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One of the most frequent chronic diseases of children and the most common rheumatological condition in this group is juvenile rheumatoid arthritis. This is not one disorder but a group of interrelated disorders which all exhibit inflammatory changes in the joints. The triggering factors for these diseases have not been uncovered and it has proven hard to delineate one particular type of condition from another due to the complex genetic factors. While it is often called JRA, there is a move to standardise the naming of these diseases into juvenile idiopathic arthritis.

The classification can be approached by describing three main subtypes, systemic onset disease where the problems are widespread, polyarticular arthritis where many joints are affected and pauciarticular where only a few joints are involved. The typical disease course is chronic with remission periods inbetween periods of flare ups, the medical treatment being typically aimed at causing remission and maintaining it over time. The biological treatment agents more recently developed have given a greatly increased effectiveness of treatments for arthritic diseases.

The triggering factors for juvenile rheumatoid arthritis have not been clearly identified, with a possible trigger of trauma or infection developing an autoimmune attack against joint tissues. The synovial lining of the joint increases in bulk and develops chronic inflammation, with perhaps some genetic vulnerability contributing to this process. A group of genes are understood to be involved in the pattern of disease presentation and the nature of its onset. There are many factors which influence the incidence of these types of arthritic diseases, such as how susceptible individuals are and the population types involved.

The oligoarticular type of juvenile chronic arthritis, in which a small number of joints are inflamed, is the commonest disease type, consisting of about half of all patients. Thirty percent have a large number of joint affected, the polyarticular type, and the rest have the systemic form. Sufferers from chronic juvenile arthritis may at some type suffer also from another autoimmune disorders. The severe pain and disability due to the arthritis causes significant psychological distress, behavioural problems, anxiety and depression. The polyarticular and oligoarticular forms occur more often in girls than boys with a frequency of three to four and a half to one. The systemic form occurs equally.

In terms of age, the few joint (oligoarticular) type occurs most commonly in children of two to four years in age, while the many joint (polyarticular) peaks at one to four years and also at six to twelve years. The systemic type can occur right through the childhood years. The division of juvenile chronic arthritis that a child belongs in is determined by the pattern of onset of the disease over the first six months. If four joints or fewer are involved then the child is classified into the oligoarticular chronic arthritis group. If a child has more than five joints affected in the six month period then they are recognised as being in the polyarticular type. The type which presents with a systemic onset comes on with the arthritis, fever and rashes.

An arthritis must occur for six weeks in a joint to be able to make the diagnosis of juvenile arthritis of the various types. Morning stiffness is a common phenomenon and relates to the fact that the joints stiffen and become more painful after being still for any length of time. The onset of the disease can be slow and gradual or very sudden, with stiffness after resting, joint pain during the day, absences from school and a limp in walking. Inflammatory bowel disease may be associated with these conditions in some cases. Children may not complain particularly about joint pain but rather they may allow a joint to become unused or limp, leading to disuse of the joint or joint contractures.

The onset of juvenile arthritis which comes on systemically is indicated by the child spiking a fever either once or twice daily with the temperature going back to normal each time. This pattern allows some diagnostic usefulness as if does not occur in the event of infections. A short lasting skin rash may also be present over the limbs and the trunk, the child may seem unwell and have joint pains in the larger body joints.