Paediatrics: Rheumatoid factor-negative polyarthritis

Rheumatoid factor-negative polyarthritis

30%  of JIA     cases. Previously      known as      polyarticular        onset JCA.

Characterized by 5 or more affected joints within first 6mths.

Clinical features

•   Diagnosis of exclusion: IgM RF-negative 3mths apart.

•   Systemic features: low grade fever and transient rashes possible, but mild.

•   Asymmetrical joint involvement of any joint including jaw, cervical spine, wrists and fingers, and subtalar joints.

•   Joint swelling leads to limited mobility and muscle wasting.

•   Chronic hyperaemia leads to accelerated bone growth and premature cartilage fusion. Common sites: carpus, subtalar, jaw (micrognathia, dental malocclusion); cervical spine (C3–5 apophyseal joint fusion with instability above and below).

•   Tenosynovitis and bursitis around fingers and feet.

•   Flexion contractures at elbows, knees, and hips.

Investigations

•   Blood: FBC, CRP, ANA.

•   X-ray: affected joints.

Treatments

Start treatment as soon as possible.

•   NSAIDs for 8wks in adequate dose, plus intra-articular steroids to target joints.

•   Start DMARDs early to try and induce remission with oral or SC MTX (use sulfasalazine or azathioprine if intolerant to MTX;).

•   Remission: continue NSAID for 6mths and DMARD for 1yr.

•   Persistent arthritis: intra-articular steroids into target joints + combination DMARDs.

•   Etanercept: anti-TNF therapy if intolerant or unresponsive to MTX.

Prognosis

Heterogeneous group of conditions with variable prognosis. Prognosis has dramatically improved in recent years with the aggressive use of MTX and anti-TNF therapy. However, up to a third will have persistent deformity, disability, and disease activity into adult life.