Juvenile arthritis is a disease in which there is inflammation (swelling) of the synovium in children aged 16 or younger. The synovium is the tissue that lines the inside of joints.
Juvenile arthritis is an autoimmune disease. That means the immune system, which normally protects the body from foreign substances, attacks the body instead. The disease is also idiopathic, which means that no exact cause is known. Researchers believe juvenile arthritis may be related to genetics, certain infections, and environmental triggers.
Juvenile rheumatoid arthritis (JRA) is a childhood disease that affects the joints. There are several different types of JRA, but systemic-onset juvenile rheumatoid arthritis is the rarest form, accounting for just 10%-20% of all JRA cases.
Systemic-onset JRA causes high, spiking fevers, rash, and joint aches. The word "systemic" means that it affects the entire body. Systemic-onset JRA usually begins when a child is between 5 and 10 years old, and it affects boys and girls equally.
What are the different types of juvenile arthritis?
There are five types of juvenile arthritis:
Systemic arthritis, also called Still's disease, can affect the entire body or involve many systems of the body. Systemic juvenile arthritis usually causes high fever and a rash. The rash is usually on the trunk, arms, and legs. Systemic juvenile arthritis can also affect internal organs, such as the heart, liver, spleen, and lymph nodes, but usually not the eyes. Boys and girls are equally affected.
Oligoarthritis, also called pauciarticular juvenile rheumatoid arthritis, affects fewer than five joints in the first six months that the child has the disease. The joints most commonly affected are the knee, ankle, and wrist. Oligoarthritis can affect the eye, most often the iris. This is known as uveitis, iridocyclitis, or iritis. This type of arthritis is more common in girls than in boys, and many children will outgrow this disease by the time they become adults.
Polyarthritis, also called polyarticular arthritis, involves five or more joints in the first six months of the disease -- often the same joints on each side of the body. This type of arthritis can affect the joints in the jaw and neck as well as those in the hands and feet. This type also is also more common in girls than in boys and more closely resembles the adult form.
Psoriatic arthritis affects children who have both arthritis and the skin disorder psoriasis. The child might get either the psoriasis or the arthritis years before developing the other part of the disease. Children with this type of arthritis often have pitted fingernails.
Enthesitis-related arthritis is a type of arthritis that often afflicts the spine, hips, eyes, and entheses (the places where tendons attach to bones). This type of arthritis occurs mainly in boys older than 8 years of age. There is often a family history of arthritis of the back (called ankylosing spondylitis) among the child's male relatives.