Summary

This is a case of a 65-year-old man with seropositive erosive rheumatoid arthritis (RA), well controlled on methotrexate, sulfasalazine, low-dose prednisolone and monthly infusions of tocilizumab. He presented with a 3-week history of pain and swelling in his left knee, gradually increasing in severity with an inability to bear weight . He was systemically well with normal vital signs. Examination confirmed an effusion and aspiration was turbid in appearance. C reactive protein (CRP) was normal. He was treated empirically with antibiotics. Synovial fluid and blood cultures confirmed Staphylococcus aureus infection. He completed a 6 weeks course of antibiotics with complete resolution of symptoms. Throughout the treatment his CRP remained normal which is likely to have been the result of prior treatment with tocilizumab.