Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

Author: OncoLink Team
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What is Syndrome of Inappropriate Antidiuretic Hormone (SIADH)?

The hypothalamus is a part of the brain that, among other things, makes hormones. Antidiuretic hormone (ADH) is normally made by the hypothalamus. When ADH is made somewhere in the body other than the hypothalamus, it is called syndrome of inappropriate antidiuretic hormone (SIADH). ADH is made “inappropriately” in the body.

The job of antidiuretic hormone, also known as vasopressin, is to retain (hold onto) water in the body. Antidiuretic hormone is made in the hypothalamus and is stored and released by the pituitary gland. When the body is dehydrated, ADH is released, causing the body to conserve (hold on to) water, resulting in urine becoming more concentrated and reducing the amount of urine being made.

In SIADH, the body retains, or holds onto, too much fluid (water). This dilutes the sodium level in the body. That is, as fluid builds up in the body, it makes your body think there is not enough sodium. Your body responds as if sodium levels are low, called hyponatremia. However, in reality, there is enough sodium in the body.

Cancer, including lung and head and neck cancers, is the most common cause of SIADH. Other causes include: meningitis, psychosis, lung disease, head trauma, some medications, and damage to the hypothalamus or pituitary gland.

Symptoms of SIADH are similar to that of hyponatremia (low sodium levels). Symptoms tend to be mild at first and include cramps, muscle weakness, loss of appetite, irritability, and nausea and vomiting. The symptoms continue to become more serious if the SIADH goes untreated and include confusion, hallucinations, seizures and even coma.

Diagnosing SIADH requires a medical history and a review of symptoms and medications by your provider. Urine and blood tests may be used to diagnose SIADH.

How is SIADH treated?

SIADH is treated in a variety of ways:

  • Treatment of underlying condition – If your SIADH is being caused by cancer, your cancer may be treated with surgery, chemotherapy, or radiation if appropriate. Any other underlying conditions should also be treated.
  • Fluid Restriction – Your provider may limit the amount of fluid you take into your body through food and drinks. This will help prevent further fluid retention. Your provider will monitor you to prevent dehydration.
  • Medication – You may be prescribed a loop diuretic such as furosemide (Lasix). Lasix is a diuretic, which decreases fluid in your body by increasing the amount of urine you produce. The more urine you produce, the less extra fluid is in your body. Because your body will be producing more urine, your provider will closely monitor your electrolytes. Some electrolytes leave the body through the urine and this increase in urine output can lower the levels of some electrolytes.

When to contact your care team

If you are gaining too much fluid weight, or notice new or worsening swelling, call your provider right away. Your care team may ask you to weigh yourself at least once a day and will give you instructions for when to call your provider. If you have symptoms such as weakness, confusion, cramps, irritability, or nausea and vomiting contact your care team for immediate evaluation.

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