About JIA

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.

JIA is an autoimmune disorder where the immune system, which usually fights infection, is triggered to attack the synovium (joint lining) causing arthritis.

Genetics plays an important role in the development of JIA and several genes linked with JIA have been identified. However, arthritis is not directly inherited and it is extremely rare for more than one member of a family to be affected. Other non-genetic or environmental factors are also important. Looking at the causes of JIA continues to be an area of active research

When children develop JIA, they and their parents can often remember them falling or hurting the joint in some way.

However young children fall over and hurt themselves quite often and there is no evidence that arthritis is initiated by injury. People with arthritis often find that they experience more from pain and stiffness in cold, damp weather and we know that rapid change in temperature (both up and down) can precipitate symptoms, but there is no evidence that climate itself is a cause of arthritis. Nor is there evidence that eating particular foods causes arthritis.

Arthritis may be difficult to detect in a young child.

Often children do not complain specifically of pain but just seem unhappy or grizzly and off their food. Swelling of a joint may be difficult to detect in a plump toddler. A limp or reluctance to walk or to use both hands normally when playing may be the first sign of arthritis. When a joint is inflamed, the most comfortable position is for the joint to be bent and, if it is not regularly straightened, it may get stuck in this position. Stiffness first thing in the morning is a common feature, meaning that an affected child might find it difficult to climb out of bed or get downstairs first thing in the morning but may be able to move relatively normally later in the day.

The annual incidence of JIA is approximately 1 in 10,000 in the UK

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

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.
Systemic Onset JIA
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.
Enthesitis Related Arthritis
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).

Psoriatic Arthritis
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.
Written by: Dr Kate Martin, Consultant Paediatric Rheumatologist

Oligoarticular JIA

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.

Dr. Kate Martin, Consultant Paediatrician and Paediatric Rheumatologist, Gloucestershire Hospitals NHS Trust