Total Lesion Uptake Ratio of on Tc-99m MIBI Parathyroid SPECT/CT: A Quantitative Marker to Evaluate the Disease Severity of Primary Hyperparathyroidism

Objectives It is important to evaluate disease severity of primary hyperparathyroidism (PHPT) for making decisions not only about the surgical treatment but also for monitoring patients who do not undergo parathyroid surgery. We investigated the relationship between quantitative markers based on Tc-99m MIBI parathyroid SPECT/CT and biochemical markers as well as clinical features in patients with PHPT.

Methods 60 PHPT patients performed three procedures, dual-phase Tc-99m MIBI planar scintigraphy, delayed SPECT/CT, and ultrasonography after treatment with calcitonin were retrospectively enrolled. The pathologic volume (PV) of each lesion was measured following parathyroidectomy. For the 38 patients showed positive scintigraphy and no sign of thyroid nodule by ultrasonography, lesion-to-background ratio (LBR), metabolic volume (MV) and total lesion uptake ratio (TLUR) were measured. Also, their relationship with symptoms, preoperative serum intact parathyroid hormone (iPTH), calcium values before (Ca1) and after (Ca2) calcium-lowering medications were analyzed.

Results 63 lesions were found in 60 patients including 49 single entopic parathyroid adenomas, six multiple parathyroid adenomas, seven parathyroid hyperplasias and one parathyroid carcinoma. The symptomatic PHPT patients (SPP) had significantly higher TLUR than the asymptomatic PHPT patients (ASPP). However, there were no significant differences between the SPP and the ASPP in terms of PV, MV, and LBR values. TLUR was strongly correlated with PV, iPTH, and Ca1. However, LBR, MV, and TLUR were not correlated with Ca2. LBR was significantly correlated with PV and Ca1, but not correlated with serum iPTH.

Conclusions TLUR with a strong correlation with biochemical markers and clinical features appears to be a promising quantitative marker in evaluating disease severity for PHPT patients, especially for ASPP.