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.

Juvenile idiopathic arthritis can be classified into three main types, one which affects a few joints (pauciarticular arthritis), one which affects many joints (polyarticular arthritis) and a more overall disease which is termed systemic juvenile arthritis. The disease is chronic, persisting over a long period with flare ups and then periods of remission, with treatments aimed at inducing remissions for as long as possible without toxic effects from medication. More recent biological treatment agents have greatly increased the treatment efficacy against many 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.

Around half of all sufferers from juvenile chronic arthritis have the oligoarticular or pauciarticular type where a small number of joints are affected, around a third have the polyarticular type with many joints affected and the remainder have the more systemic type. People suffering from juvenile chronic arthritis may develop other autoimmune disorders. Psychological side-effects are common due to the pain and functional problems which occur with this disease, causing depression, anxiety and behaviour problems. The few joint and many joint forms of the disease occur more commonly in girls at a ratio of 3 to 4.5 to one with the systemic type occurring equally in boys and girls.

The polyarticular or many affected joint form of arthritis has two peaks of incidence, one covering one to four years of age and another covering six to twelve years. The fewer joint type, the oligoarticular form, tends to occur in children who are two to four years old. The systemic type has no particular age of incidence. The disease pattern over the first six months determines which pattern the individual patient fits into. If four or fewer joints are affected during this period then the diagnosis is the oligoarticular or fewer joint group. More than five joints are symptomatic during the first six months this indicates the polyarticular or many joint diagnosis. Arthritis, rashes and a fever are the typical onset symptoms of the systemic form.

A six week period of arthritis in a joint is necessary for a diagnosis to be made of one of the forms of juvenile arthritis. Typically there is a complaint of morning stiffness and stiffness after other periods of the joint having been kept still for a while. Disease onset can be insidious, i.e. slow and sneaky, or very abrupt with all the symptoms coming on in a short space of time. These can include joint stiffness after immobility, pain in the joints during the day, limping and school absences, with in some cases the addition of inflammatory disease of the bowel. There may be few complaints from the child of pain in their joints, instead they may just stop using a joint with the consequent contracture or disuse atrophy.

In the systemic form of juvenile arthritis the child suffers from fevers which spike once or twice a day at around the same time, the temperature typically returning back to normal each time. This pattern is different from infections so helps to distinguish what the patient is suffering from. These patients usually show a short lasting rash over the trunk and limbs, joint pain often in the bigger joints and appear to be unwell.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapy, 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.