A novel assessment of Tc-99m-diphosphonate bone scan quantification in fibrous dysplasia using a combined planar and SPECT/CT analysis

Purpose: Bone scintigraphy with Tc-99m-labeled diphosphonate can identify fibrous dysplasia (FD), which typically exhibits markedly increased tracer uptake. The aim of this study was to investigate the emerging role of Tc-99m DPD uptake quantification in FD lesions in correlation with markers of disease activity. MATERIALS AND METHODS:We retrospectively assessed 8 patients (49±15y) with a biopsy-confirmed FD diagnosis. Quantitative SPECT/CT images (xSPECT/CT) were performed (Symbia Intevo, Siemens Healthineers). SUV_max and SUV_mean were measured in all bone lesions. Skeletal burden score (SBS) was assessed on planar scintigraphy for all patients and SBS_SUV_max and SBS_SUV_meanwas generated by multiplying SBS by SUV_max and SUV_mean, respectively. Planar and xSPECT/CT quantification outcomes were correlated with markers of disease activity, including: Procollagen 1 Intact N-Terminal Propeptide (P1NP), Fibroblast growth factor 23 (FGF-23) and Alkaline phosphatase (ALP).

Results: A total number of 77 FD bone lesions were analyzed, showing a median (95% CI) SUV_max and SUV_mean (g/mL) of 10.1 (9-13) and 6.2 (5.3-7.9), respectively. SBS, SBS_SUV_max and SBS_SUV_mean values were 22.3 (0.1-64.8), 378.6 (0.8-748.9) and 234.6 (0.5-463.5), respectively. Mean measured values of P1NP (microg/L), FGF-23 (pg/ml) and ALP (U/L) were 100 (31-1161), 91.7 (22.1-175) and 272 (46-735), respectively.We found a very strong positive correlation between planar derived SBS and ALP (r=0.82, p=0.024). SBS_SUV_max and SBS_SUV_mean also showed a very strong positive correlation with both ALP (r=0.88, p=0.008; and r=0.88, p=0.008) and P1NP (r=0.78, p=0.037; and r=0.79, p=0.036). No correlation was found between measured bone scan quantification outcomes and FGF-23.

Conclusions: This study shows a significant correlation between biological bone turnover factors and diphosphonate uptake on bone scan quantified using both planar and SPECT/CT scans. Therefore, further analysis of bone scan quantitative SPECT/CT data can help better characterize FD bone lesions and may help in guiding patient management.