[Histomorphometric data in 5 cases of pseudohypoparathyroidism: discussion on bone sensitivity to parathyroid hormone].

We studied 5 patients (aged 8 to 18) presenting chronic calcipenia with hyperphosphatemia and an increase in C terminal-specific immunoreactive parathyroid hormone. Systematic radiography of the hands revealed 2 cases with signs of subperiosteal resorption characteristic of hyperparathyroidism and 2 cases of cortical fibrillation. These cases were monitored by measuring phosphate levels in the urine after injection of parathyroid hormone (Ellsworth-Howard test), by determining urinary elimination of cyclic AMP after injection of parathyroid hormone (Chase-Aurbach test) and by assaying cyclic AMP levels in the plasma after intravenous administration of parathyroid hormone (Tomlinson-Hendy test). These 3 measurements revealed no changes upon injection of parathyroid hormone, even after administration of vitamin D, thus suggesting renal resistance to parathyroid hormone. The absence of cyclic AMP secretion is suggestive of perturbation of the membrane receptor. Histomorphometric study of the bones showed an increase in resorption and osteoid areas and in the relative osteoid volume without modification of osteoid thickness, which is very suggestive of an effect of parathyroid hormone on the bone. Pseudohypoparathyroidism was, then, characterized by renal resistance to parathyroid hormone and an effect of the latter on bone cells.