Denosumab Reduces Lesional Fluoride Skeletal Burden on Na[(18)F]F PET-CT in Patients With Fibrous Dysplasia/McCune–Albright Syndrome

CONTEXT: The correlation between fibrous dysplasia/McCune–Albright syndrome (FD/MAS) skeletal disease burden on Na[(18)F]F positron emission tomography–computed tomography (PET-CT) and serum bone turnover markers (BTMs) was recently described. The effect of treatment on lesional fluoride burden in FD/MAS is unknown. OBJECTIVE: To investigate treatment response measurements in patients with FD/MAS who underwent Na[(18)F]F-PET-CT and treatment with antiresorptives. METHODS: Observational case series at an academic center of expertise for rare bone diseases. Fifteen consecutive patients were observed with FD/MAS with baseline and follow-up Na[(18)F]F-PET-CT parameters of healthy bone and FD lesions, BTMs, and pain scores at start of denosumab (n = 8) treatment and non-denosumab patients (n = 7). On Na[(18)F]F-PET-CT the volumetric measures of FD burden (fluoride tumor volume [FTV]) and “fraction affected skeleton” (FAS) represented the portion of the skeleton affected. This was correlated with BTMs and pain. RESULTS: Disease activity decreased significantly, with FTV 361 cm(3) to 97 cm(3) (P = .018) in denosumab-treated patients, but not in non-denosumab patients (P = .249). Serum P1NP and alkaline phosphatase (ALP) decreased significantly: 82 ng/mL vs 55 ng/mL (P = .023) and 119 IU/L vs 84 IU/L (P = .020), respectively. In denosumab-treated patients pain scores improved leading to pain medication reduction. This correlated with lesional uptake, but healthy bone activity did not change. BTMs and FTV correlated positively (P1NP r = 0.730, P < .001; and ALP r = 0.406, P = .006), as did change in BTMs and FTV: P1NP (P = 0.032) and ALP (P = 0.024). FAS strongly correlated with treatment-induced decrease in ALP (P = .027) and P1NP (P = .009). CONCLUSION: Na[(18)F]F-PET-CT captured treatment-induced lesional changes which correlated with BTMs and pain reduction. Therefore Na[(18)F]F-PET-CT can be used as an objective local parameter of response to denosumab treatment in FD/MAS.