A Multimodal Imaging Protocol, ¹²³I/⁹⁹Tc-Sestamibi, SPECT, and SPECT/CT, in Primary Hyperparathyroidism Adds Limited Benefit for Preoperative Localization

Introduction: Focused parathyroidectomy in primary hyperparathyroidism (1°HPT) is possible with accurate preoperative localization and intraoperative PTH monitoring (IOPTH). The added benefit of multimodal imaging techniques for operative success is unknown. Method: Patients with 1°HPT, who underwent parathyroidectomy in 2012-2014 at a single institution, were retrospectively reviewed. Only the patients who underwent the standardized multimodal imaging workup consisting of ¹²³I/⁹⁹Tc-sestamibi subtraction scintigraphy, SPECT, and SPECT/CT were assessed. Results: Of 360 patients who were identified, a curative operation was performed in 96 %, using pre-operative imaging and IOPTH. Imaging analysis showed that ¹²³I/⁹⁹Tc-sestamibi had a sensitivity of 86 % (95 % CI 82-90 %), positive predictive value (PPV) 93 %, and accuracy 81 %, based on correct lateralization. SPECT had a sensitivity of 77 % (95 % CI 72-82 %), PPV 92 % and accuracy 72 %. SPECT/CT had a sensitivity of 75 % (95 % CI 70-80 %), PPV of 94 %, and accuracy 71 %. There were 3 of 45 (7 %) patients with negative sestamibi imaging that had an accurate SPECT and SPECT/CT. Of 312 patients (87 %) with positive uptake on sestamibi (93 % true positive, 7 % false positive), concordant findings were present in 86 % SPECT and 84 % SPECT/CT. In cases where imaging modalities were discordant, but at least one method was true-positive, ¹²³I/⁹⁹Tc-sestamibi was significantly better than both SPECT and SPECT/CT (p < 0.001). The inclusion of SPECT and SPECT/CT in 1°HPT imaging protocol increases patient cost up to 2.4-fold. Conclusion: ¹²³I/⁹⁹Tc-sestamibi subtraction imaging is highly sensitive for preoperative localization in 1°HPT. SPECT and SPECT/CT are commonly concordant with ¹²³I/⁹⁹Tc-sestamibi and rarely increase the sensitivity. Routine inclusion of multimodality imaging technique adds minimal clinical benefit but increases cost to patient in high-volume setting.