Calcium pyrophosphate dihydrate crystal deposition in joint diseases is a we!! recognized common arthropathy associated with acute arthritis (pseudogout) as well as chronic joint disease (1). The etiology of this disorder is obscure, and an adequate animal model has yet to be found. We describe an elderly Barbary ape (Macaca sylvanus) that had calcium pyrophosphate dihydrate crystals deposited in a tissue distribution similar to that observed in humans. Crystal deposits were seen in intervertebral discs, menisci, articular cartilage, and ligament insertions. These were associated in some sites with degenerative changes of cartilage and bone. Concomitantly, the ape had skeletal hyperostosis affecting the vertebral bodies and bony excrescences at the site of ligament and tendon attachment to bone.Case report. A 20-year-old female Barbary ape (Macaca sylvanus) on exhibit at the Metropolitan Toronto Zoo but originally from the National Zoo in Washington, DC was examined because of increasing lameness. Radiographic examination showed diffuse ligamentous calcification along the anterolateral aspect of the vertebra! bodies which was most marked in the lumbar region. Localized osteophytosis of cervical, thoracic, and lumbar vertebra! bodies was also seen. Hip, knee, and elbow joints showed degenerative changes characterized by narrowing of the joint space, subchondral sclerosis, and marginal osteophyte formation. There was calcification of tendon insertions at the ankle and elbow. Because of increasing disability and repeated attacks by others in her group, she was killed. Postmortem examination was performed at the Metropolitan Toronto Zoo, and the carcass was forwarded to Mount Sinai Hospital for further investigation of the skeletal lesions.Antemortem blood analysis was within normal limits, except for alkaline phosphatase which was markedly elevated at 217 IU (normal 0-95 IU). The serum calcium was 9.9 mg/dl (normal 8.8-103, phosphorus was 3.9 mgldl (normal 2.74.2), and albumin was 3.4 gmldl.Materials and methods. The skeletal tissues were examined and fixed in acetate buffered formalin. The lumbar spine and knee joints were cut sagitally at 1.0-cm intervals and x-rayed in a Faxitron, Mode! 8050-010, self-contained x-ray unit. Representative sections of the soft tissue and cartilage were removed, and the bone specimens then were decalcified in RDO, solution and double-embedded in celloidin-paraffin. Five-micron thick unstained sections and sections stained with hematoxylin and eosin and toluidine blue were prepared for light microscopic examination. A

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