A “strikingly high number” of women have bone marrow edema on MRI of the sacroiliac joints postpartum, according to a prospective study of 35 patients published in Annals of the Rheumatic Diseases. Postpartum sacroiliac bone marrow edema decreases over time. Its occurrence may be associated with a shorter duration of labor and a lack of epidural anesthesia, the researchers wrote.

Sacroiliac bone marrow edema in postpartum women “persists mainly in subjects older than 30 years,” noted Thomas Renson, MD, of Ghent (Belgium) University Hospital and colleagues. “When suspecting AxSpA [axial spondyloarthritis], our data indicate the need to wait at least 6 months to perform an MRI [of the sacroiliac joints] in postpartum women and, if positive, repeat the MRI after 12 months.”

Sacroiliac bone marrow edema is a hallmark of axSpA. However, recent studies of young, active people without the disease have found a high prevalence of bone marrow edema meeting the Assessment of SpondyloArthritis International Society (ASAS) definition of a positive MRI for sacroiliitis. Researchers have reported sacroiliac bone marrow edema in women during pregnancy and after childbirth, but prior studies have not assessed the trajectory of sacroiliac bone marrow edema after delivery, Dr. Renson and his colleagues said.

To study this question, the researchers recruited 35 subjects from the department of obstetrics at Ghent University Hospital. All participants were aged 18-45 years and had an uncomplicated, vaginal childbirth. The investigators excluded patients with a diagnosis of spondyloarthritis, inflammatory bowel disease, severe scoliosis, treatment with anti–tumor necrosis factor-alpha agents, any contraindication for MRI, childbirth through cesarean section, or pregnancy with more than one fetus.

Researchers performed a baseline MRI within 10 days of when patients gave birth and another MRI after 6 months. If the second MRI fulfilled the ASAS definition of a positive MRI for sacroiliitis, another MRI was performed at 12 months. Bone marrow edema was scored using the Spondyloarthritis Research Consortium of Canada (SPARCC) method.

In all, 77% of the patients had sacroiliac bone marrow edema on MRI an average of 5 days postpartum, and 60% fulfilled the ASAS definition of a positive MRI. After 6 months, 46% had bone marrow edema on MRI, and 15% had a positive MRI according to the ASAS definition. After 12 months, MRI was positive in 12% of the subjects. There was a high prevalence of bone marrow edema “even in subjects without back pain,” the researchers said.

“Four subjects would have fulfilled the ASAS classification criteria if there was a suspicion of axSpA: Three fulfilled the ASAS definition of a positive MRI for sacroiliitis and had inflammatory back pain, [and] one had chronic back pain, a positive MRI, and skin psoriasis,” the researchers wrote.

Misdiagnosis of axSpA based on MRI findings entails risks, the authors noted. NSAIDs may be less effective in patients who do not have axSpA, and patients may be “subsequently more likely to receive ineffective biological therapy, which has significant potential side effects and encompasses high socioeconomic costs,” the investigators said.

The study was supported by an ASAS research grant. The authors declared having no competing interests.

SOURCE: Renson T et al. Ann Rheum Dis. 2020 Apr 16. doi: 10.1136/annrheumdis-2020-217095.