Vitamin D deficiency influences histomorphometric features of bone in primary hyperparathyroidism

Introduction: Vitamin D deficiency is common in patients with primary hyperparathyroidism (PHPT). The presence of low levels of vitamin D may affect the skeletal consequences of PHPT.

Methods: In this cross-sectional study, transiliac crest bone biopsies were performed after double tetracycline labeling in patients with mild PHPT and analyzed according to serum levels of 25 hydroxyvitamin D (25OHD).

Results: We studied 30 patients with mild PHPT (age 53 ± 11 years; 67% women; calcium 11.1 ± 1.0 mg/dl; PTH 149 ± 129 pg/ml). Serum 25OHD levels were low in the majority of subjects (mean 21 ± 11 ng/ml) and inversely associated with PTH (r = -0.69; p < 0.01). 25OHD levels were directly associated with cortical width (Ct.Wi; r = 0.46, p < 0.03) and trabecular separation (Tb.Sp; r = 0.41; p < 0.04), but inversely associated with cancellous bone volume (BV/TV; r = -0.39, p < 0.04). Subjects with 25OHD levels < 20 ng/ml (n = 14) and ≥ 20 ng/ml (n = 16) were compared. Groups did not differ by age, sex, menopausal status, serum calcium, creatinine, or 1,25(OH)₂D. PTH was 1.8-fold higher in subjects with 25OHD < 20 (265 ± 166 pg/ml vs. 95 ± 50 pg/ml; p < 0.01). On histomorphometric analysis, those with low 25OHD had lower Ct.Wi (541 ± 167 μm vs. 712 ± 200 μm; p < 0.03). Conversely, measures of trabecular microarchitecture were better in those with lower 25OHD, with higher BV/TV (26.1 ± 6.1% vs. 20.4 ± 6.4%; p < 0.03), greater trabecular number (Tb.N: 2.0 ± 0.4 mm⁻¹ vs. 1.8 ± 0.4 mm⁻¹; p < 0.04) and lower Tb.Sp (371 ± 90 μm vs. 472 ± 137 μm; p < 0.04). There were no differences between the groups in bone remodeling indices.

Conclusions: Low levels of 25OHD in patients with PHPT are associated with higher concentrations of PTH, greater catabolic effects in cortical bone and greater anabolic effects in trabecular bone.