A 74-year-old woman develops an acutely swollen, painful right knee three days after uncomplicated elective gallbladder surgery. She is afebrile. Radiographs show linear calcification of the menisci. Synovial fluid analysis reveals 12,000 leukocytes/uL with rhomboid-shaped crystals showing weak positive birefringence under polarised light. What is the most likely diagnosis?

• A Gouty arthritis caused by monosodium urate deposition
• B Late-onset rheumatoid arthritis
• C Hydroxyapatite deposition disease
• D Acute calcium pyrophosphate crystal arthritis (pseudogout) ✓

Explanation

Rhomboid crystals with weakly positive birefringence are diagnostic of calcium pyrophosphate deposition disease, which characteristically flares in elderly patients after surgery, trauma or serious illness. The radiographic finding of chondrocalcinosis supports this. Urate crystals are needle shaped and strongly negatively birefringent, which excludes option A. Hydroxyapatite produces amorphous non-birefringent material seen mainly in calcific tendinitis, and RA does not produce crystals.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.