Chronic kidney disease and the skeleton

Fractures across the stages of chronic kidney disease (CKD) could be due to osteoporosis, some form of renal osteodystrophy defined by specific quantitative histomorphometry or chronic kidney disease–mineral and bone disorder (CKD–MBD). CKD–MBD is a systemic disease that links disorders of mineral and bone metabolism due to CKD to either one or all of the following: abnormalities of calcium, phosphorus, parathyroid hormone or vitamin D metabolism; abnormalities in bone turnover, mineralization, volume, linear growth or strength; or vascular or other soft-tissue calcification. Osteoporosis, as defined by the National Institutes of Health, may coexist with renal osteodystrophy or CKD–MBD. Differentiation among these disorders is required to manage correctly the correct disorder to reduce the risk of fractures. While the World Health Organization (WHO) bone mineral density (BMD) criteria for osteoporosis can be used in patients with stages 1–3 CKD, the disorders of bone turnover become so aberrant by stages 4 and 5 CKD that neither the WHO criteria nor the occurrence of a fragility fracture can be used for the diagnosis of osteoporosis. The diagnosis of osteoporosis in stages 4 and 5 CKD is one of the exclusion—excluding either renal osteodystrophy or CKD–MBD as the cause of low BMD or fragility fractures. Differentiations among the disorders of renal osteodystrophy, CKD–MBD or osteoporosis are dependent on the measurement of specific biochemical markers, including serum parathyroid hormone (PTH) and/or quantitative bone histomorphometry. Management of fractures in stages 1–3 CKD does not differ in persons with or without CKD with osteoporosis assuming that there is no evidence for CKD–MBD, clinically suspected by elevated PTH, hyperphosphatemia or fibroblast growth factor 23 due to CKD. Treatment of fractures in persons with osteoporosis and stages 4 and 5 CKD is not evidence-based, with the exception of post-hoc analysis suggesting efficacy and safety of specific osteoporosis therapies (alendronate, risedronate and denosumab) in stage 4 CKD. This review also discusses how to diagnose and manage fragility fractures across the five stages of CKD. Distinguishing between fractures related to kidney disease or osteoporosis is clinically challenging but important for treatment. Paul Miller from the Colorado Center for Bone Research in Lakewood, USA, reviewed the intimate biological relationships between the kidney and skeleton that can result in bone diseases that increase the risk of low-trauma fracture. Diagnosing whether fractures are related to chronic kidney disease (CKD) or osteoporosis is important as patients are managed differently. Diagnosis can be difficult because both diseases are characterized by low bone mineral density and low-trauma fractures. Analyzing bone structure and biomarkers of bone turnover should exclude osteoporosis in patients with severe CKD and low-trauma fractures. Although more information is needed on the use of approved osteoporosis drugs in CKD-related bone disease, drugs in development may offer more targeted therapy.