Cancer is the uncontrolled growth of cells that are able to invade neighboring tissues. The cells divide over and over, forming a tumor. Cancers can develop anywhere in your body, and many of them can metastasize, or spread. They can be rapid- or slow-growing, and can disrupt the function of the tissues they are invading. In addition, they may cause other changes to your body, including to your body chemistry. Lung cancers in particular can lower the sodium levels in your blood.
Cancer Syndromes
Tissue destruction is one cause of disease for those with cancer. In addition, the cancer and your body's reaction to it can produce chemicals that change your physiology. The disease or symptom, which is caused by the presence of the cancer, but not by the local invasion of tumor cells, is called a "paraneoplastic syndrome."
Lung cancer can be classified as small cell and non-small cell lung cancer. Small cell lung cancer can cause a paraneoplastic syndrome of low sodium in the blood. It does this by secreting antidiuretic hormone, often referred to as ADH. The condition is called SIADH, which stands for "syndrome of inappropriate antidiuretic hormone."
Antidiuretic Hormone
Antidiuretic hormone is a protein hormone released by the pituitary gland, located under your brain. It signals the kidneys to retain water and increases blood pressure. Small cell lung cancer can secrete ADH as well. As a result your kidneys take up water. This dilutes the blood, and makes sodium levels less concentrated. The low sodium level is caused by excessive water from high levels of ADH secreted by the tumor.
Effects
Mildly to moderately low sodium levels may produce no symptoms. Very low sodium can produce nerve dysfunction, changes in consciousness, irritability, fatigue, nausea, coma and even death. Muscle problems can include spasms and cramps. Other symptoms may include vomiting, headache and seizures.
Diagnosis and Treatment
The diagnosis of low blood sodium in the context of known lung cancer raises the suspicion for SIADH. Further studies of your urine and blood can establish the presence of excessive ADH. Treatment involves fighting the tumor, increasing the sodium slowly and carefully with saline, restricting pure water intake, and starting the administration of drugs such as demeclocycline. You should consult with a physician for the diagnosis and treatment of disease.
References
- "Harrison's Principles of Internal Medicine"; Anthony S Fauci, et al.; 17th Ed 2008
- "Robbins and Cotran Pathologic Basis of Disease"; Vinay Kumar, et al.; 8th Ed 2009
