• Bruijnen Stefan T G STG Department of Rheumatology, VU University Medical Center, Amsterdam, The Netherlands., Nicki J F Verweij, Leonie M van Duivenvoorde, Nathalie Bravenboer, Dominique L P Baeten, Christiaan J van Denderen, Irene E van der Horst-Bruinsma, Alexandre E Voskuyl, Martijn Custers, Peter M van de Ven, Joost C J Bot, Bouke J H Boden, Adriaan A Lammertsma, Otto S H Hoekstra, Raijmakers Pieter G H M PGHM Department of Radiology and Nuclear Medicine, VU University Medical Center, Amsterdam, The Netherlands., and Conny J van der Laken.
• Department of Rheumatology, VU University Medical Center, Amsterdam, The Netherlands.
• Rheumatology (Oxford). 2018 Apr 1; 57 (4): 631-638.

ObjectivesExcessive bone formation is an important hallmark of AS. Recently it has been demonstrated that axial bony lesions in AS patients can be visualized using 18F-fluoride PET-CT. The aim of this study was to assess whether 18F-fluoride uptake in clinically active AS patients is related to focal bone formation in spine biopsies and is sensitive to change during anti-TNF treatment.MethodsTwelve anti-TNF-naïve AS patients [female 7/12; age 39 years (SD 11); BASDAI 5.5 ± 1.1] were included. 18 F-fluoride PET-CT scans were performed at baseline and in two patients, biopsies were obtained from PET-positive and PET-negative spine lesions. The remaining 10 patients underwent a second 18F-fluoride PET-CT scan after 12 weeks of anti-TNF treatment. PET scans were scored visually by two blinded expert readers. In addition, 18F-fluoride uptake was quantified using the standardized uptake value corrected for individual integrated whole blood activity concentration (SUVAUC). Clinical response to anti-TNF was defined according to a ⩾ 20% improvement in Assessment of SpondyloArthritis international Society criteria at 24 weeks.ResultsAt baseline, all patients showed at least one axial PET-positive lesion. Histological analysis of PET-positive lesions in the spine confirmed local osteoid formation. PET-positive lesions were found in the costovertebral joints (43%), facet joints (23%), bridging syndesmophytes (20%) and non-bridging vertebral lesions (14%) and in SI joints (75%). After 12 weeks of anti-TNF treatment, 18F-fluoride uptake in clinical responders decreased significantly in the costovertebral (mean SUVAUC -1.0; P < 0.001) and SI joints (mean SUVAUC -1.2; P = 0.03) in contrast to non-responders.Conclusions18F-fluoride PET-CT identified bone formation, confirmed by histology, in the spine and SI joints of AS patients and demonstrated alterations in bone formation during anti-TNF treatment.

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