SERONEGATIVE SPONDYLARTHROPATHIES - IMAGING OF SPONDYLITIS, ENTHESITIS AND DACTYLITIS

Sacroiliitis is an indispensable condition for the diagnosis of ankylo sing spondylitis according to the present criteria and is usually diag nosed on standard anteroposterior radiographs of the pelvis. In cases with suspicious abnormalities (grade 1 of the New York criteria) CP pe rmits the diagnosis since it shows a higher degree of sacroiliitis. MR I is superior to CT in the early diagnosis as it can detect the cartil age abnormalities which precede bony changes. 'Romanus lesions' with ' shiny corners', 'squaring' of the vertebral bodies, syndesmophytes, sp ondylodiscitis and osteoporosis are the radiological findings of ankyl osing spondylitis. The nonmarginal, asymmetric, coarse and broad synde smophytes of psoriatic spondylitis and spondylitis associated with Rei ter's syndrome resemble the flowing bone outgrowths of diffuse idiopat hic skeletal hyperostosis (DISH). The ossification of the posterior lo ngitudinal ligament and of the flavum ligament are rare manifestations of ankylosing spondylitis. Peripheral extra-articular enthesitis is a clinical hallmark of seronegative spondylarthropathies. Plain film ra diography shows erosions and spurs but only in advanced phases. US sho ws the swelling of the entheses and the peritendinous soft tissues and the distension of adjacent bursae by fluid collection. MRI shows the inflammation of the bone adjacent to the insertion as well as the soft tissue changes. Dactylitis is another typical manifestation of serone gative spondylarthropathies. In the past it was thought to be due to c oncomitant tenosynovitis and arthritis. Recently, however, we have dem onstrated with US and MRI that the 'sausage-like' appearance is due to the flexor tenosynovitis and that joint capsule distension is not ind ispensable. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved .