Bone changes in hemodialyzed uremic subjects. Comparative light and electron microscope investigations

Needle biopsies from the iliac crest of 40 uremic patients treated with hemodialysis have been compared by light and electron microscopy. The most obvious bone changes were represented by an increased amount of osteoid tissue (osteomalacic changes) and by enhanced bone resorption. The osteomalacic changes were chiefly characterized by the presence of thick osteoid borders whose collagen fibrils were often completely uncalcified. In a few cases, small roundish aggregates of crystals were irregularly present through the osteoid matrix; some of them were closely related to roundish, electron-dense bodies surrounded by a membrane. The increased rate of bone resorption, which was often comparable to that which occurs in the most severe cases of primary hyperparathyroidism, was due to both osteoclastic activity and osteocytic osteolysis. Electron microscopy showed that the enlargement and irregularity of the osteocytic lacunae were not always due to osteocytic osteolysis; the same effect might be due to defective calcification of the lacunar wall. The advantages of comparing the same specimens under the light and electron microscopes are discussed.