Imaging of metastatic medullary carcinoma of the thyroid with 131I-meta-iodobenzyl guanidine.

The uptake of 131I-MIBG by medullary carcinoma of the thyroid was studied in six patients after total thyroidectomy in whom persistent raised plasma calcitonin levels were indicative of residual disease. The only patient in whom any activity in a possible metastasis was seen had by far the highest level of circulating calcitonin of the group and in contrast one patient with a presumptive metastatic deposit showed no uptake of MIBG into it. In conclusion the uptake of 131I-MIBG by medullary carcinoma of the thyroid is unreliable and unpredictable.