The major types of onset are described according to presentation during first the 6 months of the disease.
- Pauciarticular / Oligoarticular (Few joints) It is the most frequent variety (seen in 50% cases). It affects only a few joints, fewer than 5. The large joints, such as the knee, hip, shoulder and elbow are most likely to be affected; however, the small joints may escape. This type of JIA is most common in children (usually girls) younger than 8 years. Children who develop this disease have a 20-30% chance of developing inflammatory eye problems and need frequent eye examinations. It is further subdivided into a).Persistent (where the no of joints remain the same throughout the course of the disease and b) Extended Oligoarthritis where the disease starts with less than /equal to 4 joints and keeps adding up more joints after the initial 6 months.
- Polyarticular (many joints) It is seen in about 30% of cases of JRA. It affects 5 joints or more within 6 months of onset. The small joints such as those in the hands and feet are most likely to be affected. This type can begin at any age. This group is further sub divided into 1) Rheumatoid factor positive (RF positive poly JIA ) and 2) RF negative poly JIA. The former has a course similar to adult RA.
- Systemic onset JIA (SOJIA) Seen in 20% of cases and more common in boys, this disease affects many systems of the body. Children may have high fevers, skin rashes, and problems caused by inflammation of the internal organs such as the heart, lung, liver and spleen and other parts of the digestive tract. It is sometimes called "Adolescent-Onset Still's Disease.” The systemic features precede the onset of joint symptoms in many cases.
- Psoriatic arthritis: This group may be associated with the presence of either oligo/poly articular involvement, more specifically Dactylitis along with a family history of psoriasis. 20% of children may have certain antibodies which make them prone to eye inflammation.
- Enthesitis related arthritis (ERA) This type is more common in boys more than 10 years of age and often test positive for a genetic test HLA B27. This overlaps with the group juvenile spondyloarthritides.