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- Precipitation of crystals in the synovium or synovial fluid causing acute or chronic symptoms in the articular space or adjoining tissues
- Most common is monosodium urate (MU) crystals (gout); others include calcium pyrophosphate dihydrate (CPPD—pseudogout), calcium hydroxyapatite, and calcium oxalate crystals; lipid, plain calcium phosphate, and immunoglobulin crystals also described
- Intra-articular crystals initiate an immune response and neutrophil phagocytosis which release inflammatory factors as the hallmark of crystalline arthropathies.
- Joint aspiration is required for diagnosis in all but the most classic presentations of gout.
- Uncontrolled disease can lead to chronic joint changes and disability and can herald underlying comorbid disease processes.
- Most treatments are aimed at decreasing crystal-based inflammation.
- Gout arthropathy 2 to 3/1,000 person years, blacks > white, men > women (1)
- CPPD (pseudogout), hydroxyapatite, and calcium oxalate are less likely and generally confined to older patients.
- Gout: increasing over time, from 2.7% to 3.7% (NHANES III)
- Prevalence of other crystal arthropathy is not well defined.
- Calcium oxalate is rare.
Etiology and Pathophysiology
- High levels of crystal-forming molecules precipitate in synovium and synovial fluid.
- An inflammatory response is induced, attracting neutrophils to the synovial tissues.
- Subsequent phagocytosis of the crystals releases a cascade of additional inflammatory factors from neutrophils and monocytes.
- Gout: Hyperuricemia is a prerequisite of MU crystals.
- CPPD: believed to be from overproduction of pyrophosphate from chondrocytes
- Hydroxyapatite is a normal part of bone metabolism, and crystallization is seen in associated tissue damage associated with elderly joints.
- Calcium oxalate crystals form in patients with hyperoxalemia or with end-stage renal disease.
- Genetics play a role in hyperuricemia and familial CPPD disease.
- Clinical application of genetic studies limited
- Chronic renal disease
- Underlying arthritic disease
- Parathyroid disease
- Calcium, phosphorus, or magnesium derangements
Commonly Associated Conditions
- CPPD (also called chondrocalcinosis)
- Mostly idiopathic
- Hereditary CPPD
- Tissue damage
- Parathyroid, calcium, or phosphorus disorders
- Calcium oxalate
- Excessive ascorbic acid intake
- Renal failure