The crystals that accumulate in joints during gout are composed of what substance?

• A. Calcium pyrophosphate dihydrate crystals
• B. Cholesterol crystals
• C. Monosodium urate crystals
• D. Hydroxyapatite crystals

Answer: (C)

Gout involves deposition of monosodium urate crystals in joints due to elevated uric acid levels. Uric acid is the end product of purine metabolism, and when its concentration in the blood exceeds solubility, it crystallizes as monosodium urate and accumulates in synovial fluid and cartilage. These needle-shaped crystals are negatively birefringent under polarized light microscopy, which helps distinguish gout from other crystal arthropathies. The inflammatory attack is driven by the crystals activating neutrophils and the inflammasome, leading to the intense pain and swelling.

Calcium pyrophosphate dihydrate crystals cause pseudogout, and they are typically rhomboid-shaped and positively birefringent. Cholesterol crystals are not the main issue in gout. Hydroxyapatite crystals are seen in calcific tendonitis or basic calcium phosphate deposition diseases, not gout.