Juvenile Idiopathic Arthritis (JIA) is a rheumatic condition affecting children and young people and can take several different forms. For at least six weeks in a child under the age of 16 years in whom other known causes of arthritis have been excluded. Inflamed joints are often swollen, warm and stiff, especially in the mornings. Pain is not always a major feature and thus it can be difficult for parents, and sometimes doctors, to detect arthritic joints.
The annual incidence of JIA (the number of new patients diagnosed as having JIA each year) is approximately 1 in 10,000 in the UK. The prevalence (the number of children known to have JIA) is about 1 in 1,000. Arthritis can start at any age from birth to adolescence, but the peak age of onset is 6 years. Both girls and boys may be affected but overall JIA is commoner in girls. The ILAR (International League of Associations for Rheumatology) Classification recognises seven different subtypes of JIA which are described below and characteristically involve different age ranges and sexes of children.
Polyarticular JIA means arthritis affecting five or more joints. This type of disease may start at any age and accounts for approximately 20% of cases of JIA in the UK. Girls are more frequently affected than boys. This type of arthritis often involves the joints of the hands and feet and produces pain, swelling and stiffness. In addition the flexor tendons of the hand may also become inflamed. Involvement of the lower limbs often results in difficulty in walking while involvement of the wrists and hands may lead to difficulties in writing and manipulative tasks. Commonly, children feel generally unwell and may have fevers when the disease is active. Disease modifying or immunosuppressive medicines or biological therapies are usually required to prevent serious joint damage in polyarticular disease. A small number of children with polyarticular disease (less than 5% of the total JIA population, often older girls) are found to be rheumatoid factor positive. This type of disease is termed rheumatoid factor positive polyarticular JIA. This is often a severe form of the disease and it is important that disease modifying drugs are started early to prevent joint damage.
Oligoarticular JIA is the commonest type of JIA, accounting for approximately 50% of cases in the UK. Oligoarticular arthritis means arthritis affecting only a few (four or less) joints. If only one joint is affected, this is referred to as monoarticular arthritis. Oligoarticular disease typically affects children under the age of five years and girls more commonly than boys. Typically parents will notice joint swelling and perhaps a limp. The disease may be associated with chronic inflammation in the eyes called chronic anterior uveitis (especially if blood tests show the presence of an antibody called antinuclear antibody or ANA). The eye disease usually does not cause obvious redness, swelling or pain, but if left untreated may cause visual impairment. Regular examination of the eyes using a slit lamp is therefore essential for this group of children. As oligoarticular JIA affects only a small number of joints it is usually treated with corticosteroid injections directly into the involved joints. The prognosis is generally good, but a proportion of children with oligoarticular disease do develop arthritis affecting more than four joints over time (extended oligoarticular JIA) and this usually requires further treatment.
This occurs in about 10% of children with JIA and may occur at any age. Characteristic features are spiking fevers that can go as high as 40°C, usually once a day, and a rash that comes and goes, often appearing with the fevers. Other areas of the body can be affected such as lymph glands, which may be swollen and there may be inflammation around the heart (pericarditis) or lungs (pleuritis). Arthritis may be present at the beginning of the disease or develop later. Steroids are often needed to bring this under control.
This is more common in older boys, usually over 8 years of age, and not only causes arthritis, usually in the large joints of the legs, but also pain at the areas where tendons insert into bones such as behind or under the heel (enthesitis). In this disease inflammation of the eye may produce redness and soreness of the eyes (acute anterior uveitis). Most young people with this type of arthritis are positive for a particular genetic test called HLA B27. In some young people this form of arthritis resolves in childhood but in others it may progress to involve the sacroiliac joints (lower back) and spine (spondyloarthropathy).
This type of arthritis occurs in children or young people with psoriasis (a scaling skin rash) or in those with first degree family members (a parent or sibling) with psoriasis. It may sometimes develop before the skin problem is seen or has been identified. It can affect a few or many joints and is quite variable in its prognosis.
Dr. Kate Martin, Consultant Paediatrician and Paediatric Rheumatologist, Gloucestershire Hospitals NHS Trust