A 38-year-old woman presents with acute-onset pain and swelling of the right wrist and knee. Synovial fluid analysis reveals positively birefringent rhomboid-shaped crystals under compensated polarized light microscopy. Serum urate is normal. What is the most likely diagnosis?
- A Calcium pyrophosphate deposition disease (pseudogout) ✓
- B Gout
- C Septic arthritis
- D Rheumatoid arthritis flare
Correct answer: A. Calcium pyrophosphate deposition disease (pseudogout)
Explanation
Calcium pyrophosphate dihydrate (CPPD) crystals are positively birefringent and rhomboid in shape. Gout crystals are negatively birefringent needle-shaped. Normal serum urate during an acute flare does not exclude gout, but the crystal morphology distinguishes CPPD. Chondrocalcinosis on imaging further supports this diagnosis.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.