Endocrine Abstracts

Introduction: Primary hyperparathyroidism is a common endocrine disorder, surgery is curative. Patients with severe hypercalcemia receive cinacalcet or intravenous bisphosphonates as bridging. Intra-operative-parathyroid-hormone (IOPTH) measurement improves surgical accuracy. Bisphosphonates may increase PTH, while cinacalcet reduces it. The main aim was to assess the effect of zoledronate and cinacalcet on IOPTH.

Method: Patients over 15-yo who underwent surgery between 2018-2022 for non-cancerous-single-gland enlargement were retrospectively selected through a prospectively maintained data-base at University-College Hospital, London. The magnitude of IOPTH drop was defined as a percentage at post-excision 5,10,15 minutes, relative to the highest pre-excision value.

Results: Total of 153 were included, 16 were excluded due to missing IOPTH values. Fifteen received zoledronate pre-operatively. 11 had cinacalcet in which four were also given zoledronate. Comparisons were made between the zoledronate only (n=15) vs non-treatment group (n=111) and cinacalcet (n=11) vs non-treatment-group. There was no significant difference between the IOPTH-percentage-drop in the zoledronate and non-treatment groups (Table). The number of patients who achieved at least 50% drop at 5 minutes was not significantly different. The IOPTH-percentage-drop at all time points was significantly higher in the cinacalcet group compared to the non-treatment group (Table), but no significant difference in the number of patients who achieved at least a 50% drop at 5 minutes. 133 of 137 were proven cured at three months while four had no three-month data.

Conclusion: Pre-operative treatment with cinacalcet, but not zoledronate gave rise to significantly higher IOPTH-percentage-drops but had no effect on the surgical outcomes. The small numbers, and overlapping treatments are limitations. This important finding warrants further evaluation through larger studies to assess implications of pre-operative cinacalcet on IOPTH measurements.