Pseudogout refers to a disease caused by the deposition of calcium pyrophosphate crystals in the cartilage of the joints. This was discovered in 1961 when the joint fluid of gout was studied. It is called pseudogout because of the similarity to the clinical manifestations of gout. It may also be called pyrophosphate arthropathy or chondrocalcinosis, which is synovitis induced by calcium dihydrogen pyrophosphate crystals. In China, the incidence is similar in men and women, and most patients with the disease are over 30 years of age, with typical cases developing over 50 years of age. Acute attacks of pseudogout also start suddenly, with red, swollen, hot and painful joints, and fluid often accumulates in the joint cavity. It occurs most often in the knee and other common large joints such as the hip, ankle, shoulder, elbow, and epicondylar joints, and occasionally in the finger and toe joints, but rarely in the thumb as in gout. The attack is often acute in a single joint and can be triggered by surgery or trauma. In acute attacks, the examination may reveal increased blood sedimentation, increased leukocytes in the blood, calcium pyrophosphate crystals in the synovial fluid, and punctate and linear calcified spots in the articular cartilage on x-ray. Chronic pseudogout can affect multiple joints, often symmetrically, and progresses slowly, similar to osteoarthritis.