Using technetium 99m tetrofosmin parathyroid imaging to detect parathyroid adenoma and its relation to P-glycoprotein expression

Dual-phase 99mTc-MIBI imaging and the expressions of P-gp, GST-π, and MRP1 in hyperparathyroidism

Objective

The aim of this study was to further elucidate the mechanisms of dual-phase technetium-99m methoxyisobutylisonitrile (^99mTc-MIBI) parathyroid imaging by exploring the association between early uptake results (EUR), delayed uptake results (DUR), and the retention index (RI) in dual-phase ^99mTc-MIBI parathyroid imaging and P glycoprotein (P-gp), multidrug resistance-associated protein 1 (MRP1), and glutathione S-transferase-π (GST-π) expression in hyperparathyroidism (HPT).

Patients and methods

Preoperative dual-phase (early and delayed) ^99mTc-MIBI imaging was performed on 74 patients undergoing parathyroidectomy for HPT. EUR, DUR, and RI were calculated. P-gp, MRP1, and GST-π expressions were assessed using immunohistochemistry in resected tissue from HPT and control patients. The association between P-gp, MRP1, and GST-π expressions and EUR, DUR, and RI in HPT was evaluated.

Results

The positive rate of dual-phase ^99mT c-MIBI imaging was 91.89% (68/74) and the false-negative rate was 8.11% (6/74). P-gp and GST-π expressions were higher in tissues resected from control compared with HPT patients (47.37 and 81.5%, P<0.05); there was no difference in MRP1. EUR were associated with P-gp and GST-π expressions, and DUR were associated with MRP1 expression. There was a significant difference in MRP1 expression between RI greater than or equal to 0 and RI less than 0. There was no relationship between the sensitivity of dual-phase ^99mTc-MIBI imaging and P-gp, MRP1, and GST-π expressions in resected parathyroid tissue. The six false-negative HPT cases consisted of three P-gp (−)/MRP1 (−) tissues, three P-gp (−)/GST-π (−) tissues, and four MRP1 (−)/GST-π (−) tissues.

Conclusion

As P-gp and GST-π expressions were higher in tissues resected from control compared with HPT patients, ^99mTc-MIBI may wash out faster from normal parathyroid tissue surrounding the lesion compared with the lesion itself, facilitating detection.

Parathyroid adenoma detected with 99mTc-tetrofosmin dual-phase scintigraphy: a case report

BACKGROUND

Tc-sestamibi is the most frequently used radionuclide agent for the detection of parathyroid adenomas in the clinical setting. However, Tc-tetrofosmin is another such agent that may be used for this purpose. This case report presents the significance and practicality of 99mTc-tetrofosmin for the diagnosis of parathyroid adenomas with probable high p-glycoprotein levels.

CASE PRESENTATION

A 45-year-old woman was referred to our Nuclear Department with a palpable neck nodule suspicious for parathyroid adenoma. She had no significant medical history or other accompanying symptoms. Blood examination results were normal with the exception of the parathormone level which was high at 167.2 pg/ml. Neck ultrasonography revealed a hypoechoic mass near the lower pole of the thyroid gland. 99m Tc-tetrofosmin dual-phase scintigraphy with early and delayed images was performed and the results supported the presupposition of parathyroid adenoma as shown by increased radiopharmaceutical levels near the lower left thyroid gland on the early image that disappeared on the delayed image. Moreover, TcO4- thyroid scintigraphy results excluded thyroid pathology. Two months after the diagnosis, parathyroidectomy was successfully performed without postoperative complications. The pathology report and clinical response to a gradual decrease of parathormone confirmed the initial diagnosis.

CONCLUSION

We strongly recommend the use of reverse 99m Tc-tetrofosmin scintigraphy as a useful and safe examination technique for the diagnosis of parathyroid adenomas.

P-glycoprotein expression is associated with sestamibi washout in primary hyperparathyroidism

Background

The detection of parathyroid adenomas by 99mTc-labelled hexakis 2-methoxyisobutyl isonitrile (sestamibi) scintigraphy is influenced by several factors, including tumour size and serum level of parathyroid hormone (PTH). This study examined the relationship between sestamibi accumulation and multidrug resistance (MDR)-related P-glycoprotein (P-gp) expression in a large series of surgically excised parathyroid tumours.

Methods

Seventy-eight patients underwent dual-phase sestamibi imaging before parathyroidectomy. Expression of P-gp within tumour cells was assessed by immunohistochemistry. Tumour size was measured and the ellipsoid volume calculated. Scan results were analysed in relation to preoperative serum levels of calcium and PTH, P-gp expression and tumour volume.

Results

Sixty-four of the 78 sestamibi scans were positive and 14 negative. Smaller adenomas (less than 0·5 cm3) were more likely to be sestamibi negative than larger lesions (P = 0·006). Ten of 14 adenomas with negative imaging showed strong P-gp membrane positivity and 45 of 64 lesions with a positive scan did not show P-gp membrane expression, indicating a significant association between high P-gp membrane immunoreactivity and negative sestamibi result (P = 0·006).

Conclusion

These data suggest an association between P-gp membrane expression and false-negative sestamibi scan result. Inhibition of the P-gp transmembrane pump using MDR modulators may therefore improve the sensitivity of sestamibi scintigraphy.