Spectrum of bone pathologies in chronic kidney disease

Histologic bone abnormalities begin very early in the course of chronic kidney disease. The KDIGO guidelines recommend that bone disease in patients with chronic kidney disease should be diagnosed on the basis of bone biopsy examination, with bone histomorphometry. They have also proposed a new classification system (TMV), using three key features of bone histology—turnover, mineralization, and volume—to describe bone disease in these patients. However, bone biopsy is still rarely performed today, as it involves an invasive procedure and highly specialized laboratory techniques. High-turnover bone disease (osteitis fibrosa cystica) is mainly related to secondary hyperparathyroidism and is characterized by increased rates of both bone formation and resorption, with extensive osteoclast and osteoblast activity, and a progressive increase in peritrabecular marrow space fibrosis. On the other hand, low-turnover (adynamic) bone disease involves a decline in osteoblast and osteoclast activities, reduced new bone formation and mineralization, and endosteal fibrosis. The pathophysiological mechanisms of adynamic bone include vitamin D deficiency, hyperphosphataemia, metabolic acidosis, inflammation, low oestrogen and testosterone levels, bone resistance to parathyroid hormone, and high serum fibroblast growth factor 23. Mixed uraemic osteodystrophy describes a combination of osteitis fibrosa and mineralization defect. In the past few decades, an increase in the prevalence of mixed uraemic osteodystrophy and adynamic bone disease has been observed.