Two faces of "rheumatoid arthritis": type a versus type B disease.

Is rheumatoid arthritis one disease or a "catch-all" term for inflammatory arthritis that tends to spare axial joints? We have subdivided "rheumatoid arthritis," utilizing the criteria of periarticular osteopenia and marginally (distributed), symmetrical polyarticular erosions, in absence of axial (odontoid disease excepted) involvement as type A and presence of peripheral joint fusion and subchondral erosions as type B.Biomechanical analysis of axial joint sparing inflammatory arthritis also revealed the two distinct patterns. The low vibration/power cluster (type A) had symmetrical polyarticular marginal erosions, but no peripheral joint fusion. The high vibration/power cluster (type B) had both subchondral and marginal erosions, and/or peripheral joint fusion, indistinguishable from spondyloarthropathy (S).Erosive arthritis also was noted in two distinct patterns in pre-Columbian North American cemeteries. The type B pattern was never observed in populations with the type A pattern. The type B pattern was only observed in populations with spondyloarthropathy. Demographic analysis in a modern skeletal population revealed that spondyloarthropathy and type B were quite similar to each other, but easily distinguished from type A. Evaluation of over 500 skeletons of animals with erosive arthritis revealed only type B.As type B is indistinguishable from spondyloarthropathy, it is suggested that type B be recategorized with spondyloarthropathv and that only type A be classified as rheumatoid arthritis.