Rheumatoid-like arthritis in a lion tailed macaque

: Very few satisfactory models of rheumatoid arthritis (RA) exist in nonhuman species. It is particularly striking that nonhuman primates have only rarely been described to have disease processes resembling classic RA seen in humans. We describe the case of a lion tailed macaque (Macaca silenus), housed at the National Zoological Park in Washington DC, that had a polyarticular inflammatory arthropathy resembling RA. Gross and histopathologic examination of necropsy tissues and radiographic findings strongly suggest a rheumatoid-like disease, never before described in this species.