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Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is when you have too much antidiuretic hormone (ADH) circulating in your body. Antidiuretic hormone (ADH), also called arginine vasopressin (AVP), is produced in your hypothalamus at the base of your brain and stored in your pituitary gland. ADH helps regulate the balance of fluids in your body.
Read on to learn about syndrome of inappropriate antidiuretic hormone secretion (SIADH) symptoms, causes, and treatments. This article will also discuss the risk factors and diagnosis of SIADH and answer frequently asked questions.
ADH is necessary to maintain the volume of blood in your body. It does this by regulating the amount of water your kidneys retain and the amount of urine they produce. Learn about ADH here.
With SIADH, your pituitary gland is secreting ADH when it should not. If ADH is too high, your body retains water (hypervolemia), the electrolytes in your body become unbalanced, and the amount of sodium in your blood falls (hyponatremia). However, a person with SIADH may have usual fluids and still have low sodium. This is euvolemic hyponatremia.
Medical management of SIADH depends on the severity. The goal is to restore the body’s balance of water and salt. Treatments can include water restriction, IV administration of a concentrated sodium solution, and medications that block ADH.
Without treatment, hyponatremia can damage the central nervous system (CNS) and lead to coma. SIADH is a medical emergency when it develops suddenly, and sodium levels fall abruptly.
SIADH usually develops as a consequence of some other condition. Disturbances in your CNS and certain tumors, infections, and medications can cause SIADH.
William Schwartz, founder of the Division of Nephrology in 1950 at what is now Tufts Medical Center in Boston, and endocrinologist Frederic Bartter introduced the term syndrome of inappropriate antidiuretic hormone in 1957 when describing two patients affected by lung tumors.
A lack of ADH leads to diabetes insipidus, which is when your kidneys remove too much fluid. People with diabetes insipidus produce a large amount of urine, and dehydration is possible. Doctors treat diabetes insipidus with artificial vasopressin.
In the beginning stages of SIAHD, when sodium levels start to fall, symptoms may be mild. They can include:
In the later stages, sodium levels drop, and fluid retention makes the brain swell. Symptoms can include:
Your body can produce too much ADH for many reasons. These include:
CNS conditions that can lead to SIADH include:
SIADH is relatively common with:
Infectious diseases that may cause SIADH include:
Many medications can lead to SIADH including:
Other potential causes include:
An inherited mutation in the V2R gene is a possible cause of hyponatremia. Instead of affecting ADH secretion, the mutation affects how your body processes ADH. This means you can develop symptoms of SIADH even when ADH levels are standard.
Risk factors for SIADH include:
The criteria for diagnosing SIADH have not changed since the first description of the condition in 1957.
If you develop the symptoms listed above, your doctor will try to identify a possible cause. They will begin by taking your medical history. They will ask about any head injury, unexplained weight loss, breathing difficulties, drug intake, and substance misuse. They will also do a physical exam.
If you have regular blood and urine tests while undergoing treatment for another condition, your care team may see your sodium levels decrease before you develop symptoms. This is hyponatremia. They will begin treatment right away while also determining whether the underlying cause is SIADH.
There is no single best test to diagnose SIADH. Doctors use the following SIADH laboratory tests to help reach a diagnosis:
Your doctor will cancel out other possible causes for your fluid retention. These include:
If there is no other explanation for fluid retention and hyponatremia, your doctor may diagnose SIADH.
For mildly low sodium due to SIADH, your doctor may restrict your intake of fluids. This will gradually increase your sodium levels.
If you have SIADH neurological symptoms, your doctor will give you 3% saline IV infusions at intervals to raise your sodium levels and help prevent damage to your nervous system.
Recent studies suggest that the medication, tolvaptan (Samsca), is an effective treatment for SIADH. It helps raise sodium levels by blocking ADH. However, further studies are necessary to determine whether tolvaptan should be the first-line treatment for SIADH.
Other treatments depend on the underlying cause of SIADH. For example, you may need surgery to remove a tumor causing SIADH.
Depending on the severity of your condition, you may receive treatment in a hospital setting.
The outlook for SIADH depends on its underlying cause and the effects of water retention. For example, if medications are the underlying cause of SIADH, symptoms usually go away when you stop taking the medications.
If your treatment includes IV saline, your doctor will monitor you carefully to ensure blood sodium levels rise slowly. Overcorrection, when sodium levels rise too quickly, can damage the CNS. When correction occurs too quickly, administration of desmopressin (DDAVP), which acts like vasopressin, can safely slow the correction. This improves the outlook.
People with cancer who develop SIADH tend to have a less favorable outlook.
Megan Soliman, M.D., has reviewed the following frequently asked questions.
The most common cause of SIADH is difficult to identify with accuracy. Cancer, certain medications, and various CNS conditions are common causes of SIADH.
Severe complications include:
Many cancers can cause SIADH. Small cell lung cancer, extrapulmonary small cell carcinomas, head and neck cancers, and olfactory cancers also cause SIADH.
SIADH is a metabolic condition in which the pituitary gland secretes ADH when it should not. It develops as a consequence of another condition. SIADH increases the concentration of ADH in your bloodstream. This makes your body retain water and can lower sodium to dangerously low levels. Treatment of SIADH aims to resolve the underlying cause of the condition and correct sodium levels.
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