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Pathology · single question

Joint aspiration in a patient with gout would show which finding?

  1. Calcium pyrophosphate crystals (positively birefringent, rhomboid)
  2. Monosodium urate crystals (negatively birefringent, needle-shaped)
  3. Elevated creatinine in synovial fluid
  4. Rheumatoid factor in synovial fluid
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Correct answer: B. Monosodium urate crystals (negatively birefringent, needle-shaped)

Gout is caused by monosodium urate crystal deposition from hyperuricemia. Synovial fluid aspiration in gout shows needle-shaped, negatively birefringent monosodium urate crystals under polarized light — this is the GOLD STANDARD diagnosis for gout. Pseudogout shows calcium pyrophosphate dihydrate (CPPD) crystals — positively birefringent and rhomboid.
  • A. ❌ Calcium pyrophosphate crystals = PSEUDOGOUT (CPPD disease) — not gout.
  • B. ✅ Monosodium urate crystals — needle-shaped, negatively birefringent; pathognomonic for gout in synovial fluid.
  • C. ❌ Creatinine is a kidney function marker found in blood, not diagnostically in synovial fluid.
  • D. ❌ Rheumatoid factor is a serum marker for RA — not found in gout synovial fluid.

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