Osteoporosis and Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD): Back to Basics.

Osteoporosis is defined as "a skeletal disorder of compromised bone strength predisposing to an increased risk of fracture". However, based on bone histology, the term osteoporosis is only part of a spectrum of skeletal complications that includes osteomalacia and the various forms of renal osteodystrophy of chronic kidney disease-mineral and bone disorder (CKD-MBD). In addition, a label, "kidney-induced osteoporosis", has been proposed, despite the fact that CKD does not cause osteoporosis, as is diagnosed histologically. It is clear, therefore, that such terminology may not be helpful diagnostically or in making treatment decisions. A new label, CKD-MBD/Osteoporosis could be a more appropriate term as it brings osteoporosis under the official label of CKD-MBD.. Neither laboratory nor non-invasive diagnostic investigations can discriminate osteoporosis from the several forms of renal osteodystrophy. Transiliac crest bone biopsy can make the diagnosis of osteoporosis by exclusion of other kidney-associated bone diseases but its availability is limited. Recently, classification of metabolic bone diseases based on bone turnover, from low to high, together with mineralization, and bone volume, has been proposed. Therapeutically, no antifracture treatments have been FDA approved for patients with kidney-associated bone disease. Agents that suppress PTH (vitamin D analogues and calcimimetics) are used to treat hyperparathyroid bone disease. Antiresorptive and osteoanabolic agents approved for osteoporosis are being used off label in stage 3B-5 CKD in high risk patients. It has now been suggested that intermittent administration of PTH, as early as stage 2 CKD, could be an effective management. If confirmed in clinical trials, it could mitigate the retention of phosphorus and subsequently the rise in FGF-23 and, it may be beneficial for co-existing osteoporosis.