Crystals and arthritis.

Abstract

Monosodium urate, calcium pyrophosphate dihydrate, and basic calcium phosphate (carbonate-substituted hydroxyapatite and octacalcium phosphate) crystal aggregates are associated with gout, pseudogout, and cartilage degeneration (osteoarthritis, Milwaukee Shoulder/Knee Syndrome), respectively. Hyperuricemia is a frequent but nonspecific and inconstant feature of gout just as an elevated synovial fluid inorganic pyrophosphate level is an inconstant feature of pseudogout. Monosodium urate, calcium pyrophosphate dihydrate, or basic calcium phosphate crystals can cause acute inflammation associated with phagocytosis by neutrophilic leukocytes. Each induces neutral protease synthesis and secretion and arachidonic acid metabolism by synoviocytes and macrophages in a dose-dependent fashion, postulated to produce the damage to bone, cartilage, and other joint tissues that is perceived clinically as tophaceous destruction or degenerative joint disease. Crystals containing calcium are potent mitogens. All three types of crystals are more common in older persons and will attract additional attention as the mean age of our population increases. Gout is perhaps the most treatable disease in medicine, although mistakes in diagnosis and in choice of appropriate therapy are very common. Acute pseudogout and acute calcific periarthritis are readily treated medically, but the chronic effects of crystals containing calcium are not. New approaches using drugs derived from scientific study of the biologic effects of these crystals may become useful therapeutically.