Impaired Tc-99m MIBI uptake in the thyroid and parathyroid glands during early phase imaging in hemodialysis patients.

The purpose of this study is to evaluate the possible reasons of an observation of diminished uptake of Tc-99m MIBI in the early phase of parathyroid scintigraphy in the thyroid and parathyroid glands in patients with chronic renal failure who are being evaluated for hyperparathyroidism. Fourteen patients with secondary hyperparathyroidism all on hemodialysis with supplement therapy consisting of mainly vitamin D and calcium carbonate were studied. Neck and mediastinum images obtained at early and late phases were evaluated both visually and semiquantitatively. Patients with high PTH levels on hemodialysis showed diminished accumulation of radioactivity in the thyroid glands in the early phase compared to the soft tissue with a ratio of 1.54 +/- 0.39 (mean +/- std). A control group consisting of 10 patients with osteoporosis and Rickets' disease on vitamin D therapy was taken as control group A, as well as 11 patients with no problems other than cardiac who were not on any medication as control group B and 8 patients on hemodialysis only with normal PTH levels as control group C. Patients in control group A and C showed diminished accumulation of radioactivity in the thyroid glands in the early phase compared to the soft tissue with a ratio of 1.57 +/- 0.43 and 1.34 +/- 0.13, respectively, while patients in control group B showed good uptake 3.18 +/- 0.43. None of the studies showed parathyroid pathology. The results of this study show that patients with chronic renal failure under hemodialysis treatment are prone to show decreased uptake of the radioactivity. Another finding is that vitamin D supplements can cause diminished uptake of Tc-99m MIBI. A possible explanation is mentioned in the literature by an increase in PGP level and multi-drug resistance, so we suggest that it may play a role in impaired Tc-99m MIBI uptake in the thyroid phase and recommend cessation of vitamin D3 metabolites before performing parathyroid scintigraphy.