Pseudosepsis in rheumatoid arthritis due to cellular and lipid abnormalities in synovial fluid.

In acute septic arthritis, the synovial fluid is usually frankly purulent. However, the presence of pus does not always imply the presence of infection, and some synovial fluids are easily mistaken for pus. An exaggeration of the normal leucocyte response in inflammatory joint fluids may alone simulate sepsis; marked increases in certain lipid fractions of the fluid may produce similar appearances. We describe a patient who presented with two examples of such 'pseudoseptic arthritis'.