Endocrine Abstracts

^99mTc-Sestamibi (SeS) is a standard tool for localization of adenomas/hyperplasia (PA) in hyperparathyroidism (HPTH), designed on the difference between thyroid and parathyroid tissue radiotracer washout on early and late scintigraphy phases. However, PA have been reported to washout as fast as normal thyroid tissue (‘rapid washout’, RW), which may lead to diagnostic failure. The aim of the study was to determine a correlation of RW of SeS from parathyroid glands and types of hyperparathyroidism (HPTH). The utility of dual isotope radiopharmaceutical acquisition with ¹²³I/SeS subtraction imaging (SS) for detection of PA with RW was also investigated.

Methods: An IRB approved retrospective review of cases with HPTH referred to nuclear medicine and had subsequent parathyroid surgery was performed. Pre-, post-surgical and biochemical workup of HPTH, surgical pathology reports were analyzed. Correlative imaging with ¹²³I/SeS subtraction imaging was performed on selective patients. Group comparison was performed using paired t-test, ANOVA, and Brown–Forsythe tests.

Results: 135 HPTH patients after parathyroidectomy with available dual phase SeS, pathology report, pre- and post-surgical biochemical HPTH workup were analyzed. Ninety-six (71%) patients had primary (p-HPTH), 29 (21%) had secondary (s-HPTH) and 10 (7%) had tertiary (t-HPTH) HPTH. 87/103 (84%) in p-HPTH, 53/94 (56%) in s-HPTH, and 16/23 (69%) in t-HPTH glands were positive on late SeS. RW was identified in 27% (28/103) p-HPTH, 15% (14/94) s-HPTH, 4% (1/23) t-HPTH (P<0.0001). Glands that were positive on late SeS phase were large being 1.7 (IQR: 1.4–2.3) vs 1.45 (IQR: 1–2) cm (P=0.0036). Median PTH levels for p-HPTH, s-HPTH, and t-HPTH were 142 (IQR:110–240.3), 955 (IQR:1865–2448), 1394 (IQR: 949–2613) pg/ml respectively (P<0.0001). High PTH levels were associated with early SeS phase positivity (P=0.024) but not with late SeS phase positivity (P=0.26). There was no significant difference in preoperative levels of calcium on retention of SeS radiotracer on early and late phases (P=0.545). Correlative imaging with dual isotope was performed in 17 patients and ¹²³I uptake was positive in 88% of PA with RW.

Conclusion: Higher rates of RW were seen in p-HPTH followed by s-HPTH and t-HPTH and was dependent on PA size but neither on PTH nor calcium levels. Pre-operative PTH levels and size of the gland were major determinants of 99mTc-sestamibi positivity on early SeS phase whereas size is an independent predictor of late SeS phase positivity. SS scintigraphy might be a useful tool in suspected cases of RA.