Abstract
Objectives: This study aims to assess the relation between Tc-99m sestamibi parathyroid scan (PS) imaging findings and serum levels of parathormon (PTH) and calcium (Ca) in patients with hyperparathyroidism. Methods: We retrospectively included 57 consecutive patients with hyperparathyroidism (average age of 45.7±13.96 years; 41 (72%) females). All patients underwent PS with early (30 minutes) and delayed (3 hours) phases. SPECT/CT was performed for 43 patients (75%). The Data collected included patients' demographics, parathyroid hormone (PTH) levels, PS findings, ultrasound (US) findings, surgical and pathological findings. For positive-negative classification of PS results, equivocal results were counted with the positive group. We used Student T-test to compare mean values of continuous variables between subgroups. Chi-square test was used to compare the frequency of categorical variables between study groups. ROC analysis was used to define the cutoff for PTH or Ca levels that best differentiate positive from negative scans. Results: From the 57 patients 27 had secondary and 30 had primary hyperparathyroidism. Serum PTH was higher and Ca level was lower in those with secondary hyperparathyroidism (190.8±115.3 vs 37.8 ±49.1 pmol/l; p<0.0001) and (2.27±0.28 vs 2.63±0.71 mmol/l; p=0.022) respectively. There were 42 (74%) patients with positive and 15 (26%) with negative PS. All 27 patients (100%) with secondary hyperparathyroidism had positive PS results while only 15out of 30 (50%) with primary hyperparathyroidism were positive. Histopathological results were available for 18 patients of whom 15 had adenomas and 3 had hyperplasia. The serum PTH ranged from 1.3 to 428 pmol/l (average 110.3 pmol/l ± 115.6). Serum Ca level ranged from 2 to 6 mmol/l (average 2.46 ± 0.58 pmol/l). The PTH was higher in positive scan group (142.0±118.5 vs 21.5±29.3; p<0.0001). A PTH of ˃35 pmol/l was the best cutoff value to differentiate +ve from -ve PS with sensitivity, specificity, PPV, NPV and accuracy of 73.8%, 93.3%, 96.9%, 56.0% and 77.2% respectively (p=0.0001). No significant difference in Ca level was noted between both groups. However in the subgroup with primary hyperparathyroidism serum Ca level was significantly higher in those with positive PS (2.89±0.9 vs 2.37±0.31; p<0.048) and a Ca level of ˃2.4 mmol/l was the best cutoff value to differentiate +ve from -ve PS with sensitivity, specificity, PPV, NPV and accuracy of 73.3%, 66.7%, 68.7%, 71.4% and 70.0% respectively (p=0.028). From 44 patients who had US, 28 were positive and 16 were negative. No significant difference in PTH or Ca levels were found between those with positive or negative US. The number of visualized parathyroid gland on PS were correlated to PTH level (r=0.476; p<0.001). Conclusions: Tc-99m MIBI parathyroid scan findings are closely correlated to PTH level in both primary and secondary hyperparathyroidism as well as Ca level in primary hyperparathyroidism subgroup. A cutoff value of PTH of ˃35 pmol/l was the best cutoff values to predict a positive PS in the entire study population.