1248: A Retrospective Chart Review Examining How a Change in MRI Protocol Could Affect the Diagnosis of Axial Spondyloarthritis

Alexa Kouroukis¹, Manisha Mulgund², Leilani Famorca³, Pauline Boulos¹ and Viktoria Pavlova⁴, ¹McMaster University, Hamilton, ON, Canada, ²Trillium Health Partners, Ancaster, ON, Canada, ³McMaster University, Milton, ON, Canada, ⁴McMaster University, Ancaster, ON, Canada

Background/Purpose: St. Joseph's Healthcare Hamilton (SJHH) recently changed their MRI-axial spondyloarthritis (axSpA) protocol, used to diagnose patients with axSpA, from an MRI of the spine and sacroiliac joints (SI) to an MRI of only the SI joints. The aim of this study is to determine if the accuracy of diagnosing axSpA will be reduced with this new limited MRI protocol, as well as to see if there are any characteristics that differentiate patients with sacroiliitis ± spondylitis compared to those with spondylitis alone.

Methods: This was a retrospective chart review. Using electronic medical records from four community rheumatologists in Southwestern Ontario, a computerized search was performed using the diagnostic code 720 to identify eligible patients. All patients newly diagnosed with axSpA or ankylosing spondylitis (AS) between January 2011 to January 2021 who had an MRI-axSpA protocol performed at SJHH were included. Their MRI reports were reviewed to determine how many of these patients had sacroiliitis ± spondylitis versus spondylitis alone. Patient characteristics were also extracted, including age, sex, duration of symptoms, measures of disease activity, and laboratory markers. Continuous variables were analyzed using a t-test and categorical variables were analyzed using Pearson's chi-squared test.

Results: 275 patients were identified, of which 86 patients fulfilled criteria and were included in the study. Baseline characteristics of this entire cohort were mean age of 42, equal numbers of men and women, mean duration of back pain of 9 years, 56% HLA-B27+, mean CRP of 9.62 mg/L, and mean BASDAI score of 5.7. Analysis showed 82 patients had sacroiliitis ± spondylitis and 4 had spondylitis alone. The change in MRI protocol would be 95% accurate in diagnosing axSpA in this cohort of patients. Unfortunately, there were no statistically significant differences in the characteristics analyzed between groups (See Table 1).

Table 1. Patient demographics stratified by MRI findings

Patients (n=86)
Sacroiliitis ± spondylitis (n=82)	Spondylitis alone (n=4)	p-value
Age (years)	42 ± 14.2	54 ± 7.6	0.075
Female – no. (%)	40 (49)	3 (75)	0.306
Mean duration of back pain (years)	8.93 ± 10.7	10.1 ± 14.0	0.902
HLAB27+ – no. (%)	45 (55)	3 (75)	0.670
CRP (mg/L)	9.71 ± 19.0	9.80 ± 10.4	0.984
BASDAI	5.70 ± 2.0	6.97 ± 0.6	0.248

Conclusion: In this population, the updated protocol would save time and money while continuing to effectively diagnose patients with axSpA 95% of the time. Clinicians should be aware that although most patients with axSpA will be identified by an MRI of the SI joints alone, a small proportion of patients could be missed. Clinically it appears that patients who are older, female, and/or HLA-B27+ may be more likely to have spondylitis alone, however there were no statistical differences in our measurements, likely related to the small sample size of this group. Next steps would be to expand this study to include a larger cohort of patients in order to make more robust conclusions.
Disclosures: A. Kouroukis, None; M. Mulgund, None; L. Famorca, None; P. Boulos, None; V. Pavlova, None.