The value of ¹⁸F-FDG PET/CT dual-phase imaging in the differential diagnosis of osteolytic lesions

Objective To evaluate the diagnostic value of metabolic parameters derived from dual-phase ¹⁸F-FDG PET/CT imaging in differentiating osteolytic metastases from multiple myeloma (MM).

Methods A retrospective analysis was conducted on 50 patients with osteolytic metastases 29 males, 21 females; age 56.8±12.8 years(range 15–80) and 37 patients with MM 22 males, 15 females; age 58.5±8.5 years (range 37–77) confirmed by histopathology or clinical follow-up at Chifeng Municipal Hospital from September 2019 to June 2022. Dual-phase imaging included conventional (early-phase) PET/CT scans 50–60 min post-injection and delayed-phase scans 110–120 min post-injection for lesions with higher metabolism or larger size. On a per-patient basis, the maximum standardized uptake value (SUV_max) of the primary tumor and the most metabolically active osteolytic metastatic lesion was measured in both early and delayed phases. On a per-lesion basis, the SUV_max of up to three lesions with the highest metabolic activity was assessed in both phases. The same measurement protocol was applied for MM.The retention index (RI) was calculated. Differences in metabolic parameters between the two groups were analyzed using the Mann-Whitney U test, while lesion distribution differences were assessed using the chi-square test. ROC curve analysis determined the optimal early SUV_max cutoff and diagnostic efficacy for distinguishing the two groups. Spearman correlation analyzed early SUV_max between the highest-metastasis and primary lesions in the osteolytic metastasis group.

Results On a per-patient basis, the early SUV_max of osteolytic metastases 10.85 (8.60, 14.98) was higher than that of MM 4.50 (3.15, 6.10). On a per-lesion basis, osteolytic metastases had a higher early SUV_max 10.10 (7.80, 12.80) than MM lesions 3.50 (2.45, 5.45). The RI of osteolytic metastases 0.17 (0.07, 0.36) was also higher than that of MM −0.01 (−0.17, 0.36), with all differences being statistically significant (z=−6.470、−11.247、−2.576, P<0.05). The optimal early SUV_max cutoff for distinguishing osteolytic metastases from MM was 6.95, with a sensitivity of 83.2%, specificity of 87.2%, and AUC of 0.926 (95% CI: 0.893–0.959) (P<0.001). In the osteolytic metastasis group, SUV_max of metastases and primary lesions showed a moderate positive correlation (*r*=0.66, P<0.001). MM lesions were more frequently distributed in the skull, cervical spine, thoracic spine, and shoulder/clavicle compared to osteolytic metastases (χ²=6.585, 6.842, 4.262, 3.999, P<0.05).

Conclusions Metabolic parameters from dual-phase ¹⁸F-FDG PET/CT offer significant value in the differential diagnosis of osteolytic metastases and MM.