Pathogenesis of chondrocalcinosis and pseudogout. Metabolism of inorganic pyrophosphate and production of calcium pyrophosphate dihydrate crystals.

Calcium pyrophosphate dihydrate (CPPD) is one of several types of crystal that may be deposited in the body. The term chondrocalcinosis is used to describe the radiographic appearance of calcified deposits, notably in the articular cartilage and menisci of the knees but also in other joints.' Not all calcified deposits within joints are due to calcium pyrophosphate; however, occasional deposition of apatite,2 calcium dihydrogen phosphate,' and oxalate also occurs. McCarty was the first to identify CPPD crystals in synovial fluids taken from patients thought to have gouty arthritis,"5 He found the crystals to be the calcium pyrophosphate dihydrate salt in its triclinic form. Shedding crystals into the synovial space produces acute or chronic attacks of pseudogout.6 Certain considerations apply to all forms of crystal deposition, in particular the factors determining whether or not crystallisation occurs. This largely concerns the activity products of the ions involved, although the presence of nucleating agents or inhibitory agents, or both, must be considered. Solubilisation processes may also be important. The purpose of this presentation is twofold: (a) to review current knowledge of the metabolism of inorganic pyrophrosphate and (b) to describe some of the mechanisms that may be involved in the production of CPDD crystals, both in vitro and in