Sodium is one of the major electrolytes, carefully maintained within a narrow normal range and necessary for proper functioning of your body's systems. Low sodium levels, or hyponatremia, occur in a wide variety of medical disorders including cancer. You need to recognize that the symptoms of hyponatremia, appropriate blood testing and timely treatment all play a role in the approach to sodium imbalance.
The mineral sodium, along with chloride and potassium, serves as a key electrolyte for maintaining your body's fluid balance as well as proper nerve and muscle function. Sodium levels are normally highest in the blood and bodily fluids that surround your cells, and are kept within a narrow concentration range by a complex balancing act of fluid intake, hormone levels and the interaction of the kidneys and adrenal glands. Hyponatremia occurs when your body loses too much sodium in disorders such as diarrhea, Addison's disease and kidney disease, or when it retains too much fluid as with congestive heart failure, liver cirrhosis and protein-losing disorders. Increased production of a chemical called anti-diuretic hormone (ADH) by your pituitary gland or some cancers can also lead to increased fluid retention and low sodium levels.
Hyponatremia and Cancer
Low sodium levels can occur in patients whose cancers produce ADH-like hormones, from other cancer complications and different treatment side effects. Cancers such as small cell lung carcinoma, pancreatic cancer, lymphoma and certain brain tumors can cause a condition known as the syndrome of inappropriate anti-diuretic hormone (SIADH) secretion. When you are in a state of SIADH, increased amounts of ADH are present even though the body's total sodium content is normal, resulting in continued water retention by the kidneys and further sodium imbalance. SIADH can also occur as a side effect of several chemotherapy drugs. Other causes of hyponatremia in cancer patients include sodium loss from vomiting and diarrhea, chemotherapy drug effects, adrenal gland insufficiency and changes in kidney or brain function.
Symptoms of Hyponatremia
As the sodium level in your blood drops, water begins to shift into your cells and cause swelling. Although not critical for most cells, swelling of the brain cells contained inside the bony skull leads to increased pressure and many of the symptoms of hyponatremia. The types of symptoms that occur depend on both how rapidly and how far your sodium levels drop. Mild hyponatremia that develops slowly may not be noticeable, or might show nonspecific symptoms such as fatigue, muscle cramps, nausea and loss of appetite. More serious hyponatremia developing over 24 to 48 hours can cause headache, confusion, seizures and coma, and represents a medical emergency.
Diagnosis and Treatment
The diagnosis of hyponatremia is made by measuring your sodium blood level and, in some cases, the urine sodium level as well as blood and urine osmolality, to help assess overall fluid balance. Immediate treatment depends on the symptoms you are experiencing and the results of the laboratory tests performed. Simple water restriction and oral electrolyte replacement can be used for mild cases of hyponatremia, but medications, intravenous electrolyte replacement and other more invasive procedures might be necessary in severe cases. For cancer-related hyponatremia, treatment and removal of the cancer should also solve a sodium imbalance.