Four cases of ankylosing spondylitis in medieval skeletal series from Croatia.

Osteological changes consistent with ankylosing spondylitis were observed in three males and one female skeleton recovered from four medieval sites-Velim, Koprivno, Buje, and Rijeka-all situated on Croatia's eastern Adriatic coast and its immediate hinterland. The skeletons present changes in the spine, ribs, sacrum, and innominates that are typical of ankylosing spondylitis that is a progressive, inflammatory disease of connective tissue calcification. The disease most commonly affects the sacroiliac joints, the joints of the spine, and the costovertebral joints. In the final stages of the disease, the vertebral bodies remodel and together with the associated syndesmophytes form a continuous, smooth bone surface that is sometimes referred to as "bamboo spine." The prevalence of this disorder in the analyzed Croatian samples is 4/303 or 1.3% and thus corresponds with frequencies recorded in modern European populations. Differential diagnosis rules out the possibility of DISH, rheumatoid arthritis, and melorheostosis. These are the first cases of ankylosing spondylitis identified in Croatian archaeological series.