A patient with a history of gout is taking allopurinol. If gout involves the temporomandibular joint, which of the following would you expect to find in the affected joint tissue?

Correct answer: B. Monosodium urate (uric acid) crystals

• A. Cholesterol crystals are found in chronic effusions (e.g., some knee bursitis) but are not the crystal of gout.
• B. CORRECT — Gout is caused by deposition of MONOSODIUM URATE (uric acid) CRYSTALS in joints, tendons, and periarticular tissue. When gout affects the TMJ (rare but documented), synovial fluid analysis shows needle-shaped, negatively birefringent monosodium urate crystals. Allopurinol reduces uric acid production via inhibition of xanthine oxidase.
• C. Calcium pyrophosphate (CPPD) crystals are found in PSEUDOGOUT (chondrocalcinosis) — a different disease with rhomboid, weakly positively birefringent crystals.
• D. Hydroxyapatite deposits are seen in calcific tendinitis or Milwaukee shoulder — not gout.