Arthritis Rheumatology 2023 Jan 26 Online Kiil RM, et al.
May 2, 2023, 11:10 a.m.
Presented By
Dr Walter Maksymowych
MB ChB, FRCP(C), FACP
Chief Medical Officer, CARE Arthritis; Professor of Medicine, University of Alberta
Synopsis
Introduction
It has been known for some time that bone marrow edema (BME) may be observed in the sacroiliac joints (SIJ) on MRI in postpartum women which is not necessarily associated with low back or buttock pain.
It is thought that postpartum BME is related to birth trauma but there have been no prospective studies evaluating SIJ abnormalities on MRI during healthy pregnancy to determine when BME first becomes evident.
There is little information on the precise localization of the BME and the degree of its persistence during propsective follow up post-partum.
Systematic assessment of structural lesions in the SIJ on MRI and their evolution during and after pregnancy are very sparse.
Methods
MRI was performed on 50 consecutive healthy pregnant women attending antenatal care at gestational weeks 20 and 32 and at 3, 6, and 12 months postpartum.
MRI was also performed on an additional 53 healthy postpartum women at 3, 6, and 12 months
MRI scans in the postpartum period were assessed in both the oblique coronal and semiaxial orientations to permit precise localization of BME
BME and structural MRI lesions in the SIJ were quantified using the Spondyloarthritis Research Consortium of Canada (SPARCC) methods
MRI lesions were also assessed using the CARE ARTHRITIS web-based interface according to the 2021 ASAS definitions for definite BME (present in ≥4 SIJ quadrants), erosion (present in ≥3 SIJ quadrants), and fat lesion (present in ≥5 SIJ quadrants) (Maksymowych et al. Rheumatol 2021; 60: 4778-89).
Detailed clinical evaluation for axSpA was performed at 12 months.
Results
BME was already evident at 20 weeks (62%) and 32 weeks (73%) of pregnancy
Prevalence and extent of BME peaked at 3 months postpartum, where 68.7% and 41.0% of women had a SPARCC BME score of ≥1 or ≥4, respectively.
At 12 months postpartum, SPARCC BME scores of ≥1 and ≥4 were reported in 53.5% and 19.7% of women, respectively.
At 12 months postpartum, sacroiliitis according to the 2021 ASAS definition for definite BME was found in 21%.
BME was most frequently observed in the anteromedial cartilaginous portion of the ilium and sacrum.
Definite erosion according to the 2021 ASAS definition was rare (2.8%).
Image provided by courtesy of Dr. Ulrich Weber
Commentary
What is particularly surprising about this study is the finding that BME was already evident in the majority of women by 20 weeks of gestation although the extent was not possible to determine as only a semiaxial MRI scan was obtained to reduce scan times in the anterpartum period. The extent of BME was substantial in the postpartum period, where an additional oblique coronal scan was obtained, with 43% demonstrating definite BME per the 2021 ASAS definition at 3 months postpartum. The pattern of BME, being localized to the anteromedial regions of ilium and sacrum, is comparable to what may be observed in osteoarthritis, suggesting a mechanical stress component as the primary etiology becoming evident early in pregnancy. Erosion is a much more specific finding although this is difficult to detect reliably in view of the sclerosis and bone remodeling with irregular bone contours that may be observed in the postpartum period. Because of this, routine MRI evaluation increasingly includes the use of high resolution, thin slice, erosion-specific sequences which accentuate the contrast between cartilage and subchondral bone to permit more sensitive detection of erosion. Consequently, diagnostic evaluation of axSpA in postpartum women should rely more on detection of structural as opposed to inflammatory lesions.
What is particularly surprising about this study is the finding that BME was already evident in the majority of women by 20 weeks of gestation although the extent was not possible to determine as only a semiaxial MRI scan was obtained to reduce scan times in the anterpartum period. The extent of BME was substantial in the postpartum period, where an additional oblique coronal scan was obtained, with 43% demonstrating definite BME per the 2021 ASAS definition at 3 months postpartum. The pattern of BME, being localized to the anteromedial regions of ilium and sacrum, is comparable to what may be observed in osteoarthritis, suggesting a mechanical stress component as the primary etiology becoming evident early in pregnancy. Erosion is a much more specific finding although this is difficult to detect reliably in view of the sclerosis and bone remodeling with irregular bone contours that may be observed in the postpartum period. Because of this, routine MRI evaluation increasingly includes the use of high resolution, thin slice, erosion-specific sequences which accentuate the contrast between cartilage and subchondral bone to permit more sensitive detection of erosion. Consequently, diagnostic evaluation of axSpA in postpartum women should rely more on detection of structural as opposed to inflammatory lesions.