Calcium apatite crystals in synovial fluid rice bodies.

BACKGROUND: Rice bodies can occur in the joints in many rheumatic conditions, but they are most common in rheumatoid arthritis. They are generally believed to occur rarely in patients with osteoarthritis, but one study reported rice bodies with apatite crystals. OBJECTIVE: To report on a series of joint fluids with rice bodies containing apatite clumps and examine their clinical pictures. METHODS: All synovial fluid analysis reports for 10 years were reviewed for rice bodies and eight patients were reported on. A series of patients with a variety of diseases with synovial fluid rice bodies found to contain calcific material is described. All were examined by compensated polarised light and alizarin red stain, and four were examined by electron microscopy. RESULTS: The eight patients all had alizarin red S chunks embedded throughout the rice body. Transmission electron microscopy disclosed the presence of a matrix of collagen, fibrin, and amorphous materials containing typical apatite crystals. Clinical diagnoses, radiographic findings, and leucocyte counts varied, but six of the eight patients had had previous repeated corticosteroid injections into the joints. CONCLUSION: Aggregates of apatites may be more common than previously recognised in rice bodies as they are not routinely sought. Whether they are a result of joint damage or depot steroid injections and whether that might contribute to further joint injury now needs to be investigated.

Changes in the proteins coating monosodium urate crystals during active and subsiding inflammation. Immunogold studies of synovial fluid from patients with gout and of fluid obtained using the rat subcutaneous air pouch model.

OBJECTIVE: In this in vivo study, we investigated changes in the proteins that coat monosodium urate (MSU) crystals in human synovial fluid samples and rat air pouch fluid samples obtained sequentially during periods of active and resolving inflammation, in order to evaluate whether in vivo findings are consistent with hypotheses on roles of protein coating based on in vitro findings. METHODS: Crystals from patients with gout were isolated from joint fluids with acute inflammation, and subsequently from the same joints at the time inflammation was resolving. Crystals were also obtained using the rat subcutaneous air pouch model. Immunogold was used to label proteins coating MSU crystals, for light microscopy (LM) and transmission electron microscopy (TEM) studies. RESULTS: Dense immunogold-silver labeling for IgG was observed under LM on crystals from fluid with acute inflammation, whereas other proteins (apolipoproteins [Apo], fibronectin, fibrinogen, albumin) were not labeled significantly. Apo B became strongly positive on crystals as the inflammation subsided, whereas other proteins were only weakly positive and IgG became absent or weakly positive. Quantitative TEM evaluation confirmed the LM observations. CONCLUSION: This study provides the first in vivo evidence supporting the notion derived from previous in vitro studies that proteins coating MSU crystals change as inflammation evolves. Protein coatings may play an important role in the self-limited nature of gouty inflammation. IgG coating MSU crystals may enhance the inflammation. As the inflammation subsides, Apo B could displace the IgG by competitively coating sites on crystals and could contribute in part to the resolution of the acute gouty arthritis.

Reproducibility of synovial fluid analyses. A study among four laboratories.

Aliquots from 30 synovial fluids were submitted to 4 laboratories for comparison of leukocyte counts and differential cell counts, and to 3 laboratories for a search for and identification of crystals. Leukocyte counts showed only fair correlation (coefficients of 0.76-0.80) with the reference laboratory. In synovial fluid from 4 patients, there was sufficient difference in leukocyte counts to cause the fluids to be erroneously classified as either "inflammatory" or "noninflammatory". In 12 of 24 fluid specimens examined, percentages of neutrophils fell outside the 95% confidence limits of the value determined by the reference laboratory. In 7 of the 11 patients with crystals reported, discrepancies were found between the reports from 1 or more laboratories. More attention to quality control of synovial fluid analyses is important.