Potential of 99mTc-MIBI for detecting bone marrow metastases

In this study, we evaluated the potential of Tc-99m-hexakis-2-methoxyisobutylisonitrile (MIBI) for detecting bone metastases in comparison with a conventional bone tracer. Methods: Tc-99m-MIBI and Tc-99m-hydroxymethylene diphosphonate (HMDP) scans were obtained from 99 patients with proven malignant diseases and suspected bone metastases. We compared 373 lesions that showed abnormal uptake on Tc-99m-MIBI scans or Tc-99m-HMDP scans (or both). Results: Bone metastases were confirmed in 334 of 373 lesions. Thirty-nine lesions on Tc-99m-HMDP scans had false-positive findings, but only 2 of these lesions had false-positive findings on Tc-99m-MIBI scans. Tc-99m-MIBI and Tc-99m-HMDP scans were equivalent in 168 of 334 lesions (50.3%). Tc-99m-MIBI scans correctly detected more lesions than Tc-99m-HMDP scans: 284 lesions (85.0%) versus 218 lesions (65.3%) (P < 0.005), respectively. Tc-99m-MIBI scans showed a markedly higher sensitivity for detecting metastases in the femur and humerus compared with Tc-99m-HMDP scans: 97 of 98 lesions (99.0%) versus 35 of 98 lesions (35.7%) (P < 0.005) and 21 of 22 lesions (95.5%) versus 11 of 22 lesions (50.0%) (P < 0.005), respectively. Tc-99m-HMDP scans of 17 patients showed no abnormal images. However, Tc-99m-MIBI scans correctly detected bone metastases, and subsequent development of multiple lesions was observed on follow-up Tc-99m-HMDP scans of 15 patients. Tc-99m-MIBI scans were superior to Tc-99m-HMDP scans in the detection of metastases attributed to breast cancer, multiple myeloma, and hepatoma. On the contrary, Tc-99m-MIBI scans were less sensitive than Tc-99m-HMDP scans for detecting bone metastases attributed to prostate cancer in the other skeletal sites except for femur and humerus. Conclusion: Tc-99m-MIBI scans have better sensitivity for detecting bone metastases and provide more specific complementary findings than conventional bone scans. Tc-99m-MIBI accumulation attributed to bone marrow metastases may occur at an early stage, before the bone remodeling process in the surrounding bone can be detected on conventional bone scans.