In childhood the most frequent rheumatological disease is juvenile rheumatoid arthritis which is also one of the most frequent chronic diseases in this age group. There are a number of different but related disorders which are expressed in chronic inflammation of the joints. It is not clear what causes these conditions and the complexity of the underlying genetic bases for them makes it difficult to clearly distinguish the different types. The naming of the diseases is also under review, with juvenile idiopathic arthritis perhaps gaining ground.

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 causative factors and how the arthritis develops is not clearly understood, but a trigger such as trauma or infection may start an autoimmune reaction against the joint tissues. This makes the synovial membrane lining the joint enlarge and develops a chronic inflammation, all of these things likely to occur in children who have a genetic susceptibility. Many genes are thought to be responsible for the onset of the disease and how it presents in each individual. There are wide ranges in the incidence of these conditions as the susceptibility to the disease varies along with the different population groups and exposure to environmental influences.

Approximately fifty percent of all sufferers from juvenile chronic arthritis fall into the oligoarticular type with few joints affected, making it the most common type. With a greater number of joints affected by arthritis, the polyarticular type occurs in about a third of patients, with the remaining patients having the systemic form. Juvenile arthritis patients may be susceptible to acquiring a second autoimmune disorder. The significant disability and pain causes psychological distress, problems with behaviour, depression and anxiety. Girls are more likely to suffer from the many joint affected and poor joint affected forms, with equal incidence in the systemic form.

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 type of juvenile chronic arthritis which has a system wide onset has typical symptoms of a fever which spikes regularly once or twice a day with the temperature going back towards normal in between the spikes. This is helpful diagnostically as infections do not behave in this way. A skin rash which lasts a few hours only may appear on the trunk and the limbs, the child may not be well and the larger joints may exhibit pain.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapist, back pain, orthopaedic conditions, neck pain, injury management and Physiotherapists London. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.