Bone changes in hypercalcemia of malignancy in dogs.

Bone was collected for trabecular bone morphometry from 6 dogs with hypercalcemia of malignancy. Five of the dogs had lymphosarcoma and 1 had an anal sac apocrine gland carcinoma with vertebral metastases. Parathyroid gland weights varied around normal, with those for 1 dog being slightly low and those for another dog being moderately increased. As a group, the dogs had decreased bone volume, with increased resorption surfaces and increased numbers of osteoclasts. In 4 dogs, osteoid seams and osteoblasts were limited in extent and this distinguished them from dogs with hyperparathyroidism. Although most dogs had received corticosteroids, chemotherapy, or radiation treatment, the bone changes in these dogs were similar to 1 dog that had not received treatment. Also, the changes could not be related to uremia or renal mineralization that had developed in 2 of the dogs. Two of the dogs had somewhat greater amounts of osteoid-covered surface and slightly widened osteoid seams, ie, findings more like those of hyperparathyroidism. One of these dogs had anal sac apocrine gland carcinoma and the other had lymphosarcoma in which there was invasion of the bone cortex at the sampling site. It was concluded that bone remodeling changes do occur in hypercalcemia of malignancy and that these changes are varied and often are not those of hyperparathyroidism.