Hypercalcemia Health Article

Description

Hypercalcemia is an abnormally high level of calcium in the blood, usually more than 10.5 milligrams per deciliter of blood. It is the most common life-threatening metabolic disorder associated with cancer.

Calcium plays an important role in the development and maintenance of bones in the body. It is also needed in tooth formation and is important in other body functions. As much as 99% of the body's calcium is stored in bone tissue. A healthy person experiences a constant turnover of calcium as bone tissue is built and reshaped. The remaining 1% of the body's calcium circulates in the blood and other body fluids. Calcium in the blood plays an important role in the control of many body functions, including blood clotting, transmission of nerve impulses, muscle contraction, and other metabolic activities.

Cancer-caused hypercalcemia produces a disruption in the body's ability to maintain a normal level of calcium. This abnormally high level of calcium in the blood develops because of increased bone breakdown and release of calcium from the bone. The disorder occurs in approximately 10-20% of all cancer cases. The most common cancers associated with hypercalcemia are breast, prostate, and lung cancer, as well as multiple myeloma or other tumors with extensive metastasis to the bone. It may also occur in patients with head and neck cancer, cancer of unknown primary, lymphoma, leukemia, kidney cancer, and gastrointestinal cancer. Hypercalcemia most commonly develops as a late complication of cancer, and its appearance constitutes an emergency.

Several clinical symptoms are associated with cancer-related hypercalcemia. Symptoms may appear gradually and often look like signs of other cancers and diseases. The symptoms of hypercalcemia are not only related to the elevated level of calcium in the blood, but—more importantly—to how rapidly the hypercalcemia develops. The severity of the symptoms is often dependent upon factors such as previous cancer treatment, reactions to medications, or other illnesses a patient may have. Most patients do not experience all of the symptoms of hypercalcemia, and some may not have any signs at all. Rapid diagnosis of hypercalcemia may be complicated because the symptoms are often nonspecific and are easily ascribed to other factors. These symptoms include:

• decreased muscle tone and muscle weakness
• delirium, disorientation, incoherent speech, and psychotic symptoms such as hallucinations and delusion
• constipation
• fatigue
• poor appetite, nausea and/or vomiting
• frequency of urination and increased thirst
• pain

Causes

The fundamental cause of cancer-related hypercalcemia is increased movement of calcium out of the bones and into the bloodstream, and secondarily, an inadequate ability of the kidneys to get rid of higher calcium levels. Normally, healthy kidneys are able to filter out large amounts of calcium from the blood, getting rid of the excess that is unneeded by the body and keeping the amount of the calcium the body does need. However, the high levels of calcium in the body caused by cancer-related hypercalcemia may cause the kidneys to become overworked, thus making them unable to excrete the excess. Another problem is that some tumors produce a substance that may cause the kidneys to get rid of too little calcium.

Two types of cancer-caused hypercalcemia have been identified: osteolytic and humoral. Osteolytic occurs because of direct bone destruction by a primary or metastatic tumor. Humoral is caused by certain factors secreted by malignant cells, which ultimately cause calcium loss from the bones. Certain types of hormonal therapy may precipitate hypercalcemia and the use of some diuretics may contribute to the disorder.

Because immobility causes an increase in the loss of calcium from bone, cancer patients who are weak and spend most of their time in bed are more prone to hypercalcemia. Cancer patients are often dehydrated because they take in inadequate amounts of food and fluids and often suffer from nausea and vomiting. Dehydration reduces the ability of the kidneys to remove excess calcium from the body, and therefore is another contributing factor in the development of hypercalcemia in cancer patients.