Background: Criteria for diagnosing primary hyperparathyroidism (PHPT) include hypercalcemia in the presence of parathyroid hormone (PTH) levels that are either elevated (classic PHPT) or normal but non-suppressed. However, there is no standard definition of what constitutes normal non-suppressed levels, and data are lacking regarding the potential for surgical cure in these patients.
Methods: A retrospective review of patients undergoing parathyroidectomy for sporadic PHPT between 2012 and 2014 was performed. Patients with normal PTH were compared to classic PHPT patients to assess demographics, imaging, operative findings, and outcomes.
Results: In total, 332 patients met study criteria, and 60 (18%) had normal PTH levels. Negative sestamibi scans were seen more often with normal PTH levels (18.3 vs. 4.8%, p < 0.001). Patients with normal PTH were more likely to have ≥2 glands removed (26.7 vs. 14.3%, p = 0.02), and the specimens were more likely to be classified as only mildly hypercellular or normocellular (20 vs. 2.9%, p < 0.001). Average follow-up was 24 months (range 6-55). Cure rate was 88% in the normal PTH group, compared to 96% in classic PHPT (p = 0.02). Among patients with normal PTH, those with PTH ≤ 55 pg/mL had an 83% cure rate, whereas those with PTH 56-65 had a 96% cure rate (p = 0.12).
Conclusions: Parathyroidectomy can have a high cure rate in the context of normal PTH levels despite an increased likelihood of negative imaging and multigland resection. Operative success is equivalent to classic PHPT when PTH levels are > 55 pg/mL.