Background/Purpose: The mNY criteria¹, which indicate sacroiliitis of at least grade 2 bilaterally or grade 3 or 4 unilaterally, are used to classify patients as Ankylosing Spondylitis (AS). However, little is known about the occurrence of syndesmophytes in the spine in the absence of radiographic sacroiliitis. Therefore we want to investigate if syndesmophytes are prevalent in patients with chronic back pain suspected of axSpA who are not fulfilling the mNY criteria and if syndesmophytes should be included in criteria to define patients as having radiographic axSpA.

Methods: Patients with back pain (≥3 months, ≤2 years, onset ≤45 years) recruited from the 5 participating centres across Europe were included in the SPondyloArthritis Caught Early (SPACE)-cohort. All patients underwent conventional radiographs of the cervical and lumbar spine and sacroiliac (SI)-joints (X-spine and X-SI, respectively). X-spine was scored on the presence or absence of ≥1 syndesmophytes, X-SI was scored according to the mNY¹. X-rays were scored independently by 3 well-calibrated readers. Lesions on x-ray were considered present if 2/3 readers agreed.

Results: All patients with both X-spine and X-SI data available (n=302) were used for comparison. There were 26 patients (8.6%) fulfilling the mNY criteria and 7 patients (2.3%) with ≥1 syndesmophytes present in the spine. None of those 7 patients showed radiographic sacroiliitis nor active lesions on MRI of the SI joints. Two patients fulfil the ASAS axSpA criteria and 5 patients had SpA features without fulfilling the ASAS axSpA criteria. In table 1 the number and location of syndesmophytes and SpA features are presented. Most patients (n=5) had 1 syndesmophyte. The two patients with >1 syndesmophytes did not fulfil the ASAS axSpA criteria.  All patients had syndesmophytes located solely in the cervical part of the spine. None of the patients had psoriasis. Only 2/302 (0.7%) patients would be considered as having signs of radiographic axSpA if syndesmophytes (in absence of radiographic sacroiliitis) would be considered a sign of radiographic involvement.

There were 2 patients (italic in table) in whom corresponding syndesmophytes on the MRI of the spine were scored by both readers.

Conclusion: In this population, syndesmophytes in patients without sacroiliitis on radiographs and MRI are infrequent and solely located in the cervical spine. Indicating that syndesmophytes are not informative in classifying patients as having radiographic axSpA in early disease.

References ¹van der Linden S A&R 984;27:361–8

ACR Meeting Abstracts - https://acrabstracts.org/abstract/prevalence-of-syndesmophytes-in-patients-with-chronic-back-pain-suspected-of-axial-spondyloarthritis-axspa-not-fulfilling-the-modified-new-york-mny-criteria/