Tophaceous pseudogout of the femorotibial joint in a painted turtle (Chrysemys picta).

A 5-year-old painted turtle (Chrysemys picta) presented with a 1cm nodular enlargement of the right femorotibial joint. The right leg was amputated, because the nodule continued to grow and motor problems appeared. The cut surface of the nodule was yellowish white, and had a colloidal to chalky gross appearance. Microscopically, a multinodular foreign-body granuloma was observed around the joint capsule. Morphological and histochemical examination showed that the foreign body consisted of calcium pyrophosphate. Histological findings revealed that the articular cartilage was mainly involved in the pathological onset of the disease, and was therefore diagnosed as tophaceous pseudogout. This disease is generic in elderly people, but is rare in animals. Also, there are only three reports in reptiles.