Rheumatic diseases of the spine: imaging diagnosis.

Spinal involvement is common both in the spondyloarthritides and in rheumatoid arthritis, in which the cervical segment is selectively affected. Rheumatoid involvement of the cervical spine has characteristic radiologic manifestations, fundamentally different patterns of atlantoaxial instability. Magnetic resonance imaging (MRI) is the technique of choice for evaluating the possible repercussions of atlantoaxial instability on the spinal cord and/or nerve roots in patients with rheumatoid arthritis as well as for evaluating parameters indicative of active inflammation, such as bone edema and synovitis. Axial involvement is characteristic in the spondyloarthritides and has distinctive manifestations on plain-film X-rays, which reflect destructive and reparative phenomena. The use of MRI has changed the conception of spondyloarthritis because it is able to directly detect the inflammatory changes that form part of the disease, making it possible to establish the diagnosis early in the disease process, when plain-film X-ray findings are normal (non-radiographic axial spondyloarthritis), to assess the prognosis of the disease, and to contribute to treatment planning.