Juvenile arthritis (JA) refers to a number of different conditions, all of which strike children, and all of which have joint inflammation as their majormanifestation.
The skeletal system of the body is made up of different types of the strong,fibrous tissue known as connective tissue. Bone, cartilage, ligaments, and tendons are all forms of connective tissue which 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 (called 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 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, andthe synovial membrane (or synovium) on the inside. The fibrous membrane mayinclude tough bands of fibrous tissue called ligaments, which are responsiblefor providing support to the joints. The synovial membrane has special cellsand many capillaries (tiny blood vessels). This membrane produces a supply of synovial fluid which fills the joint cavity, lubricates it, and helps the articular bones move smoothly about the joint.
In JA, the synovial membrane becomes intensely inflamed. Usually thin and delicate, the synovium becomes thick and stiff, with numerous infoldings on itssurface. 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.
JA specifically refers to chronic arthritic conditions which affect a child under the age of 16 years, and which last for a minimum of three to six months. JA 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 JA as juvenile rheumatoid arthritis, although most typesof JA differ significantly from the adult disease called rheumatoid arthritis, in terms of symptoms, progression, and prognosis.
A number of different causes have been sought to explain the onset of JA. There seems to be some genetic link, based on the fact that the tendency to develop JA sometimes runs in a particular family, and based on the fact that certain genetic markers are more frequently found in patients with JA and other related diseases. Many researchers have looked for some infectious cause for JA, but no clear connection to a particular organism has ever been made. JA isconsidered by some to be an autoimmune disorder. Autoimmune disorders occurwhen the body's immune system mistakenly identifies the body's own tissue as foreign, and goes about attacking 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 JA.
Joint symptoms of arthritis may include stiffness, pain, redness and warmth of the joint, and swelling. Bone in the area of an affected joint may grow tooquickly, or too slowly, resulting in limbs which are of different lengths. When the child tries to avoid moving a painful joint, the muscle may begin toshorten from disuse. This is called a contracture.
Symptoms of JA depend on the particular subtype. JA is classified by the symptoms which appear within the first six months of the disorder:
- Pauciarticular JA: This is the most common and the least severe type of JA, affecting about 40-60% of all JA patients. This type of JA 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 JA end up with deformed joints. Some children with this form of JA experience painless swellingof the joint. Some children with JA have a serious inflammation of structures within the eye, which if left undiagnosed and untreated could even lead toblindness. While many children have cycles of flares and remissions, in somechildren the disease completely and permanently resolves within a few years of diagnosis.
- Polyarticular JA: About 40% of all cases of JA are of this type. More girls than boys are diagnosed with this form of JA. This type of JA is most common in children up to age three, or after the age of 10. Polyarticular JA affects five or more joints simultaneously. This type of JA 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 kneeswill experience a different rate of growth in each leg. Ultimately, one legwill grow longer than the other. About half of all patients with polyarticular JA have arthritis of the spine and/or hip. Some patients with polyarticularJA will have other symptoms of a systemic illness, including anemia (low redblood cell count), decreased growth rate, low appetite, low-grade fever, anda 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 isfound in adults who have rheumatoid arthritis. Children who are positive forRF tend to have a more severe course, with a disabling form of arthritis which 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 JA: Sometimes called Still disease (after a physician who originally described it), this type of JA occurs in about 10-20% off all patientswith JA. Boys and girls are equally affected, and diagnosis is usually madebetween the ages of 5-10 years. The initial symptoms are not usually relatedto 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 inflammationoften seen in pauciarticular JA is uncommon in systemic onset JA. Symptoms ofactual arthritis begin later in the course of systemic onset JA, 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 JA.
- Spondyloarthropathy: This type of JA most commonly affects boys older than eight years of age. The arthritis occurs in the knees and ankles, moving over time to includethe hips and lower spine. Inflammation of the eye may occur occasionally, butusually resolves without permanent damage.
- Psoriatic JA: This type of arthritis usually shows up in fewer than four joints, but goes on to include multiple joints (appearing similar to polyarticular JA). Hips, back, fingers, and toes are frequently affected. A skin condition called psoriasis accompanies this type of arthritis. Children with this type of JA often have pits or ridges in their fingernails. The arthritis usually progresses to become a serious, disabling problem.
Diagnosis of JA is often made on the basis of the child's collection of symptoms. Laboratory tests often show normal results. Some nonspecific indicatorsof inflammation may be elevated, including white blood cell count, erythrocyte sedimentation rate, and a marker called C-reactive protein. As with any chronic disease, anemia may be noted. Children with an extraordinarily early onset of the adult type of rheumatoid arthritis will have a positive test for rheumatoid factor.
Treating JA involves efforts to decrease the amount of inflammation, in orderto preserve movement. Medications which can be used for this include nonsteroidal anti-inflammatory drugs (such as ibuprofen and naproxen). Oral (by mouth) steroid medications are effective, but have many serious side effects with long-term use. Injections of steroids into an affected joint can be helpful. Steroid eye drops are used to treat eye inflammation. Other drugs which have been used to treat JA include methotrexate, sulfasalazine, penicillamine, and hydroxychloroquine. Physical therapy and exercises are oftenrecommended in order to improve joint mobility and to strengthen supporting muscles. Occasionally, splints are used to rest painful joints and to try to prevent or improve deformities.
The prognosis for pauciarticular JA is quite good, as is the prognosis for spondyloarthropathy. Polyarticular JA carries a slightly worse prognosis. RF-positive polyarticular JA carries a difficult prognosis, often with progressive, destructive arthritis and joint deformities. Systemic onset JA has a variable prognosis, depending on the organ systems affected, and the progression topolyarticular JA. About 1-5% of all JA patients die of such complications asinfection, inflammation of the heart, or kidney disease.
Because so little is known about what causes JA, there are no recommendationsavailable for how to avoid developing it.