Use of ^99mTc-Sestamibi Scintigraphy in Multiple Myeloma

TO THE EDITOR: We read with great interest the excellent review on imaging of malignant bone involvement by Einat Even-Sapir published in the August issue of The Journal of Nuclear Medicine (1). We would like to comment on the use of ^99mTc-sestamibi in multiple myeloma. In recent years, different groups have reported a high accuracy for this tracer in the detection of active disease (2–7). In particular, ^99mTc-sestamibi scintigraphy has shown a positive predictive value of 100% and a negative predictive value of 83% in the diagnosis of active multiple myeloma and a positive predictive value of 84% and a negative predictive value of 100% in identifying advanced stages (i.e., II or III) of disease (2). Positive ^99mTc-sestamibi whole-body results were found in 30% of patients with no evidence of multiple myeloma on a radiologic full skeletal survey, and in the majority (76%), the scintigraphic findings agreed with the subsequent clinical follow-up (3). Moreover, there are consistent published data on the use of ^99mTc-sestamibi in follow-up of patients with multiple myeloma (4–6). In particular, all patients with a negative ^99mTc-sestamibi result at follow-up were actually in disease remission (either complete or partial), whereas 86% of those with a positive ^99mTc-sestamibi result had disease progression (4). Even-Sapir expressed his concern about using ^99mTc-sestamibi in follow-up studies because of the development of multidrug resistance, which may block tracer accumulation (1). In our experience, the multidrug-resistant phenotype is characterized by a faster washout of ^99mTc-sestamibi rather than a lower early tracer uptake (8,9), and washout rates of ^99mTc-sestamibi were indeed predictive of response to chemotherapy in these patients (10). Therefore, when images are acquired 10 min after tracer injection, the diagnostic accuracy of ^99mTc-sestamibi scanning is not significantly affected by P-glycoprotein overexpression, and patients with multiple myeloma can confidently be monitored with ^99mTc-sestamibi scanning after treatment.