[Renal osteodystrophy (3); its treatment in dialysis patients]

The prevalence and the clinical gravity of the various histopathological varieties of renal osteodystrophy in dialysis patients depends on the severity of both the aluminium intoxication and that of hyperparathyroidism. The prevalence of bone pains, fractures and hypercalcemias are the highest in adynamic bone diseases (ABD) with severe aluminium intoxication, then in osteitis fibrosa and mixed osteopathy, in the ABD with moderate aluminium intoxication and rare in the mild lesion in spite of similar moderate aluminium intoxication. In the absence of aluminium intoxication, hypercalcemia and hyperphosphatemia prevalence is higher only when intact PTH is more that 4 times the upper limit of normal. When PTH is between 1 and 2 folds the ULN this prevalence is null and bone mineral density is the highest. 2. The low turnover aluminic bone diseases (osteomalacic or adynamic) will be cured by long term deferoxamine treatment. The hazards of such treatment justify the performance of a bone biopsy to ensure the diagnosis. Their prevention relies on adequate treatment of tapwater and definitive exclusion of long term administration of aluminum phosphate binders. 3. Non aluminic osteomalacia will be treated according to the same guidelines given for the uremic patients before dialysis. 4. Non aluminic adynamic bone disease will be cured by means aiming at stimulating PTH secretion as discontinuing 1 alpha hydroxylated vitamin D derivatives, and, if there is no hyperphosphatemia by discontinuation of calcium supplement. In case of hyperphosphatemia in dialysis patients CaCO3 doses have to be nevertheless increased after the dialysate calcium concentration (DCa) has been decreased in order to induce a negative perdialytic calcium balance for PTH secretion stimulation. In the near future substitution of CaCO3 by non calcemic non aluminic phosphate binders will suffice. 5. Osteitis fibrosa due to hyperparathyroidism will be treated first by securing an optimal vitamin D repletion (bringing plasma 25OH vitamin D around 30 and 60 ng/ml or 75-150 nmol/l) and by correcting hypocalcemia and hyperphosphatemia by CaCO3 at high doses (3-12 g/day) taken with the meals. In case of hypercalcemia dialysate calcium concentration will be decreased to correct it or, in a near future, CaCO3 will be decreased to 3 g/day and hyperphosphatemia will be controlled by non calcemic, non aluminic phosphate binders. When hyperphosphatemia is controlled whereas plasma calcium is normal or low, 1 alpha hydroxylated vitamin D derivatives can be administered. 6. Instrumental parathyroidectomy should be considered when plasma levels of intact PTH remain above 7 folds the upper limit of normal whereas hyperphosphatemia persists and hypercalcemia occurs in order to prevent thining of the corticals and subsequent fracture risk. In case of previous exposition to aluminum, a deferoxamine test and/or a bone biopsy will be performed to decide a long term DFO treatment before the parathyroidectomy in order to prevent the transformation of a mixed osteopathy into an aluminic adynamic bone disease. 7. The difficulty of hyperparathyroidism control in dialysis patients is due to poor compliance to phosphate binders and to irreversible parathyroid hyperplasia with occured before the dialysis stage. This stress the primary importance if its early prevention without iatrogenia by first CaCO3 and vitamin D repletion, as soon as the creatinine clearance decreases below 60 ml/min/1.73 m2.