Spinal ankylosing spondylitis: a variant form of ankylosing spondylitis or a distinct disease entity?

In a population survey of ankylosing spondylitis (AS) seven subjects, six males and one female, had x-ray changes in the lumbar spine typical of AS but without concomitant roentgenological sacroiliitis. The overall prevalence of such cases in the population studied was 0.37%. Four out of these seven subjects carried the tissue antigen HLA-B27 (57%). The clinical and roentgenological features of these subjects are described and it is suggested that the x-ray findings represent a mild and variant form of primary or definite AS.