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Crystal Examination of Synovial Fluid

- Discussion:
      - careful exam to identify crystals in synovial fluid can establish a dx early and avoid unnecessary hospital admissions for treatment of suspected infectious arthritis.
      - presence of crystals does not exclude infection, esp since abnormalities such as Gout may increase likelihood of septic arthritis;
              - cultures should be performed on samples of synovial fluid if there is any concern about infection, even if crystals are present.
      - Fat Droplets:
              - large fat droplets in synovial fluid suggest frx involving marrow space;
              - small lipid droplets, which occur in pancreatic-fat necrosis or fractures, can be misread by Coulter counters as leukocytes;
              - liquid lipid crystals have characteristic Maltese-cross configuration

- Gout:

     - look for brightly birefringent needles on compensated polarized microscopy;
     - monosodium urate crystals may be seen by normal light microscopy;


     - crystals are less intensely birefringent than monosodium urate crystals;
     - more rod-shaped or rhomboid (as compared to the needles seen in gout) w/ birefringence on compensated polarized light microscopy;
     - crystals may be small & difficult to see on nl light microscopy.

- Bipyramidal oxalate crystals
     - can cause acute arthritis but are much less common and are usually seen in renal dialysis patients

Does the presence of crystal arthritis rule out septic arthritis?

Gout or 'pseudogout': how to differentiate crystal-induced arthropathies

Synovial Fluid Analysis for Diagnosis of Intercritical Gout