Syndrome of inappropriate antidiuretic hormone

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at October 18, 2016
StartDiseasesSyndrome of inappropriate antidiuretic hormone

Syndrome of inappropriate antidiuretic hormone, also referred to as SIADH, is a condition caused by various illnesses or injuries to the human body. SIADH causes an imbalance in sodium and fluid levels and can be very dangerous if left untreated. This condition may require hospitalization.

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Definition & Facts

Syndrome of inappropriate antidiuretic hormone (SIADH) is a condition that causes the body to retain water and significantly decrease the amount of sodium that circulates in the bloodstream.

SIADH happens when too much antidiuretic hormone (ADH) is produced by the pituitary gland. Under normal circumstances, ADH is secreted by the pituitary gland to help regulate water balance in the body. When too much ADH is produced, the body holds onto water instead of excreting it, causing necessary blood sodium levels to decrease which is called hyponatremia.

Many conditions and illnesses such as cancer, tumors, injuries to the head, brain surgery, and respiratory conditions can cause SIADH. This is a fairly common condition with over 200,000 people affected each year in the US. While SIADH can occur at any age, the majority of cases are found in people 60 years and older.

Symptoms & Complaints

Signs and symptoms of syndrome of inappropriate antidiuretic hormone can vary depending on how severely out of balance the hormone secretion, water balance and sodium levels are.

An individual whose water balance and sodium levels have decreased slowly over time may not have any symptoms or will likely experience vague symptoms such as headache, fatigue, irritability, extreme thirst, and loss of appetite. People who experience a very quick and severe decrease in their sodium levels, usually over 48 hours, will display more serious symptoms such as:

SIADH is very serious often requiring hospitalization. If severe hyponatremia is left untreated, brain damage or death can occur.

Causes

The causes of SIADH are varied in nature and are many, however they can be generally linked to three main categories. The first is malignant disease, or certain cancers. Cancer cells can cause many disruptions in the normal functionality of the human body. Fluid and electrolyte (sodium, potassium, magnesium, etc.) imbalance often result from malignant tumors.

Whenever the body's functioning is disrupted, certain hormones may be released to help correct the problem. A particular lung cancer, bronchogenic carcinoma, has been found to be directly related to causing SIADH because the abnormal cells associated with this cancer cause a release of too much ADH (antidiuretic hormone). 

The second category is respiratory disease or illness. People with pneumonia, respiratory failure, or those with a condition called atelectasis which is common after surgery or when someone is immobile for a long time, are prone to developing SIADH.

Finally, conditions of the central nervous system can cause SIADH. The pituitary gland is responsible for regulating how much ADH is released into the body. This gland is located at the base of the brain. Therefore tumors, infections such as meningitis, brain surgery or injuries to the head can all cause imbalances that may lead to SIADH. 

Diagnosis & Tests

Syndrome of inappropriate antidiuretic hormone is diagnosed with a series of imaging and laboratory tests. Studies such as X-ray and computed tomography (CT) scan can help scan for signs of cancer such as tumors or abnormal growths or help practitioners see an abundance of fluid in the body indicating water retention. Laboratory testing by drawing a blood sample may include:

A doctor will likely want to take a urine sample in order to determine the level of sodium that is being excreted from the body. A high urine sodium and low blood sodium level indicates SIADH.

Treatment & Therapy

The only guaranteed cure for SIADH is to eliminate the cause. Treatment of cancer, infection or injury leading to SIADH is necessary. Usually, simultaneously the symptoms of SIADH will be treated. For those individuals who have experienced low sodium levels over time, their bodies have gotten used to this state and rapid correction of the sodium and fluid balance can be dangerous. Therefore, restricting the amount of fluid the individual can drink is often a first step.

Infusing a high concentration of a sodium solution through an IV very slowly may also be a course of treatment. A medication called demeclocycline has been found to help regulate sodium levels. 

For people with severe SIADH, the standard of treatment is IV infusion of highly concentrated saline (sodium fluid). The goal is to correct the condition fairly quickly, but in a very controlled manner. Diuretics are often administered along with the IV saline to help the body excrete extra water.

Recent studies support the use of vasopressin receptor antagonist therapy. These are medications that block the antidiuretic hormone in the kidneys allowing for increased urination to decrease the retained fluid in the body. 

Prevention & Prophylaxis

Living a healthy lifestyle including a nutritious diet and regular exercise can help to avoid many of the conditions that can be precursors to SIADH. However, injuries, infections and cancer can't be predicted or always prevented. Understanding the causes and the signs and symptoms of SIADH can help to prevent the occurrence of the condition.

If an individual is diagnosed with one of the causes of SIADH, the treating physician may order regular testing and lab work to monitor sodium levels in the blood and urine and also fluid balance within the body. The most important method of prevention is to be in tune with what is normal for each person. If any of the signs or symptoms are experienced, it is important to speak with a doctor right away.