R. R. Ayers1, K. Tobin2, D. Elfenbein1, C. J. Balentine1, R. S. Sippel1, H. Chen1, D. F. Schneider1 1University Of Wisconsin,Endocrine Surgery,Madison, WI, USA 2University Of Oregon,Eugene, OR, USA
Introduction: Proper localization is crucial in performing minimally invasive parathyroidectomy for primary hyperparathyroidism (PHPT). Ultrasonography (US) and Tc-99m sestamibi (MIBI) scintigraphy are common methods used for localization. As the appearance and activity of the thyroid gland may impact parathyroid localization, the purpose of this study was to determine how exogenous use of the thyroid hormone, levothyroxine (LT), affects parathyroid localization.
Methods: Adult patients with PHPT who underwent parathyroidectomy from 2001 to 2014 were retrospectively identified from a prospectively collected database. Patients undergoing initial operation without concurrent thyroid surgery or familial hyperparathyroidism were included. Levothyroxine (+LT) and non-levothyroxine (-LT) patients were matched 1:3 based on age, gender, presence of goiter, and pre-operative parathyroid hormone (PTH) levels. Further subgroup analysis was performed on patients previously treated with radioactive iodine (RAI) and patients undergoing single adenoma (SA) resection.
Results: Of the 1,737 patients that met inclusion criteria, 286 were on LT at the time of their localization scan and were matched to 858 –LT patients. There was no difference in gender, age, pre-operative labs, or co-morbidities between the +LT and -LT patients. Use of LT not did significantly impact the percentage of correct MIBI localization scans when compared to -LT patients (p = 0.83). 31 of the 286 +LT patients were post-RAI treatment and this did not impact localization by MIBI either (p = 0.55). Interestingly, use of LT significantly hindered parathyroid localization by US in comparison to the –LT group (48.4 vs 62.2%, p < 0.01) regardless of the reason for LT supplementation (post-RAI: 22.2 vs 67.4 %, p = 0.02). Additionally, for the 73% of patients having SA resection, the percentage of correct US localization was significantly less for +LT when compared to –LT patients (56.7 vs 71.8%, p < 0.01) while MIBI localization accuracy was not significantly different (p=0.31). When examining only patients where a single upper gland was removed, the +LT group was less likely to have a correct US compared to the –LT group (50% vs. 72.8%, p<0.01). There was no difference in percentage of correct US for patients who only had a single lower gland removed (p = 0.51).
Conclusion: Exogenous levothyroxine is associated with impaired parathyroid localization with US but not MIBI. This effect could be due to the thyroid’s echotexture in patients with hypothyroidism limiting the ability to detect more posteriorly located upper glands with US.