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.