THE USE OF TC-99M-MIBI SCANNING IN MULTIPLE-MYELOMA

Tc-99m 2 methoxy-isobutyl-isonitrile ((99)mTc-MIBI), also called Sesta mibi, is a safe and effective scanning agent in solid tumours. Its use in imaging lesions in multiple myeloma has been studied in 21 patient s with either multiple myeloma (19/21) or monoclonal gammopathy of und etermined significance (MGUS) (2/21). Tc-99m-MIBI scanning was positiv e in 14 patients, 13 with active myeloma and one patient with MGUS sho wing possible transformation to a more accelerated phase. In seven pat ients Tc-99m-MIBI scanning was negative. In four of them, the result w as unexpected, as they had the features of active myeloma. All four we re either primarily or secondarily resistant to chemotherapy, with hig h total cumulative doses of doxorubicin. Overexpression of P-glycoprot ein associated with multidrug resistance could be a factor, as it has been shown that Tc-99m-MIBI is actively eliminated from the cell by P- glycoprotein. With this assumption, sensitivity of the scanning techni que in this series is 100%, and the specificity 88%. No toxicity was e xperienced by any patient. Tc-99m-MIBI scanning is a useful adjunct to the investigation of multiple myeloma, and may have potential as an i n vivo test for multidrug resistance.