Pos0401 Findings on Mri of the Sacroiliac Joints 7 Years After Pregnancy in Women With and Without Postpartum Buttock/Pelvic Pain

Background: Findings on magnetic resonance imaging (MRI) of the sacroiliac joints (SIJs) have a central role in diagnosing axial spondyloarthritis (SpA). However, other conditions can resemble SpA thereby challenging the interpretation of MRIs in relation to SpA. Previous studies 1-3 have shown that especially women who have recently given birth can have SpA-like changes on MRI of the SIJs, and in particular bone marrow edema (BME) is frequent in postpartum women 1, 4, however, we do not know how these changes evolve several years after childbirth. Objectives: To investigate findings on MRI of the SIJs approximately 8 years after MRI of the SIJs were performed in women with and without postpartum buttock/pelvic pain, who participated in the MASH study 1. Methods: This study is a follow-up of the two groups of postpartum women included in the MASH study: one group had postpartum buttock/pelvic pain (BPP), that either started during pregnancy or during/after childbirth and still was present 4-16 months thereafter (hereafter termed the BPP-group); the second group comprised women without postpartum buttock/pelvic pain 4-16 months after childbirth (hereafter termed the no-BPP-group). The follow-up included clinical examination, questionnaires (regarding childbirths, physical activity, symptoms including buttock/pelvic pain and diagnoses, (e.g. SpA, fibromyalgia etc.) and MRI of the SIJs and spine. MRIs were assessed using the SPARCC MRI SIJ Inflammation Index and the SPARCC MRI SIJ Structural Scores (SSS) applied on all slices of the cartilaginous parts of the joints 5, 6. In addition to SPARCC scoring, sclerosis (>0.5 cm in depth) and fat >1cm in depth were scored for each slice for each quadrant (similar to the above SPARCC principles). Images were evaluated blinded for clinical information by an experienced MRI reader (SJP) who also made an overall assessment of whether the lesions were typical inflammatory and/or structural lesions as seen in SpA, and MRI differential diagnoses of the SIJs and spine were registered. Results: Thirty-seven of the 60 women agreed to participate in the follow-up, and of these 25 (67.6%) and 12 (32.4%) belonged to the original group with and without post-partum buttock/pelvic pain, respectively. Years since the first MRI was 8, 6-10 (mean, range). The mean age was 41 years (range 32-50). The mean number of childbirths was 2.0 in the BPP-group and 2.7 in the no-BPP-group (p=0.001); mean number of years since last childbirth was 6.9 (range 4-10) in the BPP-group and 6.8 years (range 3-10) in the no-BPP-group (range 3-10). Buttock/pelvic pain at follow-up were present in 23 (92.0%) of the BPP-group and in 2 (16.7%) of the no-BPP-group (p Conclusion: Women with post-partum buttock/pelvic pain rarely develop classical MRI features of axial SpA (i.e. erosion, fat > 1 cm in depth, backfill and ankylosis) or are diagnosed as axial SpA within an 8-year follow-up. The women with post-partum pain had more sclerosis than women without buttock/pelvic pain, even up to 7 years after the last childbirth. REFERENCES: 1 Seven S, et al. Arthritis Rheumatol. 2019;71:2034-46. 2 Renson T, et al. Ann Rheum Dis. 2020;79:929-34. 3 Kiil RM, et al. Acta Radiol. 2022;63:775-84. 4 Hoballah A, et al. Ann Rheum Dis. 2020;79:1063-9. 5 Maksymowych WP, et al. Arthritis Rheum. 2005;53:703-9. 6 Maksymowych WP, et al. J Rheumatol. 2015;42:79-86. Acknowledgements: NIL. Disclosure of Interests: None declared.