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Abstract Number: 0900

The Phenomenon of Fused Sacroiliac Joints but Absent Syndesmophytes in Long Standing Ankylosing Spondylitis Patients: Data from a Prospectively Followed Cohort

Lauren Ridley1, Mark Hwang2, John Reveille3, Lianne Gensler4, Mariko Ishimori5, Matthew Brown6, Mohammad Rahbar7, Amirali Tahanan8, Michael Ward9, Michael Weisman10 and Thomas Learch11, 1McGovern Medical School, Katy, TX, 2McGovern Medical School at the University of Texas Health Science Center at Houston, Houston, TX, 3Division of Rheumatology, The University of Texas Health Science Center at Houston, Houston, TX, 4Department of Rheumatology, University of California San Francisco, San Francisco, CA, 5Cedars-Sinai Health System, Los Angeles, CA, 6King's College London, London, United Kingdom, 7Division of Clinical and Translational Sciences, Department of Internal Medicine, The University of Texas Health Science Center at Houston, Houston, TX, 8McGovern Medical School, Houston, TX, 9Intramural Research Program, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Maryland, United States, Rockville, MD, 10Adjunct Professor of Medicine, Stanford University; Distinguished Professor of Medicine Emeritus, David Geffen School of Medicine at UCLA, Los Angeles, CA, 11Cedars-Sinai, Los Angeles, CA

Meeting: ACR Convergence 2021

Keywords: Ankylosing spondylitis (AS), Cohort Study, gender

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Session Information

Date: Sunday, November 7, 2021

Title: Spondyloarthritis Including PsA – Diagnosis, Manifestations, & Outcomes Poster II: Imaging in Spondyloarthritis (0897–0907)

Session Type: Poster Session B

Session Time: 8:30AM-10:30AM

Background/Purpose: Ankylosing Spondylitis describes disorders of inflammation and damage to the spine and sacroiliac (SI) joints. Clinicians have observed, on occasion, AS subjects with fused SI joints but little or no spinal involvement; is there truly a subgroup with fused SI joints and long-standing disease but absent radiographically demonstrated spinal syndesmophytes? No study has assessed the subset with long standing disease with fused SI joints but no radiographic spinal disease. Using a large multi-center cohort, the purpose of this study was to identify factors associated with discordant SI joint and spinal radiographic severity in AS patients.

Methods: Patients met the modified New York criteria for AS. Study visits every 4-6 months included CRP levels, demographic and social information. Radiographs of the pelvis and lateral spine were performed every 2 years. We included 354 patients with fused SI joints and disease duration of at least 20 years. We employed classification and regression trees (CART) analysis to examine the subset of patients with fused SI joints but no syndesmophytes. We defined no-syndesmophytes as mSASSS< 2 at all cervical- and lumbar-spine levels, and the presence of syndesmophytes as mSASSS≥ 2. We also conducted logistic regression models.

Results: Of the 354 patients with long standing disease and fused SI joints, 6.5% did not have syndesmophytes. Gender was the strongest factor associated with lack of syndesmophytes on CART analysis. Females accounted for 16% of the subgroup, and of these, 20% did not have syndesmophytes. Males were 84% of the subgroup and 4% did not have syndesmophytes (Figure 1). Univariable logistic regression modeling corroborated this finding with OR 5.83 (95% CI 2.43, 14.00), p­-value was < 0.001 with females more likely to not have syndesmophytes (Table 1).

In men, age of onset was the next important predictor. 26% of males had age of symptom onset less than 18 years, and 8.6% of these did not have syndesmophytes (Figure 1). Investigating interactions between male gender and age of symptom onset, on multivariable analysis the p-value was 0.006 with OR 35.65 (95% CI 2.81, 451.60) (Table 2) with men who had age of symptom onset < 18 years being less likely to have syndesmophytes.

All 23 patients who did not have syndesmophytes were HLA-B27 positive.

Conclusion: Of our subgroup, 6.5% of patients lacked syndesmophytes. Gender was the most important variable, with women being more likely to lack syndesmophytes despite having complete SI fusion with long disease duration. Age of symptom onset may also be an important variable in male gender subjects. All of the non-syndesmophyte group were HLA-B27 positive raising the possibility that HLA-B27 positivity may be more associated with sacroiliitis than proliferative spinal bone disease. Our study is distinct in assessing this subpopulation of fused SI joints with long disease duration but no spinal disease. Further studies are needed to elucidate why AS disease behaves differently in this and other subgroups.

Figure 1: CART Analysis. Yellow values = percentages of the total subgroup population. White values = likelihood of not having syndesmophytes.

Table 1: Factor associated with syndesmophytes for patients with disease duration ≥20 years and grade IV sacroiliitis based on univariable logistic regression model (N=354 patients).

Table 2: Factors associated with syndesmophytes for patients with disease duration ≥ 20 years and grade IV sacroiliitis based on multivariable logistic regression with first-order interactions (N=354 patients).


Disclosures: L. Ridley, None; M. Hwang, Novartis, 2, UCB, 2, University of Texas Health Science Center at Houston (UTHealth) Center of Clinical and Translational Sciences KL2 program, 5; J. Reveille, UCB, 1, Eli Lilly, 1, Eli Lilly, 5, Novartis, 1; L. Gensler, Novartis, 5, UCB, 5, Eli Lilly, 2, Gilead, 2, Pfizer, 2, Pfizer, 5, Janssen, 2, UCB, 2; M. Ishimori, None; M. Brown, None; M. Rahbar, None; A. Tahanan, None; M. Ward, None; M. Weisman, Novartis, 2, Gilead, 2, GSK, 2, UCB, 2; T. Learch, None.

To cite this abstract in AMA style:

Ridley L, Hwang M, Reveille J, Gensler L, Ishimori M, Brown M, Rahbar M, Tahanan A, Ward M, Weisman M, Learch T. The Phenomenon of Fused Sacroiliac Joints but Absent Syndesmophytes in Long Standing Ankylosing Spondylitis Patients: Data from a Prospectively Followed Cohort [abstract]. Arthritis Rheumatol. 2021; 73 (suppl 9). https://acrabstracts.org/abstract/the-phenomenon-of-fused-sacroiliac-joints-but-absent-syndesmophytes-in-long-standing-ankylosing-spondylitis-patients-data-from-a-prospectively-followed-cohort/. Accessed .
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