Objective: To determine the prevalence and diagnostic value of pelvic enthesitis on MRI of the sacroiliac (SI) joints in spondyloarthritis (SpA).
Materials and methods: A retrospective study in 444 patients aged 17-45 years old with MRI of the SI joints and with clinically suspected sacroiliitis was performed. Patients were classified as having SpA if they fulfilled the Assessment of Spondyloarthritis International Society (ASAS) criteria. Pelvic enthesitis on MRI was correlated with the final diagnosis. Sensitivity, specificity, positive and negative likelihood ratio (LR) and predictive values (PV) of pelvic enthesitis for the diagnosis of SpA were calculated.
Results: MRI showed pelvic enthesitis in 24.4 % of patients with SpA and in 7.1 % of patients without SpA. Presence of any enthesitis had sensitivity, specificity, LR+, LR-, PPV and NPV of 24.4 %, 92.9 %, 3.45, 0.81, 69.4 % and 65.2 % for the diagnosis of SpA, respectively. The most commonly affected entheses were the longitudinal ligament insertion (4.5 %), the retroarticular ligaments (4.1 %) and the pubic symphysis (4.1 %). The sites of enthesitis with the highest PPV for SpA were the iliac crest/wing (85.7 %) and the retroarticular ligaments (81.3 %).
Conclusion: Nearly one fourth of SpA patients with suspected sacroiliitis showed pelvic enthesitis on MRI. Such pelvic enthesitis has a high specificity for the diagnosis of spondyloarthritis.
Key points: • Enthesitis is the primary clinical feature of spondyloarthritis. • Magnetic resonance imaging of the sacroiliac joints can demonstrate pelvic enthesitis. • Pelvic enthesitis has a high specificity for the diagnosis of spondyloarthritis.