Role of Tc99m sestaMIBI SPECT in optimizing the localization of over-functioning parathyroid glands in hyperparathyroid patients

Objectives Hyperparathyroidism, especially primary forms is a relatively common endocrine disorder. Different methodologies were utilized, mainly using planner imaging. SPECT affords accurate parathyroid abnormalities localization in the neck or ectopic places with better delineation from thyroid or background activities. Aim: evaluation of clinical role of Tc99m sestaMIBI SPECT for better localization of overfunctioning parathyroids in Hyperparathyroid subjects.

Methods Ninety (90) patients clinically presenting with diffuse bony aches & muscle weakness with biochemically confirmed hyperparathyroid status [mean age 32.9y±15.53, 10/90 (11.1%)♂ & 80/90 (88.9%)♀] were allocated in this study for planner (single tracer/dual phase) and SPECT (elliptical orbit, 60×2 steps, 30 second/step, 128×128 Matrix) imaging after IVI of 550 MBq of Tc99m sestaMIBI. The positive cases were surgically explored.

Results [78/90(86.7%)] & [73/90(81.1%)] were negative and 12/90(13.3%) & 17/90(18.9%) were positive by the planner and SPECT respectively [11/17(64.7%) adenoma (5 superior and 6 inferior) & 1/17(5.9%) four gland hyperplasia] according to the strict criteria. The 5/17(29.4%) additionally diagnosed cases on SPECT were ectopic (mediastinal & upper cervical). The mean (PTH) was higher in positives compared to negatives (1225.8 vs. 379.8, P=0.003). Receiver operator characteristics analysis defined PTH of 600 mg/dl as an optimal cut off point (COP) for positive scan prediction (83.3 sensitivity, 85.5 specificity & P<0.001), with 14/2(58.3%) cases above while 3/66(4.5%) below (COP) were scintigraphically positive.

Conclusions SPECT is having an adding diagnostic value in accurate localization of over-functioning parathyroid(s), especially ectopic ones, in clinically suspected cases. In addition, 600mg/dl PTH is suggested as a (COP), where about 60% likelihood for scan positivity is predicted above it