Limited sensitivity of parathyroid imaging with (99m)Tc-sestamibi/(123)I subtraction in an endemic goiter area.

UNLABELLED Double-phase single-tracer scintigraphy with (99m)Tc-sestamibi is now generally used for parathyroid imaging but, at least in endemic goiter areas, complementary thyroid scintigraphy is recommended. Although (123)I-sodium iodide is considered to be the optimal thyroid agent, it is hardly ever used because of high costs and logistic difficulties. Our study presents the results of using the (99m)Tc-sestamibi/(123)I subtraction technique in a region with a high goiter prevalence. Special attention was paid to the changes in sensitivity and specificity and their relationship to thyroid volume as well as to autonomous and nodular thyroid disease. METHODS One hundred three scintigraphic parathyroid examinations on 96 patients were included in this study. Fifty-eight of all patients had concomitant morphologic or functional alterations of the thyroid. Initially, 10 MBq (123)I-sodium iodide were injected. Then, 150 MBq (99m)Tc-sestamibi were administered after 3-5 h, followed by planar scintigraphic imaging of the neck and upper chest region using a double-isotope technique. RESULTS An area with increased tracer uptake on the subtraction image was found in 44 cases. Forty-three of them proved to be true-positive. No suspicious lesions were detected scintigraphically on the remaining 59 examinations. However, histologic examination revealed a parathyroid adenoma or hyperplasia in 11 of these cases. The mean parathyroid volume of these false-negative patients was 0.9 mL. Secondary hyperparathyroidism with multiple enlarged parathyroid glands was found in 4 of these cases. The sensitivity of the parathyroid scintigraphy was 80% (43/54) and the specificity was 98% (48/49). There was a distinct difference in the sensitivity between the subgroups with thyroid volumes of >15 mL and <15 mL (76% vs. 88%), although the resected parathyroid glands had a similar size in both subgroups. The specificity was 97% and 100%, respectively. No significant difference in the sensitivity and specificity was observed between the subgroups with and without morphologic or functional alterations of the thyroid (80% vs. 79% and 96% vs. 100%, respectively). CONCLUSION The sensitivity of parathyroid imaging with (99m)Tc-sestamibi/ (123)I subtraction depends mainly on the thyroid and parathyroid volumes rather than on the presence of nodular or autonomous thyroid disease.