How is acute CPP crystal arthritis diagnosed?
When a patient presents with an acute mono- or oligoarthritis, the critical and immediate diagnostic procedure is aspiration of the joint(s). The fluid obtained may appear yellow and cloudy or even opaque and chalky because of suspended crystals. Synovial fluid is sent to the laboratory for a cell count and differential, as well as a Gram stain and bacterial culture. Synovial fluid leukocytosis with a predominance of polymorphonuclear leukocytes (PMNs) is present. A specimen of synovial fluid is also promptly analyzed for crystals by polarized light microscopy. The presence of intracellular CPP crystals confirms the diagnosis of pseudogout.