We studied the usefulness of ^Tc-methoxyisobutyl isonitrile (MIBI) scintigraphy in the detection of bone metastases and in evaluation of therapeutical response to ^I-Na in three patients with differentiated thyroid cancer. On ^Tc-MIBI scintigraphy, increased accumulations were observed in all bone metastatic lesions (14 lesions), whereas on bone scintigraphy using ^Tc-hydroxymethylene diphosphonate (^Tc-HMDP) both increased (eight lesions, 57%) and decreased (six lesions, 43%) accumulations were observed. Within two months after ^I-Na treatment, all 14 lesions were unchanged on bone scintigraphy. However, on ^Tc-MIJBI scintigraphy, disappearance of uptake (six lesions, 43%) and decreased uptake (seven lesions, 50%) were observed in 13/14 lesions (93%). Therefore, ^Tc-MIBI scintigraphy was useful not only in the detection of bone metastatic lesions but also in evaluation of the therapeutical response to ^I-Na in differentiated thyroid cancer
