Mild primary hyperparathyroidism (PHPT) is characterized by asymptomatic hypercalcemia, most commonly in the absence of classical signs and symptoms. Hence, there is need to characterize this disorder with particular attention to the skeleton.

We determined the ratio of pyr and deH-DHLNL collagen cross-links in 46 iliac crest bone biopsies from patients with PHPT (14 men, aged 28–68; 32 women, aged 26–74) by Fourier transform infrared imaging (FTIRI). The results were compared with previously reported collagen cross-links ratio determined in iliac crest biopsies from normal subjects.

PHPT patients exhibited significantly lower pyr / deH-DHLNL collagen cross-links ratio compared to normal controls. Parathyroidectomy restored values to those comparable to normal controls. Moreover, the differences among PHPT subjects were gender-dependent with female PHPT patients having a statistically significant lower ratio compared to either male PHPT patients or normal controls. Comparison of the obtained outcomes with histomorphometry showed that the collagen cross-link ratio was strongly correlated with rate of bone formation, and mineralizing surface, in individual patients. This ratio was also correlated with bone mineralization density distribution (BMDD) parameters obtained in the same patients. The strongest correlations were with BMDD variables reflecting heterogeneity of mineralization and primary mineralization parameters.

The results are consistent with the high turnover state manifested in PHPT patients. Reduced collagen cross-link ratio in patients with PHPT would be expected to reduce the stiffness of bone tissue. These observations provide a more complete assessment of bone material properties in this disorder.