Question

A 45-year-old male presents with discomfort in his joints. Synovial fluid aspiration reveals rhomboid-shaped positively birefringent crystals under polarized light microscopy. What is the most likely diagnosis?

• A. Gout
• B. Rheumatoid arthritis
• C. Osteoarthritis
• D. Pseudogout

Hint:

Pseudogout = rhomboid, positively birefringent crystals. Gout = needle-shaped, negatively birefringent crystals.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question provides a definitive histological description of synovial fluid crystals to differentiate between various types of crystalline arthropathies.
Step 2: Detailed Explanation:

Pseudogout (CPPD): This condition is caused by the deposition of Calcium Pyrophosphate Dihydrate (CPPD) crystals.

Crystal Morphology: CPPD crystals are characteristically rhomboid-shaped and show weak positive birefringence under polarized light (appearing blue when aligned parallel to the compensator axis).

Gout Comparison: Gout is caused by Monosodium Urate crystals. These are needle-shaped and show strong negative birefringence (appearing yellow when parallel).

Clinical Features: Pseudogout most commonly affects large joints like the knee or wrist. Radiologically, it shows "chondrocalcinosis" (calcification of articular cartilage).

Demographics: It is typically seen in older adults or associated with hyperparathyroidism, hemochromatosis, and hypomagnesemia.

Inflammatory Markers: While RA shows a high WBC count in synovial fluid, it does not present with specific crystals like gout or pseudogout.

Step 3: Final Answer:
Rhomboid-shaped, positively birefringent crystals in joint fluid are the definitive diagnostic finding for Pseudogout.