal system of the body is made up of different types of strong, fibrous tissue known as connective tissue. Bone, cartilage, ligaments, and tendons are all forms of connective tissue that have different compositions, and thus different characteristics.

The joints are structures that hold two or more bones together. Some joints (synovial joints) allow for movement between the bones being joined (articulating bones). The simplest model of a synovial joint involves two bones, separated by a slight gap called the joint cavity. The ends of each articular bone are covered by a layer of cartilage. Both the articular bones and the joint cavity are surrounded by a tough tissue called the articular capsule. The articular capsule has two components: the fibrous membrane on the outside, and the synovial membrane (or synovium) on the inside. The fibrous membrane may include tough bands of fibrous tissue called ligaments, which are responsible for providing support to the joints. The synovial membrane has special cells and many capillaries (tiny blood vessels). This membrane produces a supply of synovial fluid that fills the joint cavity, lubricates it, and helps the articular bones move smoothly about the joint.

In JRA, the synovial membrane becomes intensely inflamed. Usually thin and delicate, the synovium becomes thick and stiff, with numerous infoldings on its surface. The membrane becomes invaded by white blood cells, which produce a variety of destructive chemicals. The cartilage along the articular surfaces of the bones may be attacked and destroyed, and the bone, articular capsule, and ligaments may begin to be worn away (eroded). These processes severely interfere with movement in the joint.

JRA specifically refers to chronic arthritic conditions that affect a child under the age of 16 years, and that last for a minimum of three to six months. JRA is often characterized by a waxing and waning course, with flares separated by periods of time during which no symptoms are noted (remission). Some literature refers to JRA as juvenile rheumatoid arthritis, although most types of JRA differ significantly from the adult disease called rheumatoid arthritis in terms of symptoms, progression, and prognosis.

Causes & symptoms

A number of different causes have been sought to explain the onset of JRA. There seems to be some genetic link, based on the fact that the tendency to develop JRA sometimes runs in particular families, and based on the fact that certain genetic markers are more frequently found in patients with JRA and other related diseases. Recent research has shown that several autoimmune diseases, including JRA, share a common genetic link. In other words, patients with JRA might share common

genes with family members who have other autoimmune diseases like rheumatoid arthritis, systemic lupus, multiple sclerosis, and others.

Many researchers have looked for some infectious cause for JRA, but no clear connection to a particular organism has ever been made. JRA is considered by some to be an autoimmune disorder. Autoimmune disorders occur when the body's immune system mistakenly identifies the body's own tissue as foreign, and attacks those tissues, as if trying to rid the body of an invader (such as a bacteria, virus, or fungi). While an autoimmune mechanism is strongly suspected, certain markers of such a mechanism (such as rheumatoid factor, often present in adults with such disorders) are rarely present in children with JRA.

Joint symptoms of arthritis may include stiffness, pain, redness, warmth of the joint, and swelling. Bone in the area of an affected joint may grow too quickly or too slowly, resulting in limbs that are of different lengths. When the child tries to avoid moving a painful joint, the muscle may begin to shorten from disuse. This is called a contracture.

Symptoms of JRA depend on the particular subtype. According to criteria published by the American College of Rheumatology (ACR) in 1973 and modified in 1977, JRA is classified by the symptoms that appear within the first six months of the disorder:

• Pauciarticular JRA: This is the most common and the least severe type of JRA, affecting about 40–60% of all JRA patients. It affects fewer than four joints, usually the knee, ankle, wrist, and/or elbow. Other more general (systemic) symptoms are usually absent, and the child's growth usually remains normal. Very few children (less than 15%) with pauciarticular JRA end up with deformed joints. Some children with this form of JRA experience painless swelling of the joint. Others have a serious inflammation of structures within the eye, which if left undiagnosed and untreated could even lead to blindness. This condition is known as uveitis, and affects about 20% of children diagnosed with JRA. While many children have cycles of flares and remissions, in some children the disease completely and permanently resolves within a few years of diagnosis.
• Polyarticular JRA: About 40% of all cases of JRA are of this type. It is most common in children up to age three or after the age of 10, and affects girls more often than boys. Polyarticular JRA affects five or more joints simultaneously. This type of JRA usually affects the small joints of both hands and both feet, although other large joints may be affected as well. Some patients with arthritis in their knees will experience a different rate of growth in each leg. Ultimately, one leg will grow longer than the other. About half of all patients with polyarticular JRA have arthritis of the spine and/or hip. Others with polyarticular JRA will have other symptoms of a systemic illness, including anemia (low red blood cell count), decreased growth rate, low appetite, low-grade fever, and a slight rash. The disease is most severe in those children who are diagnosed in early adolescence. Some of these children will test positive for a marker present in other autoimmune disorders, called rheumatoid factor (RF). RF is found in adults who have rheumatoid arthritis. Children who are positive for RF tend to have a more severe course, with a disabling form of arthritis that destroys and deforms the joints. This type of arthritis is thought to be the adult form of rheumatoid arthritis occurring at a very early age.
• Systemic onset JRA: Sometimes called Still disease (after a physician who originally described it), this type of JRA occurs in about 10–20% of all patients with JRA. Boys and girls are equally affected, and diagnosis is usually made between the ages of five and 10. The initial symptoms are not usually related to the joints. Instead, these children have high fevers; a rash; decreased appetite and weight loss; severe joint and muscle pain; swollen lymph nodes, spleen, and liver; and serious anemia. Some children experience other complications, including inflammation of the sac containing the heart (pericarditis), inflammation of the tissue lining the chest cavity and lungs (pleuritis), and inflammation of the heart muscle (myocarditis). The eye inflammation often seen in pauciarticular JRA is uncommon in systemic onset JRA. Symptoms of actual arthritis begin later in the course of systemic onset JRA, and they often involve the wrists and ankles. Many of these children continue to have periodic flares of fever and systemic symptoms throughout childhood. Some children will go on to develop a polyarticular type of JRA.
• Spondyloarthropathy: This type of JRA most commonly affects boys older than eight years of age. The arthritis occurs in the knees and ankles, moving over time to include the hips and lower spine. Inflammation of the eye may occur occasionally but usually resolves without permanent damage.
• Psoriatic JRA: This type of arthritis usually shows up in fewer than four joints, but goes on to include multiple joints (appearing similar to polyarticular JRA). Hips, back, fingers, and toes are frequently affected. A skin condition called psoriasis accompanies this type of arthritis. Children with this type of JRA often have pits or ridges in their fingernails. The arthritis usually progresses to become a serious, disabling problem.

As of 2003, there is some disagreement among specialists about the classification of JRA. Some prefer the EULAR classification, also introduced in 1977, to the ACR system. In 1997, the World Health Organization (WHO) met in Durban and issued a new classification system for JRA known as the Durban criteria, in an attempt to standardize definitions of the various subtypes of JRA. None of the various classification systems, however, are considered fully satisfactory as of early 2004.