MON-768 Impact of Cinacalcet on Bone Mineral Density in Primary Hyperparathyroidism: Therapeutic Effect or Passive Bystander?

Abstract Disclosure: M.S. Varughese: None. L. Varadhan: None. Aim: Primary hyperparathyroidism (PHPT) is associated with an increased risk of fractures. Cinacalcet reduces parathyroid hormone (PTH) and serum calcium levels. However, the effect of cinacalcet on bone mineral density (BMD) in PHPT is not well established and is what this narrative case series aims to explore. Methods: Records of patients with PHPT who were on cinacalcet were reviewed. Patients who had two dual-energy x-ray absorptiometry (DXA) scans and continuous cinacalcet treatment were included. BMD measurement at spine, femoral neck (FN), total hip (TH) and distal 1/3 of forearm (FA) were analysed. Concurrent use of other relevant drugs was also reviewed. Results: 121 patients were commenced on cinacalcet therapy and 44% of these was due to severe hypercalcemia (adjusted Ca ≥3 mmol/L). 11.6% (n=14) had reduced BMD. Of these, 6 had DXA done twice during treatment and were included for review. Indications for cinacalcet use were conservative management only (n=4), failed surgery (n=1), lack of localization and refusal for exploratory surgery (n=1). Of the six patients, three had osteopenia based on BMD of spine, FN or TH (two of these patients had osteoporotic range scores on DXA of the FA which was not detected at any other site).Case 1: Two DXA scans over 4 years and 30 months of cinacalcet therapy. There was marginal improvement of BMD and it remained in the osteopenic range. Case 2: Two DXA scans over 10 years with 63 months of cinacalcet. The BMD progressed from osteopenia to osteoporosis but this was considered to be in keeping with age and duration-related progression. Case 3: Two DXA scans over 7 years but only 8 months of cinacalcet; continued to have stable osteopenia. The other three patients had established osteoporosis on the first DXA; they were initiated on bisphosphonate therapy alongside cinacalcet. Over the follow up period of between 2-7 years, BMD improved in all three patients. Discussion: Patients with established osteoporosis at the spine, TH and FN were started on appropriate anti-resorptive therapy and here, the role of cinacalcet on BMD was difficult to establish. Nevertheless, one lesson is that using forearm BMD as an additional marker of end-organ damage casts a wider net for diagnosing osteoporosis which is helpful to drive earlier use of bisphosphonates especially in conservatively managed PHPT. The decrease in PTH caused by cinacalcet is theoretically likely to have an impact on BMD. This case series shows stable osteopenia in two patients and a longer duration of 10 years (5 years with cinacalcet) for a third patient to advance to osteoporosis. Hence, cinacalcet could have a role in maintaining stable BMD especially at the early stages of PHPT when the patient has not yet progressed to osteoporosis. With cinacalcet proven to improve BMD in secondary hyperparathyroidism, more targeted studies in PHPT, with appropriate adjustment for confounding factors is required. Presentation: Monday, July 14, 2025