Juvenile Idiopathic Arthritis (JIA)

Definition

• Juvenile Idiopathic arthritis is characterised by the presence of arthritis (swelling or effusion and >=2 of limited range of motion, tenderness, pain on motion and warmth) of one or more joints of more than 6 weeks duration in children under the age of 16 years where all other known causes have been excluded.

Incidence and classification

• The annual incidence of JIA in New Zealand is 5.1/100,000 and is classified according to the International League of Associations for Rheumatology (ILAR) criteria. Oligoarticular (47%) and polyarticular (26%) are the most common subtypes characterized by arthritis in 4 or less and 5 or more joints respectively within the first 6 months of diagnosis. Less common subtypes include enthesitis related arthritis (15%), systemic JIA (8%) and psoriatic arthritis (3%). While the incidence of JIA is significantly higher in European children (7.2/100,000), Maori and Pacific Island children are significantly more likely to present with poor prognostic features compared to European children (58% vs 27%, p=0.0001) including cervical involvement, erosive changes, joint space narrowing and rheumatoid factor positive disease. ¹.

Diagnosis

• An assessment of all joints is required to determine the presence and extent of arthritis. The PGALS (paediatric gait arms legs and spine) provides a basic structured approach to the assessment of joints in children
  A Guide to pGALS (paediatric Gait Arms Legs and Spine) | Doctor - PMM (pmmonline.org)

• If the presence of arthritis or diagnosis is uncertain then additional imaging (x-ray, USS or MRI without gadolinium) could be considered. The indication and modality may depend on age, joint type and degree of uncertainty.

• Once arthritis has been established then JIA is considered a diagnosis of exclusion. Symptoms such as associated fever, predominantly nocturnal pain (vs diurnal variation), weight loss, lymphadenopathy and hepatosplenomegaly should raise concerns regarding alternative disease including infection and malignancy. Older children with other evolving autoimmune conditions, including connective tissue disease and vasculitis, may present with arthritis.

Table 1 – The differential diagnosis of arthritis in children

Investigations

Initial investigations should exclude suspected significant alternative pathology. If osteomyelitis or septic arthritis are possible then an orthopaedic review should be considered. If other pathology has been excluded or JIA is the most likely diagnosis then few additional investigations are required but may include:

• ANA may stratify uveitis screening or be helpful if connective tissue disease is suspected.

• Full blood count and inflammatory markers (ESR and CRP) could be considered, particularly if systemic JIA and/or secondary Haemophagocytic Lymphohistiocytosis are suspected

• Rheumatoid factor and anti CCP are important prognostic markers for children with polyarticular juvenile idiopathic arthritis.

• HLA B27 should be considered in children with arthritis and enthesitis or family history suggestive of enthesitis related arthritis.

• Uveitis screening is important but do not refer for ophthalmology screening until the diagnosis has been discussed with or confirmed by a paediatric rheumatologist.
  

Management

• Initial treatment options include non steroidal anti inflammatories (NSAIDs) in the absence of any contraindications. Adjunctive pain relief could be considered including paracetamol.

Table 2 – Non steroidal anti inflammatories

• All children with suspected JIA should be discussed or referred for review with a paediatric rheumatologist within 4 weeks of review. (https://www.healthpoint.co.nz/public/rheumatology/starship-paediatric-rheumatology/).

• Treatment options considered with an established diagnosis and failure to respond to NSAIDs include targeted intra articular steroid injections depending on the type and number of affected joints. Many children with polyarticular disease will require systemic therapy with methotrexate and oral or intravenous steroid therapy.

• Children who are intolerant of methotrexate or experience a suboptimal response to monotherapy may qualify for biologic therapy (Etanercept or Adalimumab)(https://schedule.pharmac.govt.nz/ScheduleOnline.php).

• All children with confirmed JIA should be referred to an ophthalmologist. Uveitis management is determined by the primary ophthalmologist and may include topical steroid therapy with stepwise escalation of management depending on response to treatment. Additional treatment may include methotrexate and biologic therapy (Adalimumab, Infliximab).

Table 3 – Methotrexate and Biologic therapy