My dog was diagnosed as having hypercalcemia. His veterinarian has scheduled some additional tests and x-rays. The doctor said a surgical biopsy might be necessary as well. Is this a disease? What causes it and how is it treated?
Hypercalcemia, or abnormal elevation of calcium in the blood, may result from a number of underlying disorders. Calcium levels can easily rise to toxic levels, at which point clinical signs develop as calcium-caused primary ailments begin. Treatment is aimed at the underlying disorder, but if calcium toxicity is severe, steps will need to be taken to directly reduce the calcium levels also. Hypercalcemia does not occur often in dogs. Its presence in cats is rare.
The high-normal serum calcium level in dogs is about 12 mg/dl and in cats is about 11 mg/dl. Signs of hypercalcemia usually begin after the level has exceeded 14 mg/dl. When calcium builds up in the blood, it affects the kidneys, the intestines and the nervous system. As a result, the affected animal will have signs, which may include excessive thirst and urination, loss of appetite, constipation, vomiting, lethargy and weakness. Seizures are also possible, although in most cases veterinary attention is sought before the disorder has progressed to that point. Abnormalities may also be seen on the electrocardiograms of hypercalcemic animals.
The two most common underlying disorders that produce hypercalcemia are certain cancers and primary hyperparathyroidism. Cancerous tumors, including lymphosarcoma, bone and anal sac tumors produce substances that stimulate the release of calcium from bone. These substances mimic the effect of parathyroid hormone (PTH), a process called pseudohyperparathyroidism. Direct destruction of bone by bone tumors also breaks down bone calcium stores, releasing calcium into the blood stream. Cancer is the most common underlying cause of hypercalcemia in dogs and cats.
Primary hyperparathyroidism is the second most common cause, which is usually related to the presence of a solitary benign tumor of the parathyroid gland. Diffuse glandular hyperplasia and malignant tumors of the parathyroid gland are less common causes of hyperparathyroidism and hypercalcemia. These disorders cause excessive amounts of PTH to be produced and excreted. The excessive PTH stimulates the removal of calcium from bone and an increase of calcium absorption from the intestines, leading to hypercalcemia.
Other causes of hypercalcemia include excessive intake of vitamin D, hypoadrenocorticism (Addison's disease), bone disease, certain types of renal failure and granulomatous infections. Excessive vitamin D intake (hypervitaminosis D) arises from over-supplementation of vitamin D, or when an animal kills or eats rodents that have ingested a vitamin D-based rodent poison. Addison's disease (underactive adrenal gland; hypoadrenocorticism) causes dehydration and decreased kidney excretion of calcium; this results in the hemoconcentration of calcium. Kidney disease and other disorders may stimulate the parathyroid gland to produce excess PTH as well (secondary hyperparathyroidism). Infectious granulomatous diseases, like tuberculosis, can cause hypercalcemia, albeit rarely.
Diagnosis of the problem underlying the hypercalcemia involves bloodwork and possibly radiographs, ultrasonography, and tissue biopsy to look for evidence of cancer. Parathyroid hormone levels in the blood are compared to levels of ionized blood calcium; this test is most often submitted to reference laboratories, which may result in a delayed report. If the levels of PTH are normal or high when the blood calcium is elevated, then this is an inappropriate balance that suggests a diagnosis of primary hyperparathyroidism. Ultrasound of the neck has become a reliable tool for verifying mass lesions or enlargement of the parathyroid glands when performed by an experienced technician.
Treatment of the underlying disorder will follow definitive diagnosis. In severe cases, hypercalcemia can cause cardiac abnormalities, seizures, and acute kidney failure. To prevent these problems the hypercalcemia will also be directly treated if necessary. Several therapeutic measures may be undertaken to reduce serum calcium levels. Intravenous infusion of saline solutions (physiologic salt water) will expand the volume of fluid in the circulation. This reduces the blood's calcium concentration (by dilution) and promotes urinary excretion of it as well. Certain diuretics may be used for this purpose also. Administration of glucocorticosteroids will reduce bone release of calcium. Additionally, these medications will decrease intestinal absorption of calcium and increase calcium excretion by the kidneys. Calcitonin, a hormone that decreases the loss of calcium from bone, and certain other medications may be helpful.
The prognosis for recovery depends on the underlying cause of the hypercalcemia and how damaging the high calcium levels were to the kidneys, heart, and other organs. Lymphosarcoma and other cancers carry a guarded to poor prognosis, while primary hyperparathyroidism is frequently cured with surgery or newer treatments.
12/15/00
