Role of Tc-Methylene Diphosphonate SPECT/CT in the Detection of Sacroiliitis in Patients with Spondyloarthropathy: Comparison with Clinical Markers and MRI.

Our rationale was to evaluate the role of Tc-methylene diphosphonate (Tc-MDP) SPECT/CT for the detection of sacroiliitis in spondyloarthropathies by comparing it with clinical markers and MRI findings. We prospectively included 155 patients (83 men and 72 women; mean age, 35.80 ± 12.40 y; range, 18-60 y) diagnosed with spondyloarthropathies as per the criteria of the European Spondyloarthropathy Study Group. All patients underwent clinical evaluation (using the Bath ankylosing spondylitis disease activity index [BASDAI]), measurement of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level, planar Tc-MDP bone scintigraphy, SPECT/CT, and MRI of the pelvic region. Using MRI as the reference criterion, the diagnostic accuracy of the clinical and scintigraphic parameters was assessed. On planar bone scintigraphy and SPECT, a score of 0, 1, or 2 was assigned when tracer uptake in the sacroiliac joint was less than, equal to, or more than that in the sacrum. A score of 2 was considered positive for the diagnosis of sacroiliitis. The sensitivity, specificity, accuracy, and positive and negative predictive values of Tc-MDP SPECT/CT were 90.0%, 80.0%, 87.0%, 92.0%, and 75.0%, respectively. The accuracy of SPECT/CT (87%) was better than that of ESR (58.1%), CRP (32.9%), BASDAI scoring (77%), and planar bone scintigraphy (53%). Similar results were found for sensitivity and negative predictive value. Regarding specificity, SPECT/CT (80%) was lower than BASDAI scoring (88.6%) and equal to planar bone scintigraphy (80%). Regarding positive predictive value, SPECT/CT (92%) was a bit lower than BASDAI scoring (93.6%). κ-values for planar Tc-MDP bone scanning and SPECT/CT were 0.167 and 0.673, respectively, indicating poor agreement for planar bone scanning and good agreement for SPECT/CT. A significant ( < 0.001) correlation ( = 0.659) was observed between SPECT/CT and MRI findings. Tc-MDP SPECT/CT has diagnostic accuracy comparable to that of MRI for the evaluation of sacroiliitis in spondyloarthropathies and can thus be used as an alternative when MRI is contraindicated. SPECT/CT shows better accuracy than planar bone scintigraphy, ESR, CRP, and BASDAI scoring in the diagnosis of sacroiliitis.