Board Review: Crystal Induced Synovitis
55 year old male presents to your emergency department with a warm, erythematous, swollen right knee. You perform an arthrocentesis of the joint and synovial fluid analysis reveals a WBC 8,000 cells/µL with 50% PMNs and positive birefringent crystals. Which of the following is the most likely diagnosis? (scroll down for the answer)
A) Gout
B) Pseudogout
C) Gonococcal Septic Arthritis
D) Non-gonococcal Septic Arthritis
The correct answer is B) Pseudogout
A synovial fluid analysis with WBC 2,000 cells/µL to 50,000 cells/µL and >50% PMNs suggests an inflammatory arthritis, while an analysis with WBC > 50,000 cells/µL and >75% PMNs suggests a septic arthritis. The crystals associated with gout are negative birefringent, while the crystals associated with pseudogout are positive birefringent.
Gout Pearls
- Most common joint involved: 1st MTP
- Crystals: needle like, monosodium urate, negative birefringent
- XR findings: “rate bite” erosions
- Treatment: NSAIDs, colchicine, steroids
Pseuodogout Pearls
- Most common joint involved: Knee
- Crystals: rhomboid shape, calcium pyrophosphate, positive birefringent
- XR findings: white lines of chondrocalcinosis
- Treatment: NSAIDs, colchicine, steroids
Stapczynski, J. Stephan,, and Judith E. Tintinalli. Tintinalli's Emergency Medicine: A Comprehensive Study Guide. 7th ed. New York, N.Y.: McGraw-Hill Education LLC., 2011.