Objective To explore the application value of metabolic parameters from ¹⁸F-fluorodeoxyglucose (FDG) PET/CT dual-phase imaging in distinguishing between osteolytic metastases and multiple myeloma (MM).

Methods A retrospective analysis was conducted to collect imaging data from 50 patients with osteolytic metastases (29 males, 21 females; mean age (56.8±12.8) years, range 15–80 years) and 37 patients with MM (22 males, 15 females; mean age (58.5±8.5) years, range 37–77 years) who underwent ¹⁸F-FDG PET/CT examinations for osteolytic lesions at Chifeng Municipal Hospital from September 2019 to June 2022 and were ultimately confirmed by biopsy histopathological examination or clinical follow-up. ¹⁸F-FDG PET/CT dual-phase imaging was performed, with routine (early-phase) imaging conducted 50–60 min after radiotracer injection and delayed-phase imaging of hypermetabolic or larger lesions occurring 110–120 min post-injection. In the patient-based analysis, the maximum standardized uptake value (SUV_max) of both early-phase and delayed-phase imaging were measured for the primary lesion and the most metabolically active osteolytic metastatic lesion in the osteolytic metastases group. For lesion-based analysis, the SUV_max of both early-phase and delayed-phase imaging were measured for the three most metabolically active osteolytic metastatic lesions in the osteolytic metastases group. The same measurement methods were applied to the MM group. The retention index (RI) was calculated for both groups. Differences in metabolic parameters and distribution of lesions between the two groups were compared. The Mann-Whitney U test was used to compare measurement data that deviated from the normal distribution between groups. Counting data between groups was compared using the chi-squared test. The receiver operating characteristic (ROC) curve analysis was employed to determine the optimal threshold for early-phase SUV_max to differentiate between osteolytic metastases and MM, and to evaluate diagnostic efficacy. Additionally, a Spearman correlation analysis was performed between the early-phase SUV_max of the most metabolically active metastatic lesion and that of the primary lesion in the osteolytic metastases group.

Results In the patient-based analysis, the early-phase SUV_max in the osteolytic metastases group (10.85 (8.60, 14.98)) was significantly higher than that in the MM group (4.50 (3.15, 6.10)). Similarly, in the lesion-based analysis, the early-phase SUV_max for lesions in the osteolytic metastases group (10.10 (7.80, 12.80)) was higher than that in the MM group (3.50 (2.45, 5.45)). Additionally, the RI in the osteolytic metastases group (0.17 (0.07, 0.36)) was higher than that in the MM group (−0.01 (−0.17, 0.36)), with all differences being statistically significant (Z=−6.470, −11.247, −2.576; all P<0.05). The optimal threshold of early-phase SUV_max for distinguishing osteolytic metastases from MM was 6.95, with a sensitivity of 83.2%, specificity of 87.2%, and an area under the curve of 0.926 (95%CI: 0.893–0.959, P<0.001). A moderate positive correlation was found between the early-phase SUV_max of the metastatic lesion and the primary lesion in the osteolytic metastases group (r=0.66, P<0.001). The distribution of lesions showed that MM was more commonly observed in the cranial bones, cervical vertebrae, thoracic vertebrae, and clavicles, with statistically significant differences in involvement rates between the two groups (χ²=3.999–6.842; all P<0.05).

Conclusion The metabolic parameters obtained from ¹⁸F-FDG PET/CT dual-phase imaging offer good application value in distinguishing between osteolytic metastases and MM.