Background: Radiographic confirmation of diagnosis is important in all
diagnostic and classification criteria for spondyloarthropathy. The aim was to
evaluate computed tomography (CT) and to compare it to radiography.
Methods: A pilot study compared radiography and CT in 40 patients with
spondyloarthropathy. A study on 1425 patients examined with CT, 910 of which
also with radiography, was reported in four papers. All CT examinations were
reviewed and scored by two observers. The original outcomes from the radiography
and CT examinations were obtained from the radiology reports.
Results: CT had a higher sensitivity for sacroiliitis than radiography,
especially in early sacroiliitis. Radiography had a high rate of false negative and
false positive outcomes.
The observer agreement between two observers in a large material was good,
while the observer agreements between each of the observers and the original
radiology reports were moderate. Intraobserver agreement for a smaller part of the
material for one of the observers was moderate.
There was a change in diagnosis in three of 126 patients (2.4%) examined
more than once from normal or equivocal to unilateral or bilateral sacroiliitis. Ten
normal cases had changed to equivocal (7.9%). In further six patients (4.8%) the
diagnosis advanced from unilateral to bilateral sacroiliitis. Four equivocal cases
were classified as normal on the second study, and one case of unilateral sacroiliitis
was classified as equivocal on the second study.
Mainly multiple or large erosions seem to be a valid solitary diagnostic sign.
Small solitary or few erosions need supplemental evidence from other inflammatory
signs such as sclerosis. Inflammatory sclerosis can frequently be distinguished from
degenerative sclerosis, and can sometimes support an early diagnosis, when
erosions are not apparent. A practical CT classification for sacroiliitis consisting of
no disease, suspect disease, and disease is proposed.
Conclusions: The clinical utility of conventional radiography for evaluation
of sacroiliitis is low with a high rate of insufficient and false reports, making
radiography unsuitable for clinical use or use in population studies. CT is a robust
imaging method for suspected sacroiliitis with good observer agreement, with
higher rate of detection of sacroiliitis than radiography; also for early changes.
There is no use for repeat CT examinations for suspected sacroiliitis. The New York
criteria are unsuitable for use with CT and a new grading system for CT of
sacroiliitis is proposed
