Arthropathies associated with calcium-containing crystals.

Monosodium urate crystals are clearly related to acute attacks of gout and to the hard tissue destruction of chronic tophaceous gout. Fortunately, the acute attacks are readily treated with anti-inflammatory drugs, and destructive changes due to tophi may be prevented or reversed, at least in part, by the intelligent control of serum urate levels. Control of gout is one of the premier success stories of modern medicine. In contrast, the number of patients who have arthritis associated with crystals that contain calcium appears to be rising--perhaps a function of better recognition, perhaps related to the aging of the population. CPPD and BCP crystals can be associated with acute or subacute inflammation, but as in acute gout, it is easily controlled with anti-inflammatory drugs or by local injections of corticosteroids. A direct relationship of BCP and CPPD crystals to the associated destructive arthropathies has been hypothesized and is supported by clinical observations, animal studies, and in vivo experiments. Unlike gout, which is usually associated with a systemic metabolic abnormality (i.e., hyperuricemia), calcium crystals deposition seem to be a localized phenomenon, although numerous local sites in several joints are often involved in a given patient. Tissue degeneration in gout clearly follows (tophaceous) crystal deposition. Calcium crystal deposition may follow, rather than precede, destructive joint changes. Alternatively, both destructive changes and crystal deposition may derive independently from a common, still obscure, biochemical abnormality of joint tissues. P. A. Dieppe and colleagues believe that calcium crystal deposition follows either primary or secondary tissue degeneration but that the crystals exert a positive feedback effect (amplification loop) that accelerates degeneration. Each of those formulations of a pathogenetic role for crystals may be true in a given case, analogous to the etiology of primary and secondary forms of hyperuricemia and to sodium urate crystal deposition coexistent with osteoarthritis (tophus formation in Heberden's nodes). Conclusive proof of a significant role for BCP or CPPD crystals in the pathogenesis of human joint tissue damage depends on interrupting the postulated disease mechanism and showing that this prevents joint deterioration and leads to significant repair of existing damage. Our current position is somewhat analogous to that of our colleagues who had to contend with management of gouty arthritis before the advent of effective drugs for control of hyperuricemia.