Review Question - QID 105973

This patient's history and radiograph showing calcification of cartilaginous structures are suggestive of pseudogout. Pseudogout will present with a synovial fluid analysis with calcium pyrophosphate dihydrate (CPPD) crystals that are rhomboid in shape and have positive birefringence.

Pseudogout is diagnosed by synovial fluid analysis. It cannot be diagnosed and differentiated from gout or septic arthritis by history and physical examination alone. Pseudogout typically presents with acute onset joint tenderness, warmth, and erythema of a joint (commonly knee and wrist). Synovial fluid analysis will reveal rhomboid shaped crystals that are positively birefringent. Radiographs will often show calcification of adjacent cartilagenous structures known as chondrocalcinosis; calcium pyrophosphate dihydrate (CPPD) crystal deposits in joints. Pseudogout is typically treated with NSAIDs and intraarticular steroid injections for acute episodes.

Siva et al. discuss diagnosing acute monoarticular arthritis in adults. As with most medical conditions, it is extremely important to initially obtain a thorough history and physical exam in order to rule out soft tissue damage. The most common causes of monoarthritis in adults are gout, pseudogout, trauma, and infection. A synovial fluid analysis is often necessary to make a definitive diagnosis.

Rho et al. report a case-control study looking at the risk factors for pseudogout in the general population. They found that the risk of pseudogout was associated with hyperparathyroidism, osteoarthritis, and use of loop diuretics. Interestingly, rheumatoid arthritis, thiazide diuretic use, and BMI (all risk factors for gout) were not associated with the risk of pseudogout. The authors also make note that the avoidance of loop diuretics may in fact be beneficial in individuals that experience recurrent pseudogout.

Figure A depicts calcification of cartilagenous structures. This is called chondrocalcinosis and is evidenced in pseudogout. Illustration A depicts chondrocalcinosis of the knee with arrows specifically pointing to the area of cartilagenous calcification. Illustration B is a synovial fluid sample showing the characteristic negative birefringent needle-shaped crystals evidenced in gout. Illustration C is an image that demonstrates the characteristic positively birefringent rhomboid crystals of pseudogout.

Incorrect Answers:
Answer 1: Negative birefringence and needle-shaped crystals are suggestive of gout. These crystals are made of monosodium urate. Although a thorough history and physical are unable to differentiate between gout and pseudogout, the radiographic findings of chondrocalcinosis are more indicative of the pathologic process of pseudogout.
Answer 3: Synovial fluid more than 50,000 WBCs and a positive gram stain is suggestive of septic arthritis.
Answer 4: Crystals composed of calcium oxalate are found in renal calculi and are not isolated from synovial fluid.
Answer 5: Clear synovial fluid with less than 200 WBCs and a negative culture is considered a normal synovial fluid analysis.