Absent ^99mTc-MIBI Uptake in the Thyroid Gland during Early Phase of Parathyroid Scintigraphy in Patients with Primary and Secondary Hyperparathyroidism

Background: Thyroid uptake of technetium-99m methoxyisobutylisonitrile (^99mTc-MIBI) during parathyroid scintigraphy can be affected by various conditions.

Aim: To evaluate the frequency of absent ^99mTc-MIBI uptake by the thyroid gland in the early phase of dual-phase parathyroid scintigraphy.

Methods: The early planar images of dual phase Tc^99m MIBI parathyroid scintigraphy from 217 patients performed between 2014 and 2017 were retrospectively analysed. Patients were divided into two groups. The first group included 147 patients with primary hyperparathyroidism and the second group included 70 patients with chronic renal failure. Patient records, laboratory and ultrasonographic data were analysed in all patients. Descriptive statistic was used for data analysis.

Results: Out of all patients in the first group, 18 patients (12.24%) showed absent thyroid uptake. Thyroidectomy was performed in 44.4% of these patients, and the rest of them had some thyroid disease. Only one patient had no thyroid or another chronic disease. In the second group, 8 patients (11.42%) presented with absent thyroid uptake of MIBI. Among them, 5 patients had no history of thyroid disease and had been on hemodialysis programme, and 3 patients had hypothyroidism.

Conclusion: Absent ^99mTc-MIBI uptake in the thyroid during the early phase of parathyroid scintigraphy is most frequently related to thyroid disease. A small proportion of patients with chronic renal failure can present with absent ^99mTc-MIBI uptake in the thyroid as well. The mechanism for this alteration is still unclear and needs further investigation.