Bone biopsy and clinical findings in patients with renal osteodystrophy

Renal osteodystrophy is a multifactorial disorder in patients with end-stage renal disease. The identification of secondary hyperparathyroidism and 1,25-dihydroxy-cholecalciferol (vitamin D-3) deficiency as major contributors to pathogenesis of renal osteodystrophy has led to the development of treatment regimens that can maintain normal serum calcium and phosphate concentrations, reduce parathyroid hormone secretion, and correct the vitamin D-3 deficiency. The most common type of renal osteodystrophy is osteitis fibrosa found in 50% of the patients affected (type IIIb, Delling ROD classification). However 30% of the patients present adynamic bone disease (type IIa, Delling ROD classification), with increased risk to fracture. Yet pathogenesis of the latter form remains poorly understood. To further characterize adynamic bone disease bone biopsies from 21 patients (13 females, 8 males, mean age 65 +/- 8 years, mean dialysis period 30 +/- 21 months) with histologically proven ROD type IIa were analyzed. The results of bone histomorphometry were compared to laboratory findings of the bone turnover (serum calcium, serum phosphate, alkaline phosphatase, parathormone, and vitamin D metabolites) and to bone mineral density of the forearm at the time of the biopsy. Furthermore histomorphometric results were compared to the histomorphometric results of a skeletal intact control group. We found no significant correlation between laboratory findings and histomorphometric data, especially to parathormone and alkaline phosphatase. However in 80% of the cases there was a high correlation between trabecular bone volume of the biopsy and bone mineral density of the forearm. Patients with adynamic bone disease present a decreased number of osteoclasts and osteoblasts as compared to healthy controls, also eroded surface was decreased. In contrast there was an increased osteoid surface, while the osteoid volume and the osteoid thickness remained unchanged. We therefore conclude that laboratory findings and bone mineral density are helpful methods in differentiation of bone turnover and bone mineral content, but bone biopsy is needed and remains the hallmark in diagnosis of the correct type of renal osteodystrophy.