Crystal arthropathies

Crystal arthropathies are a diverse group of disorders characterized by deposition of various minerals in joints and soft tissues leading to inflammation. The patterns of presentation for different types of crystal arthritis are often characteristic enough to differentiate them from each other and from other types of inflammatory arthropathies, but mistakes can be made, leading to delayed or incorrect management. Gout is the most common of all the crystal arthropathies, and its prevalence and clinical complexity appear to be increasing. In addition to gout, which is caused by monosodium urate crystal precipitation, two other main crystal types can be associated with inflammatory symptoms because of their deposition in and around joints. These are calcium pyrophosphate dihydrate, which causes pseudogout, and basic calcium phosphate (BCP/hydroxyapatite). The most accurate way of diagnosing the common forms of crystal-associated arthritis is through the identification of specific crystal types in synovial fluid, although this is less reliable for BCP. Crystal arthritis can cause severe pain, and management generally revolves around the control of acute flares, followed by prevention of recurrent episodes, where possible. For many years the prophylaxis of gout has depended largely on the use of allopurinol, but new drugs such as febuxostat may prove to be useful for those patients who cannot tolerate allopurinol. Biologic treatments are similarly providing exciting novel treatment strategies as the pathophysiology of the disorder becomes better understood.