Low back pain, sacroiliitis, and the relationship with HLA-B27 in Crohn's disease

To determine the prevalence of sacroiliitis in patients who have back pain in Crohn's disease (CD) using computed tomography (CT); and to reassess the association of sacroiliitis in CD with HLA-B27.

A total of 134 consecutive patients with CD completed a questionnaire about musculoskeletal symptoms. Those reporting low back pain were assessed, including plain radiographs and CT of the sacroiliac joints. HLA-B27 status was determined in patients with and without back pain.

There were 70 (52%) patients with low back pain, of whom 31 (45%) had CT evidence of sacroiliitis. These were characterized by more frequent morning spinal stiffness and positive sacroiliac compression tests even when sacroiliitis was not suspected. Nine had previously recognized radiological and clinical ankylosing spondylitis (AS), and of these 78% were HLA-B27 positive. Of those with newly identified sacroiliitis, 14% were HLA-B27 positive. This frequency was not statistically dissimilar to the 9% HLA-B27 positivity of those without back pain.

Sacroiliitis defined by CT is a common cause of low back pain in CD. A relationship of sacroiliitis and HLA-B27 could be confirmed only for those with classical AS. Our results accord with the possibility that sacroiliitis in CD is an isolated phenomenon, which is unrelated to HLA-B27 and which may evolve into classical spinal ankylosis in genetically susceptible subjects.