Syndrome of inappropriate antidiuretic hormone (SIADH) is when the brain’s hypothalamus makes too much antidiuretic hormone (ADH), which controls how your body releases and conserves water.

SIADH makes it harder for your kidneys to release water and causes the levels of electrolytes, like sodium, to fall due to water retention.

Read on to learn more about SIADH, what it is, its symptoms, diagnosis, and treatment.

The brain’s hypothalamus produces ADH, which is stored in and released by the pituitary gland. ADH helps the body correct for abnormal fluid loss, retain water, and preserve healthy blood pressure.

Problems occur when the pituitary releases too much ADH. Moreover, the overproduction of ADH can occur in places other than the pituitary gland.

SIADH was first discovered in 1967 in two people with lung cancer. It usually occurs due to an underlying medical condition like cancer or others.

A low sodium level or hyponatremia is a major complication of SIADH and is responsible for many of its symptoms. Early symptoms may be mild and include cramping, nausea, and vomiting. In severe cases, SIADH can cause confusion, seizures, and coma.

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.”

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.

Symptoms may be mild and vague at first but tend to build. Severe cases may involve these symptoms:

  • irritability
  • loss of appetite
  • nausea and vomiting
  • muscle cramps
  • confusion and disorientation
  • headache
  • difficulty with attention

More severe symptoms may include:

  • hallucinations
  • respiratory failure
  • seizures
  • coma

Without treatment, SIADH can lead to death.

A variety of conditions can trigger abnormal ADH production, including:

In some cases, SIADH may also be genetic.

The treatment for SIADH can depend on your symptoms’ severity and the underlying cause. But, the first line of treatment is usually the limitation of fluid intake to avoid further buildup and oral or IV administration of a sodium solution. These steps help restore fluid and electrolyte balance in the body.

Medications may include those that can reduce fluid retention, such as furosemide (Lasix), and those that can inhibit ADH, like demeclocycline (Declomycin). Another medication called Tolvaptan (Samsca) may also be used.

Your doctor will usually begin by asking for your complete medical history and current symptoms. They should know whether you take any over-the-counter or prescription medications or supplements. They will then do a physical exam.

There is no exact way to test for SIADH. Your doctor may first identify symptoms of hyponatremia and will then want to measure the levels of sodium and the balance of water and electrolytes in your urine and blood.

If these are too low, they will want to rule out other causes before diagnosing you with SIADH. Following a diagnosis of SIADH, the next step will be to identify the condition that caused it to occur.

SIADH causes the brain to make too much ADH. This leads to problems with releasing water and an electrolyte imbalance, particularly low sodium.

SIADH can be treated by restoring sodium balance and helping the body stop retaining water. But a doctor will also need to identify and treat the underlying cause.

SIADH can present as mild but, in some cases, can be severe and life threatening. Your prognosis will depend on the cause of SIADH and what additional treatment may be necessary.