Children with systemic JIA usually present with fever and a classic rash and may become quite ill. Late effects of arthritis can include joint contractures (stiff, bent joints with loss of movement) due to joint damage; limb length discrepancies and muscle wasting. Children with JIA vary in the degree to which they are affected by particular symptoms. Extra-articular
Eye disease: JIA is associated with inflammation in the front of the eye (specifically iridocyclitis, a form of chronic anterior uveitis), which affects about one in six children with JIA. Eye involvement occurs most commonly in girls, those with only a few joints involved (oligoarthritis), and those with a positive anti-nuclear antibody (ANA). It usually follows the onset of arthritis or may be detected at the same time as arthritis; occasionally it may occur before joint involvement. The factors linking eye and joint disease are not clearly understood, and the two do not necessarily follow the same course. This complication is usually asymptomatic (without symptoms) and can occur when the joints are not active. It can be detected by an experienced optometrist or ophthalmologist using a slit lamp to look for inflammatory cells in the fluid inside the eye. Most children with JIA will require referral for regular slit lamp screening examinations. Poorly controlled chronic anterior uveitis may result in permanent eye damage, including blindness.Systemic JIA: children with the Systemic JIA subtype often experience extra-articular manifestations including fever, rash, enlarged lymph nodes, enlarged liver or spleen, serositis and anaemia.
The characteristic feature of arthritis is joint swelling which is sometimes – but not always – associated with pain. The presence of joint stiffness is another typical feature, particularly when present in the morning and improving with activity.No single test can confirm a diagnosis of JIA: a combination of presenting signs and symptoms, blood tests, and if necessary medical imaging, is used to make the diagnosis. The blood tests may measure levels of inflammatory markers, as well as the presence of specific immune markers which may include anti-nuclear antibody, HLA-B27, rheumatoid factor and anti–citrullinated protein antibody. These serological markers may be negative in children with JIA, and are often present in healthy children; as such they should not be interpreted in isolation but in the context of the clinical presentation. Many children with JIA have normal blood work. X-rays may be required to ensure that the joint pain and swelling is not from a fracture, cancer, infection, or congenital abnormality. In some cases, fluid from the joint can be aspirated and analysed to assist in making a diagnosis. This test can assist by ruling out other causes of arthritis such as infection. Classification
The current classification system by the International League of Associations for Rheumatology (ILAR) recognizes seven distinct subtypes of JIA, based on their presentation within the first six months:
 Each subtype has a specific pattern of features as outlined in the table and descriptions below.