HYPERPARATHYROIDISM SECONDARY TO RENAL-IN SUFFICIENCY - PATHOPHYSIOLOGY, CLINICORADIOLOGICAL ASPECTS AND TREATMENT

Stimulation of PTH secretion and synthesis in chronic renal failure in volves direct and indirect factors. The indirect ones are those contri buting to a decrease of plasma ionized calcium concentration which sti mulates the release of PTH (I) primarily the negative calcium balance due to the iatrogenic reduction of dietary calcium intake associated w ith an inadequate synthesis of calcitriol, this latter being explained by a reduction in the nephronic mass, the phosphate retention, the ac idosis and the retention of uremic toxins (2) more accessorily, the ph ysicochemical dysequilibrium induced by the late occuring hyperphospha temia. The factors acting directly on the parathyroid gland stimulatin g synthesis of prepro PTH at its transcription level: not only hypocal citriolemia but also hypocalcemia and hyperphosphatemia. The clinicora diological manifestations appear late, mostly only after the patient h as been put on dialysis. The most precocious sign is the subperiosteal resorption assessed on the hand Xrays. Therefore diagnosis of hyperpa rathyroidism relies mainly on the measurement of plasma concentration of intact PTH. In dialysis patients the optimal range corresponding to the best bone histology is between 1 an 3 times the upper limit of no rmal. No such data exist for predialysis patients. Medical treatment o f hyperparathyroidism should primarily be preventive, probably in pred ialysis lipin patient as soon as plasma intact PTH is greater than the normal upper limit. This treatment is based primarily on the preventi on of phosphate retention, of negative calcium balance and acidosis by the use of oral alkaline salts of calcium given with the meals in ass ociation with appropriate dietary protein and phosphate restriction. N ative vitamin D depletion should also be prevented but use of 1 alpha OH vitamin D3 metabolites in controversial : it is reasonable to admin ister them only when plasma intent PTH is above 3-7 the normal upper l imit and when plasma phosphate is below 1.2 in predialysis patients be low 1.5 mmol/l in dialysis patients and plasma calcium remains below 2 .3 mmol/l in spite of CaCO3 administration. This situation is encounte red in less than 50% of the dialysis patients and rarely in predialysi s patients. In dialysis patients the calcium concentration in the dial ysate should be chosen in relation to the dose of oral calcium and the use of 1 alpha OH vitamin D3. The superiority of the intermittent (or al or intravenous) over the daily oral administration is not yet clini cally proven. The surgical parathyroidectomy is indicated when hyperca lcemia and/or hyperphosphatemia occur under medical treatment, whereas the intact PTH levels remain very high (> 500 pg/ml). Necrotic ulcera tions of the extremities in relation to calciphylaxis is an urgent PTX indication. At the latter exception, PTX should be performed only aft er exclusion or treatment of aluminium overload by deforoxamine.