Clinical value of Tc-MIBI scintigraphy combined with posttherapeutic I whole-body scanning in patients with differentiated thyroid cancer with sTg ≥10 ng/mL before initial radioiodine therapy: a retrospective study.

[BACKGROUND] The 2015 American Thyroid Association (ATA) guidelines indicate that patients with stimulated thyroglobulin (sTg) ≥10 ng/mL may need further evaluations. It has been reported that Technetium--methoxyisobutylisonitrile (Tc-MIBI) scintigraphy offers a reliable and easy means of detecting metastases in patients with differentiated thyroid cancer (DTC). The principal aim of this study was to investigate the clinical value of Tc-MIBI scintigraphy combined with posttherapeutic I-whole-body scanning (pt-I WBS) in patients with DTC and sTg ≥10 ng/mL before initial radioactive iodine therapy (RAIT). Additionally, we analyzed the differences in the therapeutic efficacy of RAIT among different groups.

[METHODS] In this study, 195 patients with DTC with sTg ≥10 ng/mL before initial RAIT were enrolled. The images of Tc-MIBI scintigraphy and pt-I WBS were then divided into four groups as follows: group 1, Tc-MIBI scintigraphy positive and pt-I WBS positive; group 2, Tc-MIBI scintigraphy negative and pt-I WBS positive; group 3, Tc-MIBI scintigraphy positive and pt-I WBS negative; and group 4, Tc-MIBI scintigraphy negative and pt-I WBS negative. The response to RAIT was classified as excellent response (ER), indeterminate response (IDR), biochemical incomplete response (BIR), and structural incomplete response (SIR) according to the 2015 ATA guidelines. The efficacy of RAIT in different groups was further analyzed.

[RESULTS] The diagnostic sensitivity (χ=55.442; P<0.001), specificity (χ=5.482; P=0.019), positive predictive value (χ=17.306; P<0.001), and negative predictive value (χ=21.926, P<0.001) of Tc-MIBI scintigraphy were lower than those of pt-I WBS in detecting structural or functional disease overall. However, for bone metastasis, we found that Tc-MIBI scintigraphy and pt-I WBS had similar diagnostic efficacy (all P values >0.05). The difference in response to RAIT between group 4 and group 2 (P<0.001) and between group 4 and group 1 (P<0.001) was significant. However, in terms of distant metastasis and local metastasis, the only significant difference was between group 1 and group 4 (F=6.925; P=0.015).

[CONCLUSIONS] Tc-MIBI scintigraphy before RAIT combined with pt-I WBS may be a useful diagnostic tool for the early identification of distant metastasis and poorer response to RAIT in patients with DTC. Moreover, Tc-MIBI scintigraphy before RAIT plays an equally vital role to that of pt-I WBS in patients with DTC with bone metastasis. It may lead to the early detection of bone metastasis before RAIT and guide clinical management.