Bone marrow edema on magnetic resonance imaging (MRI) of the sacroiliac joints is associated with development of fatty lesions on MRI over a 1-year interval in patients with early inflammatory low back pain: a 2-year followup study.

Objective: To assess whether bone marrow edema (BME) detected on magnetic resonance imaging (MRI) of the sacroiliac joints (MRI-SIJ) is associated with development of structural changes on both MRI and pelvic radiographs in patients with early inflammatory back pain (IBP).

Methods: Patients with IBP ≤ 2 years were followed for 2 years with annual MRI-SIJ. MRI were scored for BME and structural changes (erosions and fatty lesions). Pelvic radiographs were graded according to the modified New York (mNY) criteria. With generalized estimated equation analysis, a time trend in the structural change scores was investigated.

Results: Sixty-eight patients [38% male; mean (SD) age 34.9 (10.3) yrs] were included. During the 2-year followup, pelvic radiograph grading remained constant. On MRI, the number of erosions per patient increased significantly (mean score 2.5 at baseline and 3.5 at 2-yr followup; p = 0.05). A trend was found for an increase in the number of fatty lesions per patient (mean score 5.4 at baseline and 8.5 at 2-yr followup; p = 0.06). Overall, BME was associated with the development of fatty lesions (right SIJ: OR 3.13, 95% CI 1.06-9.20; left SIJ: OR 22.13, 95% CI 1.27-384.50), preferentially in quadrants showing resolution of BME. In contrast, BME (or the resolution thereof) was not associated with the development of erosions.

Conclusion: BME at baseline, especially when it disappears over time, results in the development of fatty lesions, but an association with erosions could not be demonstrated.