SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion)

What is SIADH (syndrome of inappropriate antidiuretic hormone secretion)?

SIADH (syndrome of inappropriate antidiuretic hormone secretion) is a condition in which your body makes too much antidiuretic hormone (ADH).

ADH, also known as vasopressin, is a hormone that your hypothalamus makes and your posterior pituitary stores and releases.

ADH plays a role in the following processes:

• The balance of water and salt (sodium) in your blood.
• Blood pressure regulation.
• Kidney functioning.

More specifically, ADH helps your kidneys control the amount of water your body loses through your pee. SIADH causes your body to retain too much water.

The main sign and consequence of ADH is hyponatremia, which is when you have low levels of sodium (salt) in your blood.

Who does SIADH affect?

SIADH can affect anyone, but the likelihood of the condition increases with age.

SIADH is more common in people who are recovering from surgery in a hospital due to the administration of fluids, certain medications and their body's response to pain and stress. It’s also commonly found in people with lung cancer, in particular, small-cell lung cancer (SCLC).

How common is SIADH?

SIADH is somewhat common. Hyponatremia, the main medical consequence of SIADH, is the most common electrolyte imbalance found in people in the hospital, and SIADH is the most common cause of the condition.

How does SIADH lead to hyponatremia?

Antidiuretic hormone (ADH) mainly affects your kidneys’ ability to reabsorb water. Under normal circumstances, your body signals ADH release for a variety of reasons.

For example, if you’re dehydrated, your body will signal the release of ADH so that your kidneys release less water through your pee in order to “save” or reuse more water for your body. If you treat the dehydration by drinking water, your body stops signaling ADH release, and your kidneys release more water through your pee.

In most people with SIADH, drinking water doesn’t adequately suppress ADH release, and their pee remains concentrated. This leads to water retention, which dilutes your blood. This then leads to low levels of sodium in your blood (hyponatremia).

In some cases of SIADH, the increase in water in your body signals your kidneys to release an increased amount of salt in your pee. This also contributes to hyponatremia.

What are the symptoms of SIADH?

With SIADH, your pee is very concentrated, meaning there’s a lot of waste product and not much water in it. Since your body doesn’t release normal amounts of water through your pee, there’s too much water in your blood. This dilutes many substances in your blood, such as sodium (salt).

A low blood sodium level (hyponatremia) is the most common cause of symptoms of SIADH.

Often, mildly low sodium levels don’t cause symptoms, but moderate to severe hyponatremia can cause the following symptoms:

• Muscle cramps or weakness.
• Nausea and vomiting.
• Headache.
• Problems with balance, which may result in falls.
• Mental changes, such as confusion, memory problems and/or strange behavior.
• Seizures or coma (in severe cases).

What causes SIADH?

Most commonly, SIADH happens due to another medical condition. Hereditary SIADH (nephrogenic SIADH) is rare. This is due to a mutation (gene change) in vasopressin 2 (V2) receptors in your kidneys.

Conditions and situations that frequently lead to SIADH include:

• Certain cancers: Certain tumors can produce their own ADH, leading to excess ADH in your body and SIADH. Small cell lung cancer (SCLC) is the most common tumor leading to excess ADH production. Less commonly, other cancers can lead to SIADH, including extra-pulmonary small cell carcinomas, head and neck cancers and olfactory neuroblastomas.
• Central nervous system (CNS) issues: Your CNS includes your brain and spinal cord. Any abnormality in this system can lead to SIADH, including stroke, hemorrhage (bleeding), infection, trauma (injury) and psychosis (rare).
• Certain medications: Several medications can cause SIADH by enhancing the release or effect of ADH. They include certain seizure drugs; antidepressants; cancer drugs; and heart, diabetes and blood pressure drugs.
• Surgery under general anesthesia: Surgical procedures are often associated with SIADH, likely due to stress on your body.
• Lung disease: Lung diseases, particularly pneumonia (viral, bacterial, tuberculosis), can lead to SIADH. Researchers aren’t sure why this happens.
• Hormone deficiency: Both hypopituitarism and hypothyroidism may lead to SIADH.

How is SIADH diagnosed?

If you’re having symptoms of hyponatremia, your healthcare provider will perform a complete physical examination. They’ll also establish your fluid status, which is an important part of making the correct diagnosis. They’ll look at whether you have dehydration, too much water in your body or the appropriate amount.

There’s no single best test to diagnose SIADH. While there are tests to measure ADH levels in your blood, it can take up to two weeks to get the results.

Because of this, your provider will likely order other tests to check for hyponatremia, including:

• Comprehensive metabolic panel (CMP).
• Osmolality blood test.
• Urine osmolality test.
• Urine sodium and potassium test.
• Toxicology screens for certain medications.

If your child has symptoms of SIADH, their provider may order lung and brain imaging tests.

How is SIADH treated?

Treatment for SIADH depends on its cause. For example, if you have a tumor that’s producing ADH, your healthcare provider may recommend surgery to remove it. If a medication is the cause, your provider may change the dosage or have you try a different drug.

In all cases of SIADH, the first step is to limit your fluid intake. This helps prevent excess fluid from building up in your body. Your provider will tell you what your total daily fluid intake should be, including water, coffee, tea, soda, etc.

If you have severe symptoms of hyponatremia, such as confusion and seizures, it’s a medical emergency. Providers typically treat this with a salt solution you get through an IV in the hospital.

You may need medications to block the effects of ADH on your kidneys so that they can signal your body to release excess water through your pee.

Can SIADH be prevented?

Since there are so many possible causes of SIADH, it’s usually not possible to prevent it. If you’re concerned about your risk of developing SIADH or hyponatremia, talk to your healthcare provider.

What is the prognosis of SIADH?

The prognosis (outlook) of SIADH depends on the underlying cause of it. The good news is that many causes of SIADH are reversible and/or treatable.

Low sodium that occurs rapidly, in less than 48 hours (acute hyponatremia), is more dangerous than low sodium that develops slowly over time.

Chronic hyponatremia is associated with nervous system issues, such as poor balance and poor memory.

In severe cases of SIADH, very low sodium levels can lead to:

• Decreased consciousness, hallucinations or coma.
• Brain herniation.
• Death.

When should I see my healthcare provider about SIADH?

If you’re experiencing symptoms of hyponatremia, such as muscle cramps or issues with balance, talk to your healthcare provider. There are several possible causes of these symptoms, so your provider may order multiple tests to rule out conditions.

If you’re experiencing symptoms of severe hyponatremia, such as confusion, delirium or seizures, get to the nearest hospital as soon as possible.

A note from Cleveland Clinic

SIADH (syndrome of inappropriate antidiuretic hormone secretion) is a somewhat common condition that has several possible causes. It mostly affects people who are already in the hospital. However, if you’re experiencing symptoms of SIADH, such as muscle cramps or mental changes, it’s important to talk to your healthcare provider.