Conjunctival and corneal calcification and bone metabolism in hemodialysis patients

Conjunctival and corneal calcification is well recognized as a metastatic calcification in patients undergoing hemodialysis. In 44 male hemodialysis patients, we examined the relationship between the severity of conjunctival and corneal calcification and age; duration of hemodialysis; serum levels of calcium (Ca), phosphorus (P), intact parathyroid hormone (iPTH), alkaline phosphatase (ALP), and osteocalcin; and bone mineral density (BMD). The mean age was 58.3 years (range, 33-79 yr), and the mean duration of hemodialysis was 94.3 months (range, 25-258 mo). The serum level of Ca was 9.6 +/- 0.1 mg/dL, P was 5.9 +/- 0.1 mg/dL, Ca x P was 57.5 +/- 1.2, iPTH was 204.0 +/- 34.6 pg/mL, ALP was 173.8 +/- 11.8 U/L, and osteocalcin was 62.8 +/- 9.5 ng/mL. Lumbar BMD was 0.997 +/- 0.022 g/cm2 and radial BMD was 0.642 +/- 0.015 g/cm2. There was a significant positive correlation between the severity of conjunctival and corneal calcification and the duration of hemodialysis (P < 0.0001), the serum levels of P (P = 0.0035), the Ca x P (P = 0.0034), the iPTH (P = 0.0154), the ALP (P < 0.0001), and the osteocalcin (P = 0.0010), and was negatively correlated with radial BMD (P = 0.0008). However, the severity of conjunctival and corneal calcification was not significantly correlated with age (P = 0.986), serum Ca levels (P = 0.138), or lumbar BMD (P = 0.449). Based on these findings, we suggest that the conjunctival and corneal calcification developed by excessive serum levels of Ca and P associated with abnormal bone and mineral metabolism. This resulted in an increased bone turnover and decreased BDM after prolonged hemodialysis even though efforts were made to maintain the homeostasis of Ca and P metabolism in hemodialysis patients by using various therapeutic approaches.