What is SIADH?

To function properly, every cell in our bodies needs to a certain level of salt. When the salt balance in the body is disturbed, many things can start going wrong.

Antidiuretic hormone (ADH), also known as vasopressin, controls the way your body retains or secretes water. ADH causes the body to retain water, which lowers the salt concentration throughout the body. The syndrome of inappropriate secretion of antidiuretic hormone, SIADH for short, occurs when your body makes too much ADH. 

SIADH is the most common cause of low body salt (known as hyponatraemia). [1]

SIADH is caused by too much antidiuretic hormone in the body, which reduces salt concentration in the blood. 

Antidiuretic

A substance that suppresses the production and excretion of urine.

Hormone

A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.

1. Ellison, D.H. & Berl, T. (2007). The Syndrome of Inappropriate Antidiuresis. New England Journal of Medicine 356: 2064–2072.

Causes

SIADH can be the result of numerous different disorders, including, but not limited to:

Brain and nerve disorders:

Cancer:

Lung disorders

Medications:

SIADH can be a side effect of certain medications and substances, such as:

Other causes:

  • After-effects of surgery;
  • Genetic disorders, such as porphyria, and;
  • Unknown causes.

Abscess

A swollen area of tissue containing a build-up of pus.

Antidepressants

Medication used to treat depression and other mood disorders.

Antipsychotic

Medications used to treat symptoms of psychosis, such as hallucinations, delusions and/or thought disorders.

Carcinoma

Cancer of the tissues lining the internal organs, body cavities, surfaces and tubes.

Delirium tremens

An acute condition caused by alcohol withdrawal that causes tremors, anxiety, sweating and hallucinations. Colloquially called 'the D.Ts'.

Encephalitis

Inflammation of the brain, usually caused by a viral infection.

Endometrial

Relating to the internal lining of the uterus.

Genetic

Related to genes, the body's units of inheritance or origin.

Hormone

A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.

Hypothalamus

A small part of the brain that carries out many functions, in particular the communication between the nervous system and the endocrine system (via the pituitary gland).

Lymphoma

A tumour of lymph tissue, which is rich in lymphocytes, small white blood cells that have specific immune responses.

Pituitary gland

A small gland located at the base of the brain which produces many hormones important for the healthy function of the body.

Psychosis

An abnormal mental state characterised by a loss of contact with reality.

Sarcoma

A cancer that arises from connective tissues such as fat, bones, muscles and blood vessels.

Shy-Drager syndrome

A rare genetic disease that causes progressive death of nerve cells in the brain and spinal cord.

Guillain-Barre syndrome

An autoimmune condition triggered by an acute infection, which leads to inflammation of peripheral nerves causing a characteristic pattern of paralysis that begins at the feet and spreads up the body.

Nasopharyngeal cancer

Cancers arising in the lining of the nose, sinuses and throat.

Porphyria

A group of conditions caused by defective enzymes, which leads to a build-up of metallic compounds (known as porphyrins) normally found in tissues. The abnormal accumulation of porphyrins affects the skin, digestive system and/or nervous system, leading to symptoms such as skin blisters, abdominal pain or seizures.

1. Ellison, D.H. & Berl, T. (2007). The Syndrome of Inappropriate Antidiuresis. New England Journal of Medicine 356: 2064–2072.

Signs and symptoms

Symptoms of SIADH can appear and become more severe as the body's salt concentration drops. These symptoms may include [2] [3] :

Many people with mild SIADH often have no symptoms, or their symptoms may not be recognised as SIADH symptoms. This is especially common in elderly people, where reduced mental abilities - for example, poor concentration or forgetfulness - are often blamed on age or other causes [4] .

Coma

A state of deep and prolonged unconsciousness.

Incontinence

The uncontrollable loss, small or large, of bladder or bowel control, resulting in leakage of their contents.

Nausea

A sensation of sickness and unease, typically felt in the stomach, often accompanied by the urge to vomit. Nausea is a common symptom with many possible causes.

Seizures

A sudden, involuntary contraction of muscle groups caused by abnormal electrical activity in the brain.

Stomach

The first major site of digestion. An organ in the abdomen where food incoming from the food pipe is digested with enzymes and acidic gastric juices.

Hallucinations

A false perception of something that is not actually there. The perception can be visual or aural.

2. Hannon, M.J. & Thompson, C.J. (2010). The syndrome of inappropriate antidiuretic hormone: prevalence, causes and consequences. European Journal of Endocrinology 162: S5–S12.

3. Hoorn, E.J., Lubbe, N. van der & Zietse, R. (2009). SIADH and hyponatraemia: why does it matter? NDT Plus 2: iii5–iii11.

4. Gross, P. (2012). Clinical management of SIADH. Therapeutic Advances in Endocrinology and Metabolism 3: 61–73.

Methods for diagnosis

Your doctor will suspect SIADH if you display symptoms and have a medical condition or history that would put you at risk of SIADH. To confirm the diagnosis and rule out other conditions, urine tests and blood tests will be done to check your salt levels.

Blood tests

During a blood test, blood can be drawn using a needle or by a finger prick. Your blood can then be analysed to help diagnose and monitor a wide range of health conditions.

Urine tests

A routine examination of the urine for cells, microbes, or chemicals that can indicate a range of different illnesses.

2. Hannon, M.J. & Thompson, C.J. (2010). The syndrome of inappropriate antidiuretic hormone: prevalence, causes and consequences. European Journal of Endocrinology 162: S5–S12.

3. Hoorn, E.J., Lubbe, N. van der & Zietse, R. (2009). SIADH and hyponatraemia: why does it matter? NDT Plus 2: iii5–iii11.

4. Gross, P. (2012). Clinical management of SIADH. Therapeutic Advances in Endocrinology and Metabolism 3: 61–73.

Types of treatment

Treatment of SIADH can take several forms:

  • A high-salt infusion can be used to treat acute cases of SIADH in the short term;
  • SIADH can be cured if the underlying medical condition or cause is treated. For instance, if SIADH is the side effect of a particular medication, adjusting the dose or using an alternative medication often helps reverse SIADH;
  • If the underlying cause is not treatable, it is often best to treat SIADH with fluid restriction, which is limiting the amount of water a person drinks. Your doctor will advise you how to safely do this;
  • Treatment with diuretic medication, such as frusemide, can encourage the body to get rid of excess water, and;
  • Medications called 'vaptans', or vasopressin-receptor antagonists, have recently begun to be used to treat SIADH. Vaptans limit ADH activity; however, these medications are not widely available. [1]

1. Ellison, D.H. & Berl, T. (2007). The Syndrome of Inappropriate Antidiuresis. New England Journal of Medicine 356: 2064–2072.

Potential complications

If not treated, SIADH can lead to very low salt concentrations, which can interfere with the function of many of the body's systems, and is associated with a significant rise in illness and death rates [2] .

2. Hannon, M.J. & Thompson, C.J. (2010). The syndrome of inappropriate antidiuretic hormone: prevalence, causes and consequences. European Journal of Endocrinology 162: S5–S12.