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SIADH stands for syndrome of inappropriate antidiuretic hormone hypersecretion. It is characterized by very high antidiuretic hormone (ADH) levels in the body, which can lead to water retention and low blood sodium levels. SIADH can be caused by many factors, including several types of cancer, drugs such as chlorpropamide, infections, and brain lesions. When ADH levels are too high, a person can experience mental confusion, extreme physical fatigue, and possibly life-threatening lung, brain, and heart complications. The condition is usually treated with drugs that block ADH activity and the appropriate therapies for the underlying cause.
ADH that is secreted by the pituitary gland contributes to proper kidney functioning. It helps regulate the levels of water, sodium, potassium, and other important minerals in the bloodstream and urine. When there is too much of the hormone due to SIADH, the body retains water and large amounts of sodium are expelled in urine. The resulting low sodium levels can wreak havoc on many of the body's systems and organs.
SIADH is frequently caused by cancerous tumors, especially small cell lung carcinomas. Tumors may begin producing and releasing their own ADH or signal the pituitary to increase secretion. Certain medications for depression, diabetes, blood pressure, and other conditions may also trigger ADH release. Lung disease and central nervous system infections have also been linked to the development of SIADH.
Symptoms of SIADH become prevalent once sodium levels become very low. Fatigue, headache, restlessness, and nausea are common. A person may also experience painful muscle cramps and spasms, mental confusion, and mild hallucinations. Left untreated, the condition can cause seizures and loss of consciousness. The kidneys, liver, lungs, and heart can shut down if emergency care is not available.
Doctors diagnose SIADH by examining sodium levels in blood and urine samples. If the underlying cause is not already known, imaging scans, kidney biopsies, and additional blood work may be necessary to look for tumors and infections. Patients who are in critical condition may need oxygen therapy, dialysis, and intravenous fluids while diagnostic tests take place. ADH receptor agonists, drugs that block ADH functioning, are usually given at the hospital to return sodium levels to normal.
Once the cause is discovered, long-term treatment plans can be made. Cancer patients may need to undergo surgery, radiation, or chemotherapy, and people with severe infections might need antibiotics and other drugs. A patient might need to continue taking ADH receptor agonists and restrict his or her fluid intake throughout treatment. When the cause is found early and treated appropriately, most people are able to recover from SIADH.