Syndrome 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.
Definition & Facts
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
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:
- Swelling around the brain causing headaches, seizures, confusion, and irritability
- Muscle cramps
- Decreased reflexes
- Weight gain
- High blood pressure (hypertension)
SIADH is very serious often requiring hospitalization. If severe hyponatremia is left untreated, brain damage or death can occur.
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:
- Thyroid levels (Thyroid stimulating hormone (TSH))
- Cortisol levels
- Basic metabolic panel (BMP) which includes blood urea nitrogen (BUN) and creatinine which indicate kidney function and electrolytes (sodium, potassium, calcium, magnesium)
- Liver function tests (LFT)
- Blood cell counts
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.
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
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.