Syndrome of Inappropriate Antidiuretic Hormone Overview
Antidiuretic hormone (ADH) is produced by an area of the
brain called the hypothalamus. The hormone is stored in and released by the
pituitary gland. ADH controls how your body releases and conserves water.
When ADH (also called vasopressin) is produced somewhere
other than the hypothalamus, the condition is called syndrome of inappropriate
antidiuretic hormone (SIADH).
In addition to making it harder for your body to release
water, SIADH can result in lowered levels of electrolytes like sodium. Early
symptoms may be mild and include cramping and nausea. In severe cases, SIADH
can cause confusion, seizures, and coma.
A variety of conditions can trigger abnormal ADH production,
but the main cause is cancer. It is frequently one of the first signs of lung
Treatment usually begins with limiting fluid intake to
prevent further buildup. Additional treatment will depend on the cause.
Another name for the syndrome is “ectopic ADH secretion.”
Symptoms of SIADH
SIADH makes it difficult for your body to get rid of excess water.
This causes a buildup of fluids as well as abnormally low sodium levels, a
condition known as hyponatremia.
Symptoms may be mild and vague at first, but tend to build. Severe
cases may involve these symptoms:
- irritability and restlessness
- loss of appetite
- nausea and vomiting
- muscle weakness
Causes of SIADH
Cancer, especially lung cancer, is the most common cause of
SIADH. SIADH is often one of the first symptoms of lung cancer.
SIADH can also be caused by tumors of the head or neck.
Other triggers for SIADH include:
- diseased or damaged hypothalamus
- encephalitis (inflammation of the brain)
- Guillain-Barré syndrome (GBS) (immune system disorder)
- heart failure
- lung disease
- meningitis (inflammation of the membranes
covering the brain and spinal cord)
- trauma to the head
Doctors will ask for a patient’s complete medical history
and current symptoms. Doctors should know whether a patient is taking over-the-counter
or prescription medications or supplements. Diagnosis usually begins with a
physical exam. Often, a urine sample is also required.
Blood tests, specifically one called an ADH test, can the measure
circulating ADH levels in the blood. According to the National Institutes of
Health (NIH), normal values for ADH range from 1-5 picograms per milliliter (NIH,
2011). Higher levels could be the result of SIADH.
Following diagnosis of SIADH, the next step will be to
identify the condition that caused it to occur.
Treatment for SIADH
The first line of treatment is to limit fluid intake to
avoid further buildup. Medications may include those that can reduce fluid
retention, such as furosemide (Lasix), and those that can inhibit ADH, like demeclocycline.
Any underlying medical conditions must be treated. If a
patient is diagnosed with cancer, treatment may include surgical removal of a
tumor or tumors, chemotherapy, and radiation.
A patient’s prognosis
will depend on the cause of SIADH.