Which type of synovial fluid crystal is fine, needle-like negatively birefringent (gout)?

Which type of synovial fluid crystal is fine, needle-like negatively birefringent (gout)?

• A. Monosodium urate
• B. Calcium pyrophosphate
• C. Cholesterol
• D. Uric acid crystals

Answer: (A)

Monosodium urate crystals. In gout, the crystals in the joint fluid are fine, needle-shaped and show negative birefringence under polarized light, appearing yellow when aligned with the slow axis of the compensator and blue when perpendicular. This combination of needle morphology and negative birefringence distinguishes gout from other crystal arthritides, such as calcium pyrophosphate which are rhomboid and positively birefringent. The crystals form when uric acid levels are high (hyperuricemia), crystallize as monosodium urate, and provoke inflammatory arthritis.

Monosodium urate crystals. In gout, the crystals in the joint fluid are fine, needle-shaped and show negative birefringence under polarized light, appearing yellow when aligned with the slow axis of the compensator and blue when perpendicular. This combination of needle morphology and negative birefringence distinguishes gout from other crystal arthritides, such as calcium pyrophosphate which are rhomboid and positively birefringent. The crystals form when uric acid levels are high (hyperuricemia), crystallize as monosodium urate, and provoke inflammatory arthritis.