What is the Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)?

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is caused by the inability to suppress the secretion of antidiuretic hormone (ADH) (“inappropriate” secretion) leading to impaired water excretion.


Why is SIADH an emergency?

While the body has an excellent system to increase thirst when needed, the opposite: decrease of thirst when not needed is not well regulated. Therefore, in SIADH, the increased antidiuretic hormone secretion leads to abnormal concentration of urine and retention of water which will eventually dilute sodium in blood.

In order for the body to restore its balance, it moves water into the cells, resulting in their swelling. Depending on the speed and severity of this change, nerve cells, which are particularly sensitive to any change, may not be able to adapt resulting in serious complications, especially in young women and children, such as:

  • cerebral oedema
  • coma
  • death

What are the causes of the syndrome?

The causes of the syndrome are:

  • ectopic production of antidiuretic hormone by tumors, such as small cell lung cancer
  • certain medications, such as antidepressants and antiepileptics
  • a wide range of disorders and lesions, both in the brain, (infection, trauma, bleeding, surgery), and in the lungs, (pneumonia, tuberculosis)
  • acquired immune deficiency syndrome (AIDS)
  • prolonged strenuous exercise (e.g marathon running)
  • but also, a rare genetic mutation.

What are the symptoms, signs and complications of the syndrome?

The clinical picture of the syndrome ranges from very mild neurological symptoms not easily noticeable, but they increase the likelihood of falls and fractures, such as:

  • lack of balance and trouble walking
  • drowsiness

To more severe neurological symptoms such as:

  • nausea,
  • vomiting,
  • cerebral oedema,
  • coma and
  • death

How is the diagnosis of the syndrome made?

Diagnosis of the disease is made by exclusion. A number of diseases should be excluded, as well as the case of pseudo-hyponatreamia.


What is the treatment of the syndrome?

Treatment of the syndrome depends on the degree of hyponatremia, the symptoms and whether the drop of sodium is acute or chronic and includes:

  • restriction of fluid intake,
  • administration of antidiuretic hormone receptor inhibitors and
  • urgent treatment of acute conditions, usually accompanying acute hyponatremia, and can threaten life.