Endocrinol Metab.  2021 Apr;36(2):351-358. 10.3803/EnM.2020.823.

Radioactive Parathyroid Adenomas on Sestamibi Scans: Low Parathyroid Hormone Secretory Potential and Large Volume

Affiliations
  • 1Department of Internal Medicine, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea
  • 2Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea
  • 3Department of Internal Medicine, Seoul Metropolitan Government Seoul National University Boramae Medical Center, Seoul, Korea

Abstract

Background
We investigated the clinical characteristics of parathyroid adenomas according to radioactivity on 99mTc-methoxyisobutylisonitrile (99mTc-MIBI) single-photon emission computed tomography/computed tomography (SPECT/CT) in primary hyperparathyroidism (PHPT) patients.
Methods
The study included 217 patients diagnosed with PHPT from 2000 to 2019 at Seoul National University Hospital who underwent 99mTc-MIBI SPECT/CT scans. On SPECT/CT, the radioactivity of parathyroid adenomas was measured as the ratio of the mean radioactivity count of the parathyroid adenoma to that of the contralateral thyroid.
Results
Tumors were localized by MIBI scans in 190 patients (MIBI [+] group) and by ultrasound or parathyroid four-dimensional CT in 27 patients (MIBI [–] group). The mean age was 55 years, and mean body mass index was 23.4 kg/m2. Patients in the MIBI (+) group had higher parathyroid hormone (iPTH) and lower 25-hydroxy vitamin D levels than those in the MIBI (–) group (168.0 pg/mL [interquartile range, IQR, 111.0 to 250.7] vs. 134.7 pg/mL [IQR, 98.2 to 191.2], P=0.049; 15.4 ng/mL [IQR, 11.1 to 20.8] vs. 21.2 ng/mL [IQR, 13.9 to 24.8], P=0.012, respectively). Patients in the MIBI (+) group had larger tumor volumes, but lower iPTH/volume ratios than those in the MIBI (–) group (1,216.66 [IQR, 513.40 to 2,663.02], 499.82 mm3 [IQR, 167.77 to 1,229.80], P=0.002; 0.18 [IQR, 0.08 to 0.46], 0.40 pg/mL/mm3 [IQR, 0.16 to 1.29], P=0.016, respectively). Adenoma radioactivity was positively correlated with calcium, iPTH, and volume (r=0.180, P=0.020; r=0.208, P=0.006; r=0.288, P<0.001, respectively), but not with iPTH/volume.
Conclusion
Parathyroid adenomas with positive MIBI scans had larger volumes and higher iPTH than adenomas with negative scans, but lower iPTH per unit volume.

Keyword

Hyperparathyroidism; primary; Technetium Tc 99m sestamibi; Parathyroid hormone; Radioactivity
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