Open Access Original research

High bone turnover assessed by 18F-fluoride PET/CT in the spine and sacroiliac joints of patients with ankylosing spondylitis: comparison with inflammatory lesions detected by whole body MRI

Dorothee R Fischer1*, Christian W A Pfirrmann2, Veronika Zubler2, Katrin D M Stumpe1, Burkhardt Seifert3, Klaus Strobel1, Giorgio Tamborrini4, Gustav K von Schulthess1, Beat A Michel4 and Adrian Ciurea4

Author Affiliations

1 Department of Nuclear Medicine, University Hospital Zurich, Raemistrasse 100, Zurich, CH-8091, Switzerland

2 Department of Radiology, Orthopedic University Hospital Balgrist, Forchstrasse 340, Zurich, CH-8008, Switzerland

3 Division of Biostatistics, Institute for Social and Preventive Medicine, University of Zurich, Hirschengraben 84, Zurich, CH-8001, Switzerland

4 Department of Rheumatology, University Hospital Zurich, Raemistrasse 100, Zurich, CH-8091, Switzerland

For all author emails, please log on.

EJNMMI Research 2012, 2:38 doi:10.1186/2191-219X-2-38

Published: 12 July 2012

Abstract

Background

This study compares the frequency and distribution of increased activity on 18 F-fluoride PET/CT with the presence of bone marrow edema on whole-body MR imaging in the spine and sacroiliac joints (SIJ) of patients with active ankylosing spondylitis (AS).

Methods

Ten patients (6 men and 4 women), between 30 and 58 years old (median 44) with active AS, were prospectively examined with both whole-body MRI and 18 F-fluoride PET/CT. Patients fulfilled modified NY criteria and had a Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) of at least 4. Increased radiotracer uptake in PET/CT and bone marrow edema in whole-body MRI of spine and SIJ was evaluated independently by two blinded observers for each modality. Kappa statistics were used to compare interobserver agreement as well as scores of consensus reading of the two imaging modalities.

Results

Analysis of interobserver agreement for PET/CT yielded a kappa value of 0.68 for spinal lesions and of 0.88 for SIJ lesions. The corresponding kappa values for the MRI modality were 0.64 and 0.93, respectively. More spinal lesions were detected by MRI in comparison to PET/CT (68 vs. 38), whereas a similar number of SIJ quadrants scored positive in both modalities (19 vs. 17). Analysis of agreement of lesion detection between both imaging modalities yielded a kappa value of only 0.25 for spinal lesions and of 0.64 for SIJ lesions.

Conclusion

Increased 18 F-fluoride uptake in PET/CT is only modestly associated with bone marrow edema on MRI in the spine and SIJ of patients with AS, suggesting different aspects of bone involvement in AS.

Keywords:
18F-fluoride PET/CT; Whole-body MRI; Ankylosing spondylitis; Syndesmophytes; Inflammation