To investigate the regularity and clinical significance of abnormal bone uptake of ⁹⁹Tc^m-methylene bisphosphonate (MDP) in benign and malignant lesions.

A retrospective analysis was performed on 266 patients (132 males, 134 females, age range: 8-85 years) with abnormal uptake of ⁹⁹Tc^m-MDP in extraosseous tissues from September 2015 to March 2018. The final diagnosis of abnormal uptake was made according to the histopathology, laboratory and related imaging examination (CT, MRI, ultrasound, SPECT/CT or PET/CT imaging) results within 2 weeks after ⁹⁹Tc^m-MDP imaging. Regularity of abnormal ⁹⁹Tc^m-MDP uptake was comprehensively analyzed. Differences between benign and malignant groups were compared by χ² test or Fisher exact test.

Abnormal ⁹⁹Tc^m-MDP uptake in extraosseous tissues in 232 patients (87.2%, 232/266) were confirmed as malignant lesions and those in 34 patients (12.8%, 34/266) were benign. There were no significant differences in gender (χ²=0.611, P>0.05), age (P=0.584), and location (P=0.118) between benign and malignant lesions, but the involvement was significantly different (χ²=19.515, P<0.05). There were significant differences between single focus and diffuse foci of single organ, diffuse foci of single organ and multiple foci groups (χ²=8.959, 19.325, both P<0.01).

The detection rate of malignancy among foci with abnormal ⁹⁹Tc^m-MDP uptake in extraosseous tissues is high, and the malignancy may relate with the involvement of foci. When extraosseous uptake is found, clinical information and related examination results should be comprehensively analyzed and the malignancy should be taken into account.

Skeleton; Neoplasms; Diagnosis, differential; Tomography, emission-computed, single-photon; Tomography, X-ray computed; Technetium Tc 99m medronate