Case #2 Answers:













Answer 1
The differential diagnosis includes bacterial and some fungal infections, crystal diseases such as gout or pseudogout, hemorrhage and trauma. Lyme disease and Reiterís syndrome could present this way, but would be accompanied by other features.












Answer 2
Aspiration of the joint with analysis of synovial fluid is the only essential test. If uric acid crystals are found, further testing is only needed to assess therapy (e.g., renal function, K for NSAID use). If crystals are not found infection becomes the likely culprit. In addition to gramstain and culture of the synovial fluid, blood cultures and culture of any potential source of infection are indicated. X-ray is not likely to yield a diagnosis, but is useful as a baseline if infection is suspected.













Answer 3
Crystal analysis, gram stain and culture and WBC are the key information obtained from synovial fluid, synovial glucose (< 50% serum) is low in bacterial infection and RA. WBC and differential allow classification into diagnostic categories.

  Normal Non-Inflammatory (DJD)  Inflammatory (RA, gout) Septic
WBC 0-200 200-2000 2000-50,000 >50,000
% PMN 25 50 75 >90













Answer 4
No further work-up needed. Decide on management. NSAID or colchicine or intra-articular steroid injection.












Answer 5
In the absence of crystals, bacterial infection is the likely cause. Synovial gram stain is positive in only 50%. Synovial and blood cultures should be sent. The patient should be admitted for IV antibiotics. Staph aureus and strep species are the most likely organisms. Drainage of the joint is an essential component of treatment.

Consider surgical drainage if you cannot adequately drain by percutaneous route.













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Answer 9