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Swollen Knee (Monoarthritis)

A 5 year old girl presents with 6 weeks of leg pain and noted to be stiff in the mornings. She is unable to sit cross-legged on the floor at school. Otherwise she is well with no systemic upset and no fever.

pGALS shows swollen knees, right more than the left. Otherwise physical examination is normal. Blood tests from her paediatrician are normal full [complete] blood count and ESR, CRP.  ANA (using Indirect Immunofluorescence) is negative. 

Diagnosis - Oligoarticular JIA.


  • Prescribed NSAIDs and analgesia.
  • Recommended for intra-articular joint injection under general anaesthetic (or in some countries, conscious sedation may be used).
  • Referred to ophthalmology for eye screening (even though she is ANA negative, she is still at risk of uveitis).
  • She attended for joint injections 2 weeks later and was noted to have large effusions of both knees. These were aspirated and injected corticosteroid (preferably triamcinolone hexacetonide 1mg/kg/joint).  
  • Bloods are repeated whilst under anaesthetic: Full [complete] blood count normal, inflammatory markers (normal), varicella serology IgG positive indicative of previous infection and immunity.
  • Physiotherapy as an outpatient.
Why was her varicella serology checked ?

This child has Oligo-articular JIA.

One third of children with this JIA subtype may develop a polyarticular course (if this happens after 6 months, then it is called Extended Oligoarticular JIA), and warrant systemic immunosuppression (with methotrexate or may progress to a biologic). If varicella negative then varicella vaccination (a live vaccine) would be recommended in case she needs to have methotrexate in the future. Varicella infection can be serious in children who are immunosuppressed. 

The photograph below shows zoster infection in a child who is immunosuppressed.