[Half of the patients with primary hyperparathyroidisms have a vitamin D deficiency: aggravating the osseous attack].

Background: Primary hyperparathyroidism (PHPT) associates hypocalcemia and hypophosphatemia secondary to parathyroid hormone (PTH) excess. PHPT is asymptomatic for 80% of patients and responsible for a decrease in bone mineral density particularly in women. Vitamin D deficiency increases the risk of bone fractures.

Methods: We performed a prospective analysis of patients with PHPT in order to evaluate the prevalence of vitamin D deficiency. We determined the effects of vitamin D deficiency on bone metabolism: calcium, phosphate and PTH levels. We also analyzed biochemical markers of bone remodeling and bone mineral density (BMD) before and 6 months after vitamin D replacement.

Results: 75 patients with PHPT were identified: 38 patients with vitamin D deficiency but only 22 patients could be followed (G1). 14 patients with a normal level of vitamin D were followed (G2). Prevalence of vitamin D deficiency was 51%. Calcium and phosphate levels were similar into both groups. PTH levels were higher in the G1 group. Calciuria was significantly lower in the G1. For markers of bone formation (fragments of collagen CTX and alkaline phosphatase): osteocalcine levels were higher in G1 group. For bone resorption: télopeptides levels were significantly higher in the G1 group. T score was significantly lower in this group, favoring a significant osseous attack. After 6 months of substitution with vitamin D, calcium decreased and hypophosphatemia normalized. PTH levels decreased (-50.7%). Calciuria increased without risks of urinary lithiasis. Bone mineral density loss decreased while markers of bone turn over increased.

Discussion: Vitamin D deficiency increases the risk of bone fragility in PHPT. Few data are available in France concerning the prevalence of vitamin D deficiency in PHPT. Our results were similar to data in other countries. Vitamin D replacement with regular monitoring of calcium and calciuria levels is beneficial for metabolic and hormonal status, improves bone density, without systematic opposing effects. The follow-up of effectiveness by BMD could be associated with measurement of markers of bone remodeling.

Conclusion: In asymptomatic PHPT, particularly those for which surgery is not indicated, measurement of 25 OH Vitamin D should be systematic. It is recommended before surgery.