Endocrine Abstracts

Introduction: The role of vitamin D and calcium metabolism has long been implicated in the clinical manifestation of primary hyperparathyroidism (PHPT). The skeletal response to the overproduction of PTH is less predictable, and the effect on bone loss can be greater in some patients. In this study, we established associations between vitamin D metabolism, vitamin D metabolite ratio (VMR) 1,25OH2D:24,25OH2D with rates of bone loss in PHPT patients who did not undergo surgery.

Methods: An audit was conducted from the electronic health records of PHPT patients from the Endocrinology clinic at the NNUH during 2017-2019. The search identified patient cases n=13(age mean (range): female (n=9)70.6(50-94)yrs, male n=473(63-79)yrs, VMR ≥51), with age/gender matched controls (VMR <51) Excluded were those who had parathyroid surgery. Serum 25OHD, adjusted calcium, phosphate and PTH were retrieved with bone mineral density (BMD) T-score values (lumbar, left hip and left femoral neck) from DEXA scans carried out ±1 month of biochemical measurements.

Results: We observed a significantly lower Lumbar Spine T-score in the cases, mean(95%CI) -1.85(-0.9 to -2.77) than in the controls -0.2(0.30 to -0.79), P<0.001. Whilst the left hip and left femoral neck T-scores in the cases were lower but not statistically significant. 25OHD and 24,25OH2D were significantly lower in the cases than controls; mean(SEM) 42.9(6.6)/69.4(3.9) nmol/l, P<0.01 and 2.0(0.44)/5.0(0.38) nmol/l, P<0.001, respectively. In contrast, the 25OHD:24,25OH2D VMR in the cases were higher 27(2.0)/15(0.8), P<0.001.

Conclusion: Our cohort of non-surgically managed PHPT patients presented with elevated 1,25OH2D:24,25OH2D VMR were strongly associated with lower Lumbar Spine T-score. By using VMR we demonstrated an imbalance between the active and catabolic forms of vitamin D metabolites, that may play a role in altering the responsiveness to PTH and accelerating bone loss.