Diffuse Idiopathic Skeletal Hyperostosis—On the Wrong Side?

Purpose: Assess the additive value of repeated MRI of the sacroiliac joints (MRI–SIJ), as part of the diagnostic approach in suspected axial spondyloarthritis (axSpA) when the first MRI- SIJ was inconclusive.

Methods: Patients that underwent at least two MRI-SIJ examinations for suspected axSpA between the years 2008-2021 and whose initial MRI diagnosis was inconclusive for sacroiliitis were retrospectively evaluated for the presence of structural and active sacroiliitis lesions. Excluded were patients younger than 18 years, patients whose follow-up MRI did not adhere to an SIJ protocol, exams with less than 6 months’ interval. Index and follow-up MRI was evaluated at least two months apart. All MRI examinations were scored using a validated scoring system (Berlin score) for the presence of active and structural lesions. A global impression (presence/absence/inconclusive-sacroiliitis) was given for each examination based on the presence of structural and active lesions and their distribution pattern. Diagnoses in the index and follow-up examinations were compared.

Results: A total of 71 patients (mean age at first exam=41.0, range 14-76 years, 77.4% female) were included in the evaluation. The mean interval between index and follow-up MRI examination was 30.4 ± 25.24 months (range 6-113 months).

In 8 patients (11.2%), all females, diagnosis was changed from inconclusive to conclusive between the index to the follow-up examinations; inconclusive to definite sacroiliitis-2 patients (2.81%), inconclusive to osteitis condensans illi -5 patients (7.04%), inconclusive to normal – 1 patient (1/4%). Unchanged inconclusive diagnosis was registered in the remaining 63 patients (88.7%).

Conclusions: The additive value of repeated MRI of the sacroiliac joints in subjects with inconclusive index examination is quite limited with a low percentage of patients in which a conclusive MRI diagnosis was reached on the follow up examination.