Juvenile idiopathic arthritis

Podiatry Now, August, 2009 by Matthew Malone

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Juvenile idiopathic arthritis (JIA) is an umbrella name for a vast range of disorders in which the hallmark symptoms are persistent inflammation of joints. (1) This group of diseases is both clinically and genetically distinct from rheumatoid arthritis in adults. (2) In 1997, and more recently in 2001, the International League of Associations for Rheumatology (ILAR) (3) created common standards for the evaluation of paediatric rheumatology. No longer were the names juvenile rheumatoid arthritis, juvenile chronic arthritis and Stills disease used to describe a child with an inflammatory process.

Currently around 1 in 1000 children present with JIA, amounting to over 12,000 children affected each year in the UK. (4) According to the ILAR, to be diagnosed with JIA a child must present younger than 16 years of age, with an arthritis onset lasting longer than 6 weeks, with morning stiffness lasting longer than half an hour and complaining of joint pain. The ILAR provides classifications for a child with JIA, depending on their presentation (Tables 1 & 2).

Scientists are still waiting to confirm the true aetiology of JIA. The current theories lie around an immune-mediated response comprising of T-cells and B-cells, which are thought to interact with HLA alleles to create an immune response by activating macrophages to release cytokines. (5) Cytokines are small proteins secreted by macrophages that regulate and mediate immunity and inflammation; they exist in two forms--either pro-inflammatory or anti-inflammatory (Table 3). (6)

Complex genetic traits and environmental triggers have also been implicated in the disease process. Reports of children who have had the rubella immunisation and then going onto develop JIA have been highlighted (7) and chlamydia has also been identified in the joints of some children with JIA. (8).

Clinical features

The inflammatory process that occurs in children with JIA is often unpredictable, and periods of remissions and flare-ups occur frequently. The major effect JIA has on the skeletal system is the chronic inflammation to synovial joints. In the lower limb, for example, a persistent inflammatory response in the knee results in the formation of pannus, causing both joint effusion and then joint destruction (Figure 1) (9) along with joint pain and often a reduced range of motion. (10,11) Other non-specific inherent symptoms such as lethargy, fever, poor appetite and irritability may also predominate. (12)

Pain is a major symptom of childhood arthritis, and in one study 86% of children with JIA reported symptoms of pain. (13) Lovell & Walco (14) also indicated that 60% of their patients highlighted pain at the disease onset and 50% a year later.

Where chronic inflammation is present for prolonged periods, for example at the knee, then it can bring about the rapid growth and enlargement of the adjacent long bones epiphyseal plates, thus lengthening the limb overall (Figure 2). This is prevalent in poly-articular JIA. The overgrowth is often asymmetrical and has a predilection for the medial aspect of the tibial / femoral epiphysis, which also creates a valgus deformity. (15) The increased growth phase in the child is sometimes only short lived and the overall effect that pro-inflammatory mediators have can lead to a premature fusion of the epiphysis leading to a shortened limb in the long run (16).

This overgrowth phenomenon may also occur at the ankle joint (distal tibial / fibular epiphysis), again creating a valgus deformity. Abnormal modelling and shaping of the talus can cause both a limitation and function at the ankle joint, whilst any other joint articulation in the foot maybe prone to damage, particularly the subtalar joint (STJ).

If this occurs then a varus or valgus deformity of the hind-foot maybe seen. (17) In a study by Spraul & Koenning, 144 children with JIA presented with foot problems including inflammation, limitation and malalignment; 94% of the subjects had one or more foot problems, with 73% having a pronated rear-foot and mid-foot. (17)

The hip is also prone to overgrowth and deformity, often a shortening of the femoral neck, and persistent anteversion can be seen. (18,19)

Further reports of children with JIA being predisposed to osteopenia have been highlighted in past research. Osteopenia results as a decrease in bone mineral density can occur with the long-term use of steroid treatment. (20,21) Studies that have looked at prolonged periods of immobility, which is often see in JIA patients, found that the lack of physical exertion leads to a decreased mechanical (effects of muscle contraction and force) stress on the bone. This lack of mechanical stress appears to increase bone resorption without a reciprocal increase in osteoblastic activity, (22) resulting in a decreased bone mineral density.

Exercise in general seems to play an integral role in managing active inflammatory joints and maintaining a healthy muscular system. Studies that have looked at periods of reduced physical activity have shown that muscle atrophy will occur, (23) along with a reduction in muscle strength, localised atrophy and weakness all noted in the muscles located close to active joint synovitis. (24-26) This can frequently be seen around the knee, with a wasting of the quadriceps muscle group (see Figure 3).