The cause or causes of Juvenile Idiopathic Arthritis (JIA) are not fully understood. The definition of idiopathic is a condition that develops without a known cause. What is known about JIA is that it is a group of autoimmune disorders and that at least 2 factors are believed to be involved in the development of these diseases.

Body’s Immune System
The immune system defends the body against “aliens”: bacteria, viruses, toxins, and other harmful foreign substances. When it recognizes one of these invaders, it triggers an inflammatory response, which normally helps in healing infections, injuries, and wounds. However, in diseases like JIA, the immune system somehow mistakes normal cells and tissues for “foreigners” and attacks them, resulting in joint inflammation—pain, heat, redness, and swelling.

Two types of white blood cells (T cells and B cells) play a role in juvenile idiopathic arthritis. T cells release cytokines (chemicals involved in the inflammatory response) and cause B cells to release antibodies (immune proteins), resulting in inflammation. Scientists have not established why the immune system goes haywire in children with JIA, but current thought indicates that a combination of genetics and other factors trigger the development of the disease.

Genetics
Certain genetic markers (ie, genes) are believed to play a role in juvenile idiopathic arthritis. Although they don’t cause JIA, children with those markers have a predisposition for getting the disease. The presence of those markers does not mean a child has or will get JIA.

A study supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases recently discovered 14 genes involved in JIA and confirmed 3 others that had previously been identified. Furthermore, the study indicated that an additional 11 genetic regions could be involved in the development of juvenile idiopathic arthritis. But that’s not the whole story: another factor seems to be needed to trigger the disease.

Other Factors
Researchers believe that viral or bacterial infections can be that trigger. If the child has a genetic marker linked to JIA, an infection could “push the button” on that marker and jump-start the immune system into “attack mode.” So far, though, no single bacterium or virus has been singled out. Environmental factors such as foods, allergies, and toxins have been suggested, none has yet been identified yet.

Juvenile Idiopathic Arthritis Diagnosis
It is important for your child to get an accurate diagnosis. This process can take some time (and patience). A careful physical examination and history are needed. Tests can help confirm or rule out certain things, but there is no single test that can diagnose juvenile idiopathic arthritis. A diagnosis of JIA is made only if the symptoms started before age 16 and if the symptoms have been present for at least 6 weeks.

Medical History
The doctor will ask you and your child several questions, such as:

• When did symptoms start?
• Does anyone in your family have an autoimmune disease?

Assessment of Symptoms

• Which joints are affected?
• Has your child been limping?
• Is your child hesitant to use an arm or a leg?
• Has your child shown any problems with fine motor skills?
• Are the joints stiff after he/she wakes up or after a period of rest?
• Does your child have less energy than usual, or have you noticed that he/she has become less active?
• Has your child been running a fever?
• Do the symptoms get worse or better at times?

Physical Examination
The doctor will assess your child’s overall health and for specific signs and symptoms of juvenile idiopathic arthritis, such as:

• Joint swelling, pain, and stiffness
• Swollen lymph nodes
• Rash(es)
• Inflammation (of organs)

Laboratory Tests
Blood tests cannot provide a definitive diagnosis of JIA, but they can help confirm a diagnosis based on the above assessments, as well as identify the particular type of juvenile idiopathic arthritis. They can also rule out other conditions that may resemble JIA, such as Lyme disease and lupus.

• Erythrocyte sedimentation rate (ESR or sed rate). In inflammatory conditions such as juvenile idiopathic arthritis, erythrocytes (red blood cells) fall more quickly to the bottom of the tube; the test measures how fast they fall. The ESR is elevated in most inflammatory conditions.
• Antinuclear antibodies (ANAs). ANAs–autoantibodies that target substances in the nuclei (center) of the cells–are present in some children with JIA.
• Rheumatoid factor (RF). RF is a group of antibodies normally present in the joint lining. In adults, high levels of RF are a better indication of rheumatoid arthritis. In children, however, the presence of RF is not typical, but it can help differentiate certain types of JIA.
• Anticyclic citrullinated peptide (CCP) antibodies. Antibodies to CRP can be present in the blood even years before JIA is clinically evident. This test also assesses inflammation.

Other laboratory tests may be needed to confirm or rule out a diagnosis of JIA.

X-rays and Imaging Tests
Although x-rays are not usually diagnostic for JIA, your doctor may want to check for joint injury or bone abnormality. Although damage to cartilage can be evident in the early stages, x-rays are more valuable in showing bone damage as the disease progresses.

Other imaging tests may be ordered as well. The most valuable tool for diagnosing JIA is a thorough examination and assessment.