Spondyloarthropathy as an Old World phenomenon.

The presence of spine and sacroiliac involvement and the nature and distribution of erosive lesions allowed definitive diagnosis of spondyloarthropathy in the great apes (Gorilla and Pan [chimpanzee]), the lesser ape (Hylobates), and Old World monkeys (Theropithecus, Papio, Cercopithecus, Macaca, Colobus, Presbytis, and Erythrocebus). Analysis of lesional character, distribution, radiological appearance, and sex ratios showed a picture indistinguishable from human spondyloarthropathy. This contrasts with orangutans (Pongo), who lack reactive bone or sacroiliac involvement. A different pathophysiology, as yet undefined, is implied for their erosive arthritis. Limited individual susceptibility to spondyloarthropathy in humans (1% to 4%), Old World monkeys (2.4%), and lesser apes (2.4%) contrasts with the high frequency of disease in the great apes (20% to 28%). The wide geographic distribution of this phenomenon suggests an African and perhaps Asian "panendemic." This natural disease state provides a unique model for in-depth analysis of the contribution of genetic and environmental factors to disease pathophysiology.