Juvenile Idiopathic Arthritis Explained

Juvenile Idiopathic Arthritis is a rheumatic condition affecting youngsters, and can take many different forms.

Juvenile Idiopathic Arthritis (JIA) is defined as inflammation of one or more joints for at least six weeks in a child under the age of 16 years in whom other known causes of arthritis have been excluded. The inflamed joint is often swollen, warm, has lost normal movement and is often stiffer in the mornings. Pain is not always a major feature and thus it can be difficult for parents and 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. It 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 different subclasses described below characteristically involve different age ranges and sexes of children. 

JIA is a diagnosis of exclusion and the precise cause has not yet been identified. Needless to say this is an area of active research. The current theory is that both genetic and environmental factors are important. However, arthritis is not directly inherited and it is extremely rare for more than one member of a family to be affected.

When children develop JIA, they and their parents can often remember them falling or hurting the joint in some way, but young children fall over and hurt themŽselves 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, although it is known that certain foodstuffs such as fish oils may be of benefit in patients with adult onset rheumatoid 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.  

Oligo-articular JIA

Oligo-articular JIA is the commonest type of JIA, accounting for approximately 50% of cases in the UK. Oligo-articular arthritis, means arthritis affecting only a few (four or less) joints. If only one joint is affected, this is referred to as mono-articular arthritis. Oligo-articular disease typically affects children under the age of five years and girls more commonly than boys. The disease may be associated with inflammation in the eyes (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 will cause visual impairment. Regular examination of the eyes using a slit lamp is therefore essential for this group of children. As this disease affects only a small number of joints it is usually treated with corticosteroid injections into the involved joints and/or oral non-steroidal anti-inflammatory drugs. The prognosis is generally excellent. Seventy per cent of children will go into remission after 3 to 4 years. The remaining group progress to polyarticular disease.

Polyarticular JIA

Polyarticular JIA is defined as arthritis affecting more than four joints. This type of disease may start at any age and accounts for approximately 20% of cases in the UK. Girls are more frequently affected than boys. This type of arthriŽtis often involves the joints of the hands and feet and proŽduces pain, swelling and stiffness of the joints. 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. In addition to nonŽsteroidal anti-inflammatory drugs, disease modifying or immunosuppressive drugs are usually required to prevent serious joint damage in polyarticular disease. Only 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 seropositive polyarticular JIA or juvenile rheumaŽtoid arthritis. In these girls in particular it is important that disease modifying drugs are started early to prevent joint damage (see diagrams above).

Systemic Onset JIA

This occurs in about 10% of children with JIA and is associated with fevers that can go as high as 40C usually once a day, a rash that comes and goes and arthritis. Other areas of the body can be affected such as lymph glands can be swollen. Steroids are often needed to bring this under control together with other medications such as methotrexate

Enthesitis Related Arthritis

This is more common in older boys and not only causes arthritis but also pain at the areas where tendons insert into bones like the back of the ankle. In some this form of arthritis may continue with stiffness of the back in teenagers or older.

Psoriatic Arthritis

Arthritis can occur in people with skin psoriasis sometimes before the skin problem is seen. It can affect a few or many joints. This form of JIA can run in families as psoriasis does seem to have a genetic basis.

Written by: Dr Kate Martin, Consultant Paediatric Rheumatologist

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