Sacroiliitis Testing Recommended In Juvenile SpA With Positive HLA-B27

Researchers from the Children’s Hospital of Philadelphia and the Perelman School of Medicine have found sacroiliitis to be common in children with newly diagnosed spondyloarthritis (SpA), and that the sacroiliitis is frequently asymptomatic.

The researchers also found that in HLA-B27-positive children with elevated C-reactive protein (CRP) levels, the probability of having sacroiliitis was 0.84, compared with 0.33 in HLA-B27-negative children.

They therefore recommend that all children with juvenile SpA who are HLA-B27-positive, especially those with elevated CRP levels, should be considered for sacroiliitis screening.

In the first study to evaluate the prevalence of sacroiliitis by magnetic resonance imaging (MRI) at the time of diagnosis of juvenile SpA, Pamela Weiss, MD, MSCE, from Children’s Hospital of Philadelphia and colleagues studied 40 children ages 8 to 18 years with newly diagnosed juvenile SpA as well as 14 healthy controls. The researchers assessed the participants with physical examination, anteroposterior pelvic radiograph, and pelvic MRI.

The researchers found that 8 of the children (20%) with juvenile SpA had active sacroiliitis. Of these 8 children, 7 (88%) also had evidence of erosions or sclerosis.

Based on their findings, the researchers raised questions about whether the International League of Associations for Rheumatology (ILAR) Sacroiliac Joint Arthritis Definition and Axial SpA Definition should be redefined for children, recommended increased use of MRI testing for the diagnosis of sacroiliitis, and explored possible interpretations of asymptomatic bone marrow edema (BME).

Re-Examining the ILAR Sacroiliac Joint Arthritis Definition

Of the children with active sacroiliitis on imaging, 5 out of 8 (63%) did not have current or a history of back pain or tenderness with direct palpation of the sacroiliac joints. Conversely, of the 9 subjects who reported inflammatory back pain, only 2 (22%) had sacroiliitis.

“None of the physical examination features traditionally thought to be indicative of sacroiliitis (sacroiliac tenderness, FABER [flexion, abduction, and internal rotation] sign, or decreased lateral or forward flexion) had a significantly different prevalence between those with and without sacroiliitis,” the authors wrote.

This finding raises the question of whether the current definition of sacroiliac joint arthritis used in the ILAR criteria(tenderness on direct palpation) should be revisited. The researchers found that 15 of the children in the study with juvenile SpA had sacroiliac arthritis according to the ILAR sacroiliac joint arthritis definition, but not by MRI.

“The low positive predictive value and potential overdiagnosis of sacroiliitis may lead to unnecessary treatment with anti-TNF agents or other systemic agents, especially if there are no other involved joints,” the authors wrote. “This uncertainty also raises the question of whether imaging should be performed to confirm sacroiliitis if tenderness on examination is elicited, particularly if systemic inflammatory treatment will be initiated based on this examination finding.”

Re-Examining the Axial SpA Definition For Children

Of the 8 children in the study found to have active sacroiliitis on MRI examination, 5 did not have current or a history of back pain and only 2 participants (25%) had inflammatory back pain.

“Our results raise the issue that the adult definition of axial SpA, which mandates the presence of inflammatory back pain, is unlikely to perform well in juvenile SpA, given the low sensitivity of inflammatory back pain for sacroiliitis in this study,” the authors wrote. “Indeed, other studies have suggested that the most important manifestation of early disease in children is peripheral arthritis and enthesitis, not inflammatory back pain.”

Increasing MRI Testing for Sacroiliitis

Although radiographs are still the gold standard to diagnose ankylosing spondylitis, the authors found that early sacroiliitis would have been missed in approximately one-third of the children if radiographs had been the only test conducted. They note that MRI has become an accepted method for identifying sacroiliitis and advocate for its use.

“Insurance companies often will not pay for an MRI until a radiograph has been performed, although this practice may cause unnecessary

radiation exposure to the juvenile SpA population and may result in early cases of sacroiliitis going undetected if MRI is not subsequently performed,” the authors wrote.

Possible Interpretations of Asymptomatic Bone Marrow Edema

The researchers found that in the 8 children with active sacroiliitis, 7 also had evidence of structural damage, portending continued disease progression.

However, the researchers also found asymptomatic BME in 1 healthy child in the control group who did not have any other symptoms of juvenile SpA. The cause of the BME was unclear, and the researchers noted that the abnormal signal could have been secondary to any number of factors, including a small fibrous or cartilaginous lesion or BME perhaps from physical activity.

The researchers also found that the abnormal focus of signal intensity in this participant appeared different from the BME pattern in the children with juvenile SpA, but noted that “nevertheless, the finding of BME in a control subject raises the possibility that some cases of BME in children and adolescents with juvenile SpA, particularly those that are asymptomatic and without evidence of structural damage, may not represent true inflammatory sacroiliitis.”

Summary and Clinical Applicability

In the first study to evaluate the prevalence of sacroiliitis by MRI at the time of diagnosis of juvenile SpA, researchers have found sacroiliitis to be common in children with newly diagnosed SpA, and that the sacroiliitis is frequently asymptomatic.

In HLA-B27-positive children with elevated CRP levels, the probability of having sacroiliitis was 0.84, compared 0.33 in HLA-B27-negative children. The researchers therefore recommend that all children with juvenile SpA who are HLA-B27-positive, especially those with elevated CRP levels, should be considered for sacroiliitis screening.

Reference

Weiss PF, Xiao R, Biko DM, Chauvin NA. Assessment of sacroiliitis at diagnosis of juvenile spondyloarthritis by radiography, magnetic resonance imaging, and clinical examination. Arthritis Care Res. 2016;68(2):187-194. doi:10.1002/acr.22665.