Arthritis involves inflammation of the joints that causes pain and swelling. Although many people believe arthritis is a disease of old age, various forms of arthritis can affect just about anyone at any age. When arthritis occurs in children younger than age 16, it is called juvenile arthritis. Approximately 285,000 children in the United States have some form of the disease.
The most common forms of juvenile arthritis are:
Juvenile rheumatoid arthritis, also called juvenile idiopathic arthritis – This is the most common form of juvenile arthritis. Juvenile rheumatoid arthritis is thought to be an autoimmune disease, which means that, for unknown reasons, the body's immune system attacks some of its own tissue the same way it would react against a foreign invader such as a virus or bacteria. In juvenile rheumatoid arthritis, the lining of the joint (called synovial membrane) becomes inflamed and enlarged, limiting movement and causing pain and tenderness. Enzymes released by the inflamed membranes cause further damage by eroding the bone and cartilage. This type of joint and bone damage can cause problems in a growing child. If the growth areas of the bones are affected, the bones may grow at different rates so that one bone may develop abnormally in shape or size. The result could be, for example, that one leg might be permanently shorter than the other.
There are several subcategories of juvenile rheumatoid arthritis, including:
Systemic onset type, which begins with a whole-body (systemic) reaction, including high fevers; skin rash on the legs, arms and trunk; joint inflammation; and signs of inflammation of other body organs, such as enlarged lymph nodes or lining of the lungs (pleurisy). A child may have one or more episodes of systemic onset juvenile rheumatoid arthritis that eventually disappears, or the condition may persist into adulthood.
Pauciarticular onset disease, in which fewer than five joints are affected, is the most common form of juvenile rheumatoid arthritis. The large joints – such as knees, elbows, and ankles – are often affected, but usually not the same joints on both sides of the body. For example, the knee on one side may be affected and the ankle on the other. Symptoms include pain, swelling, stiffness, redness and warmth at the affected joint. Children with this type of juvenile rheumatoid arthritis are particularly susceptible to an eye inflammation called iridocyclitis. These children need to be evaluated often by an ophthalmologist, perhaps as often as every three months, because there may not be any symptoms and permanent eye damage can occur even if other symptoms of juvenile rheumatoid arthritis are under control. Treatment for iridocyclitis is highly effective. Many or even most children with pauciarticular onset juvenile rheumatoid arthritis will notice that the disease subsides over time.
Polyarticular disease, in which five or more joints are affected, usually involves the small joints, such as those in fingers and toes, although large joints can also be affected. Symptoms include the same inflammatory symptoms as other types of juvenile rheumatoid arthritis, along with low-grade fever and bumps called rheumatoid nodules near the affected joints. Typically, the same joints on both sides of the body are affected. Polyarticular juvenile rheumatoid arthritis is more common in girls than in boys, is usually more severe than the other two types, and often leads to long-term joint problems. In 5% to 10% of cases, the antibody called rheumatoid factor can be detected in a blood test, which further classifies the juvenile rheumatoid arthritis as seropositive. Seropositive juvenile rheumatoid arthritis is most like adult rheumatoid arthritis, and often continues into adulthood.
Juvenile axial spondylo arthritis – This disease involves the large joints of the lower body, particularly the lower back and hips. Key symptoms are lower back pain or stiffness, especially in the morning. The pain improves with exercise. It affects boys more often than girls.
Reactive arthritis (formerly called Reiter's syndrome) – This type of arthritis can develop weeks to months after a child has been exposed to certain bacteria, in particular shigella, salmonella or yersinia associated with diarrhea. The disease usually starts suddenly. Key symptoms are fever along with pain and inflammation in several joints, conjunctivitis (eye inflammation) and painful urination.
Juvenile psoriatic arthritis – This type of chronic arthritis strikes some children who have psoriasis, and seems to have a genetic component. Along with joint pain and inflammation, key symptoms are pitted fingernails, psoriasis and a raised, scaly rash behind the ears, in the area of the navel, along the scalp or other body areas.
Juvenile systemic lupus erythematosus (lupus) – Although lupus usually does not appear before adolescence, when it occurs in children it is very similar to lupus in adults. This disease can cause inflammation and tissue damage in many areas of the body, especially the skin, joints, blood vessels, brain, heart, muscles or kidneys. The disease often appears in episodes that come and go for no particular reason. Key symptoms include a rash on the cheeks, sensitivity to sunlight, mouth or nose sores, joint pain, seizures or other signs of neurological problems, and chest pain.