Oligoarticular JIA (oligo-JIA) is the most common form of JIA, and involves arthritis in four or fewer joints.
Approximately 60% of patients with JIA have this form of chronic arthritis.
Girls are affected more frequently than boys.
Patients with oligo-JIA are at risk of developing an inflammatory eye disease called uveitis.
Children with uveitis (yoo-vee-eye-tis) frequently do not complain of anything, and therefore requiring regular eye (slit lamp) exams.
The patients at greatest risk are young children, early in their diagnosis with a positive ANA blood test.
There is also subset of oligo-JIA patients that progress to have arthritis involving more than five joints, called extended oligo-JIA.
Polyarticular Juvenile Idiopathic Arthritis (Poly-JIA) is a less common subset of JIA, which involves arthritis in many (five or more) joints, often with finger involvement.
Although young children may also have this form of arthritis, teenagers with poly-JIA and a positive rheumatoid factor blood test have an arthritis that resembles adult rheumatoid arthritis.
Poly-JIA is a very intense arthritis that requires the use of medicines, such as Disease-Modifying-Anti-Rheumatic-Drugs (DMARDs) or biologics in order to treat the arthritis and prevent joint damage, deformity and disability.
Many children may have other symptoms related to their arthritis, such as morning stiffness, fatigue, poor appetite (with possible weight loss) and anemia.
These children may also have blood tests that reveal inflammation, with elevated inflammatory markers, such as an ESR or CRP.
Systemic Onset Juvenile Idiopathic Arthritis (So-JIA) is another subtype of JIA affecting 10% of children with JIA.
It is characterized by the presence of high daily fevers, a “salmon-colored” rash that is usually worse with fever, and arthritis. Sometimes the arthritis is not initially present when the children have fever and rash.
Children with So-JIA are often quite ill, with weight loss, enlarged lymph nodes and anemia. Some children may develop effusions (fluid) around their heart and lungs, liver disease, which may rarely progress to potentially life-threatening disease with severe bleeding, as well as brain and bone marrow malfunctioning.
Many children with So-JIA require steroids to control their disease in addition to DMARDs and biologics.
Psoriatic Arthritis is another subtype of JIA in which a child has chronic arthritis and a skin rash called psoriasis, which often looks like a dry, silvery, scaly rash.
There may not be psoriasis at the time the arthritis is diagnosed, but there may be a strong family history of psoriasis.
Another subtype of JIA is Enthesitis-related arthritis, which may also be called Spondyloarthropathy.
In addition to chronic arthritis, these children have enthesitis, which is inflammation of structures, such as ligaments, around the joints, which may cause pain.
Many of these patients may also have arthritis of the back and neck, as well as morning stiffness.
Some children with Enthesitis-related Arthritis may also develop inflammation of their gastrointestinal system.