Abstract
87
Objectives: 99mTc-labelled sestamibi scintigraphy combined with single photon emission computed tomography (SPECT) has the highest positive predictive value among imaging modalities for localizing hyperfunctioning parathyroid lesions. Sestamibi parathyroid scan is the procedure of choice in primary hyperparathyroidism (pHPT), but sensitivity and specificity are relatively low in secondary hyperparathyroidism (sHPT) and tertiary hyperparathyroidism (tHPT). P-glycoprotein, which accelerates efflux of sestamibi out of the cells in sHPT and tHPT, is thought to be the mechanism demonstrating low uptake and rapid washout. There are studies showing sestamibi uptake in correlation to weight, cellular function, and localization, but there are also others not recommending for sHPT and tHPT. However, hyperparathyroidism related to kidney transplantation (KT) differs in pathophysiology from non-KT patients with hyperparathyroidism. Immunosuppressants can also modify P-glycoprotein expression which affects sestamibi uptake of parathyroid glands. Persistent hyperparathyroidism in KT patients is associated with additional complications and morbidities such as allograft rejection. The objective of this study is to investigate the usefulness of 99mTc sestamibi scintigraphy in persistent hyperparathyroidism after KT.
Methods: Retrospectively evaluated 38 patients who received parathyroidectomy among the 75 patients who had sestamibi parathyroid scan for persistent hyperparathyroidism after KT from Nov. 2013 to Nov. 2020 at a single medical center. Patient features show an average age of 43 years old, sex ratio of 23 males to 15 females, and an average interval period between KT to parathyroidectomy of 1504 days. Parathyroid lesions were analyzed separately according to the four normal anatomical locations or otherwise an ectopic site seen in the sestamibi scan and verified by surgical pathology. A parathyroid lesion with the highest sestamibi uptake intensity of a patient was graded from 0 to 3 (0=none; 1=soft tissue/bone equivalent; 3=below salivary glands; 4=equivalent and above salivary glands). Uptake intensity was analyzed in correlation with parathyroid hormone (PTH), calcium, ionized calcium, phosphorus, and vitamin D.
Results: Per-patient analysis, the vast majority (n=32, 84%) had hyperplasia, five patients had single or double adenomas and one patient had a parathyroid carcinoma. Precise localization of parathyroid adenoma and carcinoma was achieved not by planar images but through SPECT/CT. Only two patients with hyperplasia did not demonstrate any discernable sestamibi uptake in the parathyroid scans. Two other patients showed positive ectopic sites confirmed by pathology in the thymus and left carotid sheath. Out of the 112 pathologically confirmed parathyroid lesions, SPECT/CT images were able to identify 65 lesions (58%) and 50 lesions (45%) just by planar images. Twenty-six patients (68%) showed more than half of the lesions positive in the sestamibi scan. The average of sestamibi uptake intensity grade was relatively low at 1.5. Uptake intensity showed positive correlation with parathyroid hormone (PTH) level but not with phosphorus, calcium, ionized calcium, or vitamin D levels.
Conclusions: Even though sestamibi parathyroid scans show relatively low uptake and lesions are less discrete in KT patients, they still provide useful information that we expect from pHPT. Since not all hyperfunctioning parathyroid lesions are hyperplasia and a non-negligible portion is still adenoma or carcinoma, localization prior to surgery is essential. Detecting ectopic parathyroid lesions is also critical in preoperative assessment.