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Renal Osteodystrophy



- See:
         - Calcitriol
         - Hyperparathyroidism
         - Renal Failure: (Orders for the CRF Patient)
         - Renal Spondyloarthropathy
         - Vit D

- Effects on Adult Bone:
    - abnormalities of renal function can produce profound bone disease;
    - bone disease seen in renal failure is called renal osteodystrophy;
    - early stages of osteodystrophy:
          - effects on bone are primarily due to action of parathyroid hormone on osteocyte-osteoblast lining cell system, which is probably result of decreased phosphate excretion by the kidney;
          - w/ decreased phosphate excretion, there is elevation of plasma phosphate & complexing of calcium & phosphate in bone fluid;
          - as result, increasing amounts of PTH hormone are required to move the same amount of calcium from bone in order to maintain the plasma calcium at a constant level;
          - due to elevated parathyroid hormone levels, there is increase in number of bone remodeling centers & increase in bone turnover;
    - late stages:
          - when the glomerular filtration falls below 25% of normal, increased secretion of PTH is no longer able to maintain normal phospate levels, and the serum phosphate increases;
          - mineralization of previously osteomalacic bone then occurs, and osteosclerosis develops; (see ossification of soft tissue);
    - end stages:
          - diminished ability of kidney to hydroxylate vit D leads to a decrease in circulating levels of 1,25(OH)2D3 & produces decrease in intestinal calcium absorption;
          - calcification of osteoid is inhibited owing to deficiency of 1,25(OH)2D3, and owing to metabolic acidosis and other circulating inhibitors of mineralization that occur in uremic state;
    - net effect of renal dz on bone:
          - is combination of secondary hyperparathyroidism, osteomalacia, and osteosclerosis;
          - when bone disease becomes severe, pathologic fractures may occur, esp in ribs, pelvis, and hips;
          - uremic pts w/ advanced hyperparathyroidism appear prone to nontraumatic aseptic necrosis of the hips;
          - bone pain, frx, and concomitant muscle disease may be the major impediment to rehabilitation in chronic uremia;

- Effects in Children:
    - bone may appear diffusely sclerotic;
    - varus deformity of the proximal femurs may occur as a result of bone softening and osteomalacia;
    - growth plates are widened and zone of provisional calcification is poorly defined