FGF23 and primary hyperparathyroidism: is there a link?

INTRODUCTION: Data regarding the role of fibroblast growth factor 23 (FGF23) in primary hyperparathyroidism (PHPT) are scarce and discordant. Our study aimed to evaluate the prognostic impact of FGF23 upon the clinical and biochemical evolution of PHPT. MATERIAL AND METHODS: Forty-two patients with ages between 30 and 80 years, diagnosed with PHPT caused by a sporadic, solitary parathyroid adenoma, and referred to surgery (minimally invasive parathyroidectomy) were prospectively included in the study. Serum levels of FGF23, PTH, 25(OH)D3, calcium (Ca), phosphate (P), total procollagen type 1 N-terminal propeptide, and C-terminal telopeptide of type I collagen were determined at baseline (preoperatory), one day after surgery, and in 13 patients also prospectively at three, six, and 12 months. Bone mineral density (BMD) was also evaluated before surgery in all patients and 12 months after surgery in the 13 followed up patients. RESULTS: In the 42 PHPT patients with D hypovitaminosis (mean 25(OH)D3 levels of 16.2 ± 1.5 ng/mL), preoperatory serum FGF23 concentration was within the normal range (75.55 ± 3.39 pg/mL) and remained unchanged one day post operation (81.69 ± 4.67 pg/mL, p = non-significant). The 13 patients followed prospectively for up to 12 months after surgery also showed unmodified FGF23 levels (80.9 ± 11.03 pg/mL, p = non-significant), despite PTH and Ca normalisation and vitamin D replenishment. Preoperatory FGF23 negatively correlated with PTH (r = -0.37, p = 0.038), but not with 25(OH)D3, Ca, P, bone mass, or metabolism markers. CONCLUSIONS: In PHPT, correlations between FGF23 and PTH seem rather an epiphenomenon. Therefore, we think that FGF23 evaluation and dynamics are not informative regarding PHPT severity. (Endokrynol Pol 2020; 71 (4): 306-312).

ATYPICAL PRIMARY HYPERPARATHYROIDISM DUE TO HYPOVITAMINOSIS D.

Vitamin D deficiency is nowadays very common in the general population and also in patients with primary hyperparathyroidism. Hypovitaminosis D may modify the clinical features and the severity of primary hyperparathyroidism. We present the case of a 75-year-old woman with a 10 year history of nephrolithiasis and severe osteoporosis, with multiple fragility fractures. Her bone and kidney status required a more thorough metabolic assessment. Despite minimal changes in serum calcium and phosphate levels, parathyroid hormone (PTH) level was markedly elevated. Ultrasound and specific Sesta-MIBI scintigraphy diagnosed and localized a left parathyroid adenoma. Vitamin D assessment showed levels in the range of hypovitaminosis. Vitamin D deficiency may mask hypercalcemia despite high serum PTH levels, and does not seem to diminish but on the contrary increases the risk of kidney lithiasis, as well as the deleterious effects of hyperparathyroidism on bone.