Crystal induced arthropathies
1. Big picture
Crystal-induced arthropathies are inflammatory joint diseases caused by deposition of crystals in or around joints. The two exam-critical diseases are:
- Gout = monosodium urate (MSU) crystals
- CPPD disease / pseudogout = calcium pyrophosphate crystals
Clinical pattern:
Sudden hot swollen joint → always aspirate if possible → exclude septic arthritis → look for crystals.
The most important exam trap is that hyperuricemia does not diagnose gout. The definitive diagnosis is crystal identification in synovial fluid. The attached rheumatology question file also tests this directly: monosodium urate crystals are the absolute diagnostic criterion for gout, while hyperuricemia alone is not enough.
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