Normocalcemic primary hyperparathyroidism: 99mTc SestaMibi SPECT/CT results compare with hypercalcemic...

Normocalcemic primary hyperparathyroidism (nPHPT) is defined by an inappropriately increased serum PTH with normal serum calcium. Information about the diagnostic yield of parathyroid SPECT/CT scan and ultrasonography in nHPPT is limited and not conclusive.

To evaluate the positivity rate of ^99m Tc-Sestamibi SPECT/CT scan in nPHTP compared with classical hypercalcemic PHPT (cPHPT).

We retrospectively studied 125 patients with ^99m Tc-Sestamibi SPECT/CT scans. Subjects were divided into 2 groups: cPHPT (n = 93) and nPHPT (n = 32).

The detection rate of ^99m Tc-Sestamibi SPECT/CT in cPHPT was 86,02% (80/93) and 59.37%, in nPHPT (19/32), p = .003. No significant differences were seen between the SPECT/CT scan and ultrasonography (p = .28) and the agreement was higher in cPHPT than in nPHPT, p = .03. Sensitivity of ^99m Tc-Sestamibi-SPECT/CT was 98% on a per-patient basis (PPV 96%) and 91% on a per-lesion basis (PPV 88%). Glandular size was smaller in nPHPT (mean value 6.8 mm) and it was related only with PTH value.

Localization rate of parathyroid hyperfunctioning tissue with ^99m Tc-Sestamibi SPECT/CT is lower in nPHPT and it is related to a smaller glandular size. However, our study suggests that the positivity rate and sensitivity are nonnegligible by adding SPECT/CT. The reduction in the detection rate in nPHPT could benefit techniques with higher resolution such as ¹⁸ F-Choline PET/CT when the clinical context justifies it.