Oligoarticular (or pauciarticular) JIA affects 4 or fewer joints in the first 6 months of illness.Patients with oligoarticular JIA are more often ANA positive, when compared to other types of JIA.Accounts for about 50% of JIA cases. Usually involves the knees, ankles, and elbows but smaller joints such as the fingers and toes may also be affected. The hip is not affected unlike polyarticular JIA. It is usually not symmetrical, meaning the affected joints are on one side of the body rather than on both sides simultaneously.
Polyarticular JIA affects 5 or more joints in the first 6 months of disease. This subtype can include the neck and jaw as well as the small joints usually affected. This type of JIA is more common in girls than in boys. Usually the smaller joints are affected in polyarticular JIA, such as the fingers and hands, although weight-bearing joints such as the knees, hips, and ankles may also be affected.
Systemic JIA is characterized by arthritis, fever and a salmon pink rash.Systemic JIA can be challenging to diagnose because the fever and rash come and go.It affects males and females equally, unlike the other two subtypes of JIA.Systemic JIA may have internal organ involvement and lead to serositis (e.g. pericarditis).It is also known as "systemic onset juvenile rheumatoid arthritis".It is sometimes called "adolescent-onset Still's disease", to distinguish it from adult-onset Still's disease. However, there is some evidence that the two conditions are closely related.
Symptoms of JIA are often non-specific initially, and include lethargy, reduced physical activity, and poor appetite.The first manifestation, particularly in young children, may be limping. Children may also become quite ill, presenting with flu-like symptoms that persist. The cardinal clinical feature is persistent swelling of the affected joint(s), which commonly include the knee, ankle, wrist and small joints of the hands and feet. Swelling may be difficult to detect clinically, especially for joints such as those of the spine, sacroiliac joints, shoulder, hip and jaw, where imaging techniques such as ultrasound or MRI are very useful.
Pain is an important feature of JIA, but young children may have difficulty in communicating this symptom. Morning stiffness that improves later in the day is a common feature. Late effects of arthritis include joint contracture (stiff, bent joint) and joint damage. Children with JIA vary in the degree to which they are affected by particular symptoms.