Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) refers to a condition affecting children and adolescents where autoimmune inflammation occurs in the joints. It is diagnosed where there is arthritis without any other cause, lasting more than 6 weeks in a patient under the age of 16. It has also been known as juvenile chronic arthritis and juvenile rheumatoid arthritis.

The key features of inflammatory arthritis are joint pain, swelling and stiffness.

There are a number of subtypes of juvenile idiopathic arthritis. Each has individual characteristics and is associated with different serology (blood tests). It is worth remembering five key subtypes:

  • Systemic JIA
  • Polyarticular JIA
  • Oligoarticular JIA
  • Enthesitis related arthritis
  • Juvenile psoriatic arthritis

 

Systemic JIA

This is also knowns as Still’s disease. This is a systemic illness that can occur throughout childhood in boys and girls. It is an idiopathic inflammatory condition. Typical features are:

  • Subtle salmon-pink rash
  • High swinging fevers
  • Enlarged lymph nodes
  • Weight loss
  • Joint inflammation and pain
  • Splenomegaly
  • Muscle pain
  • Pleuritis and pericarditis

Antinuclear antibodies and rheumatoid factors are typically negative. There will be raised inflammatory markers, with raised CRP, ESR, platelets and serum ferritin.

A key complication is macrophage activation syndrome (MAS), where there is severe activation of the immune system with a massive inflammatory response. It presents with an acutely unwell child with disseminated intravascular coagulation (DIC), anaemia, thrombocytopenia, bleeding and a non-blanching rash. It is life threatening. A key investigation finding is a low ESR.

TOM TIP: Think of Still’s disease (systemic JIA) when a patient presents with a salmon-pink rash, fevers and joint pain. In children that have fevers for more than 5 days, the key non-infective differentials to remember are Kawasaki disease, Still’s disease, rheumatic fever and leukaemia.

 

Polyarticular JIA

Polyarticular JIA involves idiopathic inflammatory arthritis in 5 joints or more. The inflammatory arthritis tends to be symmetrical and can affect the small joints of the hands and feet, as well as the large joints such as the hips and knees. There are minimal systemic symptoms, but there can be mild fever, anaemia and reduced growth. Systemic symptoms are mild, unlike systemic onset JIA.

Polyarticular JIA is the equivalent of rheumatoid arthritis in adults. Most children are negative for rheumatoid factor and are described as “seronegative”. When rheumatoid factor is positive they are described as “seropositive”. Seropositive patients tend to be older children and adolescents and the disease pattern is more similar to rheumatoid arthritis in adults.

 

Oligoarticular JIA

This is also knowns as pauciarticular JIA. It involves 4 joints or less. Usually it only affects a single joint, which is described as a monoarthritis. It tends to affect the larger joints, often the knee or ankle. It occurs more frequently in girls under the age of 6 years.

A classic associated feature with oligoarticular JIA is anterior uveitis. Patients should be referred to an ophthalmologist for management and follow up of uveitis.

Patients tend not to have any systemic symptoms and inflammatory makers will be normal or mildly elevated. Antinuclear antibodies are often positive, however rheumatoid factor is usually negative.

 

Enthesitis-Related Arthritis

Enthesitis-related arthritis is more common in male children over 6 years. It can be thought of as the paediatric version of the seronegative spondyloarthropathy group of conditions that affect adults. These conditions are ankylosing spondylitispsoriatic arthritisreactive arthritis and inflammatory bowel disease-related arthritis. Patients have inflammatory arthritis in the joints as well as enthesitis.

An enthesis (pleural: entheses) is the point at which the tendon of a muscle inserts into a bone. Enthesitis is inflammation of this insertion point. Enthesitis can be caused by traumatic stress, such as through repetitive strain during sporting activities, or can be caused by an autoimmune inflammatory process. An MRI scan of the affected joint can demonstrate enthesitis, but cannot distinguish between an enthesitis due to stress or an autoimmune process.

The majority of patients with enthesitis-related arthritis have the HLA B27 gene. This is a particular genetic variant of the human leukocyte antigen (HLA). When assessing patients for enthesitis-related arthritis, consider signs and symptoms of psoriasis (psoriatic plaques and nail pitting) and inflammatory bowel disease (intermitted diarrhoea and rectal bleeding). Patients with enthesitis-related arthritis are prone to anterior uveitis, and should see an ophthalmologist for screening, even if they are asymptomatic.

Patients with enthesitis will be tender to localised palpation of the entheses. Therefore it is worth palpating key areas to elicit tenderness of the entheses:

  • Interphalangeal joints in the hand
  • Wrist
  • Over the greater trochanter on the lateral aspect of the hip
  • Quadriceps insertion at the anterior superior iliac spine
  • Quadriceps and patella tendon insertion around the patella
  • Base of achilles, at the calcaneus
  • Metatarsal heads on the base of the foot

 

Juvenile Psoriatic Arthritis

Psoriatic arthritis is an seronegative inflammatory arthritis associated with psoriasis, the skin condition. The pattern of joint involvement varies. Patients can have a symmetrical polyarthritis affecting the small joints similar to rheumatoid, or an asymmetrical arthritis affecting the large joints in the lower limb.

Juvenile psoriatic arthritis is associated with several signs on examination:

  • Plaques of psoriasis on the skin
  • Pitting of the nails (nail pitting)
  • Onycholysis, separation of the nail from the nail bed
  • Dactylitis, inflammation of the full finger
  • Enthesitis, inflammation of the entheses, which are the points of insertion of tendons into bone

 

Management of Juvenile Idiopathic Arthritis

The management should be coordinated by a specialist in paediatric rheumatology, with a specialist multi-disciplinary team. The aim of treatment is to reduce inflammation within the joints, minimise symptoms and maximise function. 

Medical treatment depends on the severity and response, and involves:

  • NSAIDs, such as ibuprofen
  • Steroids, either oral, intramuscular or intra-artricular in oligoarthritis
  • Disease modifying anti-rheumatic drugs (DMARDs), such as methotrexate, sulfasalazine and leflunomide
  • Biologic therapy, such as the tumour necrosis factor inhibitors etanercept, infliximab and adalimumab

 

Last updated January 2020
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