Juvenile Idiopathic Arthritis

Definition:
It is defined as a persistent arthritis of unknown aetiology that begins before 16 years of age and persists for a least six weeks.

Aetiology:
Its cause is unknown but it is assumed that environmental factors especially viral aetiology act as a trigger in a genetically susceptible individuals.
However, it is unusual for more than one child in a family to have arthritis.

Differential diagnosis:

• Septic arthritis
• Truamatic
• Post-infectious or reactive arthritis
• Rheumatic fever
• Acute lymphoblastic leukaemia/ Bone tumour
• Osteomyelitis

Classification:
Juvenile idiopathic arthritis can be classified into seven subtypes:
• Oligoarticular - four or fewer joints and is the most common subtype.
• Polyarticular - five or more joints are involoved.
rheumatoid factor positive
rheumatoid factor negative
• Systemic - associated with high spiking fever, erythematous rash, lymphadenopathy and hepatosplenomegaly.
• Enthesitis related arthritis - associated with enthesitis or with lower axial skeletal involvement. Human leukocyte antigen (HLA) B27 is present or there is a family history of a first-degree relative with a HLA B27-related disease. A significant
proportion of patients will develop sacroiliitis as adults, but back and sacroiliac joint involvement is uncommon during childhood.
• Psoriatic - assoicated with asymmetrical involvement of small and large joints, and either the development of psoriasis or other evidence of a psoriatic diathesis.
• Undifferentiated

Management:

Diagnosis

Arthritis is defined as the presence of a joint effusion with reduced range of motion, pain on movement and/or warmth of the joint.
Arthritis can be inflammatory or traumatic. A consistent and important clinical feature is the timing of symptoms during the day. As a general guide:

• early morning stiffness and/or stiffness after rest or sleep suggests an inflammatory cause
• postactivity pain suggests a mechanical cause.

Investigations

The diagnosis of JIA is essentially a clinical one. The laboratory investigations are only used to confirm the diagnosis and to aid the classification of JIA.

RACGP guidelines recommend

• FBC, CRP and ESR should be performed if the symptoms are present for more than four weeks.
• Rheumatoid factor (RF) should be performed in patients with polyarthritis as its presence has prognostic significance.
• ANA should be performed in all patients as it can confer the risk of asymptomatic uveitis especially in oligoarticular arthritis.
• Anticyclic citrullinated peptide (anti-CC P) antibodies
  are not routinely tested in JIA, but may indicate severe disease.
• Human leukocytic antigen (HL A) B27 should be tested in children who present with signs and symptoms consistent with enthesitis related arthritis and can indicate susceptibility to the development of axial arthritis.
• If there is concern that arthritis is part of an underlying connective tissue disease or vasculitis then dsDNA, extractable nuclear antigens (EN A), C3, C4 and immunoglobulin testing is useful.
• Imaging ( X ray +/_ USS is recommended if there is symptoms more than 4 weeks.
  

Treatment

Early referral to paediatric rheumatologist and multidisciplinary care are important.
Three mainstays of treatment.

• Non-steroidal anti-inflammatory drugs
• Disease Modifying Anti-rheumatic Drugs ( Methotrexate and biologic agents )
• Intra-articular corticosteroid injection

Course of JIA

Approximately 50% of children will have active disease
as adults.