194 Part II Chapter 8 presumably due to alternating denosumab dosing due to concomitant inflammatory bowel disease and infliximab treatment. For the total denosumab group including this patient, the median (IQR) decrease of FTV equaled 60% (-70% to -15%) as this single patient had only limited effect on median FTV decrease. ∆FTV between the denosumab group and non-denosumab group did not differ significantly, p=0.064. Within the non-denosumab group, the FTV-decrease did still not significantly change (p=0.249), median ∆FTV of 23%, in contrast to the patients treated with denosumab median ∆FTV of 61% (p=0.018). Initial FD-burden as measured by FTV on baseline Na[18F]F PET-CT in patients treated with denosumab was significantly higher (median 361 cm3 and thus indicating higher FD-burden) than in non-denosumab users (median 76 cm3, p=0.005;), Figure 3. Figure 3. FTV on Na[18F]F PET-CT scans at baseline and during follow-up in the denosumab and non-denosumab group. It is noted that initial FTV is significantly higher in patients starting denosumab in comparison to the non-denosumab group. FTV decreased significantly in the denosumab and did not decrease in the non-denosumab group.